Content uploaded by Mahendra Pal
Author content
All content in this area was uploaded by Mahendra Pal on May 22, 2016
Content may be subject to copyright.
Journal of Foodborne and Zoonotic Diseases | January-March, 2016 | Vol 4 | Issue 1 | Pages 01-14
© 2016 Jakraya Publications (P) Ltd
JOURNAL OF FOODBORNE AND ZOONOTIC DISEASES
Journal homepage: www.jakraya.com/journal/jfzd
ORIGINAL ARTICLE
Studies on the Prevalence, Risk Factors, Public Health Implications and
Antibiogram of Listeria monocytogenes in Sheep Meat Collected from Municipal
Abattoir and Butcher Shops in Addis Ababa
S. Mulu and M. Pal*
*Department of Microbiology, Immunology and Public Health, College of Veterinary Medicine and Agriculture,
Addis Ababa University, P.B.Box No 34,Debre Zeit, Ethiopia.
*Corresponding Author:
Prof. Mahendra Pal
Email: palmahendra2@gmail.com
Received: 12/03/2016
Revised: 27/03/2016
Accepted: 29/03/2016
Abstract
Listeria monocytogenes, the chief cause of listeriosis, is one of the
important emerging food-borne bacterial zoonotic pathogens of global
significance. The present study was undertaken to determine the presence
of L. monocytogenes in raw meat of market and abattoir. A cross-sectional
study was conducted from October 2013 to April 2014 to isolate L.
monocytogenes from swab samples on sheep meat from abattoir, butcher
shops, equipments, and also to determine antibiotic resistance profiles of
the isolates. A total of 873 swab samples comprising of 384 from the
abattoir and 384 from butcher shops were obtained aseptically using
systematic random sampling technique, and 105 swabs were collected from
equipments. Questionnaire survey was conducted to assess the hygienic
practices of meat production in raw meat of market and abattoir, and
possible risk factors regarding the contamination of sheep meat. Listeria
monocytogenes was isolated and identified using standard bacteriological
techniques. Antimicrobial susceptibility test was also conducted on 36
isolates of L. monocytogenes. The overall prevalence of L. monocytogenes
was 4.1%; and the prevalence of 2.1%, 5.5%, and 6.7% was recorded from
abattoir, butcher shops, and equipments, respectively. The study also
revealed multi-drug resistant isolates in 24/36 (66.7%) of two or more
antimicrobials. In addition, the presence of L. monocytogenes attributed to
unclean working environment and improper handling of meat, till it reaches
to the consumer. Preventive measures to avoid the presence of pathogenic
L. monocytogenes in raw meat and meat products should be undertaken,
emphasizing the need for improved hygienic practices during meat
production, and also during distribution, and consumption of the final
products.
Keywords: Abattoir, Addis Ababa, Antimicrobial susceptibility, Hygienic
practice, Listeria monocytogenes, Prevalence, Sheep meat.
1. Introduction
Animals are important as producers of meat,
milk, and eggs, which are part of the food chain and
provide high value of protein food. They have long
played a key role in supplying calories, and protein for
human food in virtually all parts of the world, both
directly in the form of animal products, and indirectly
from the contribution of manure and draught power to
crop production and generation of income to enable
purchase of food (ESAP, 2001). Animals naturally
harbor many food-borne bacteria in their intestines that
can cause illness in humans, but often do not cause
illness in the animals. During slaughter, meat and
poultry carcasses can become contaminated, if they are
exposed to small amounts of intestinal contents (Pal,
2015; Pal and Mahendra, 2015).
Food safety has emerged as an important global
issue with international trade and public health
implications. Listeria monocytogenes associated with
outbreaks have been reported from a wide variety of
foods (Pal, 2013; Pal and Awel, 2014). The bacterium
has been isolated from meat, poultry, milk, cheese, and
other dairy products, and vegetables (Antunes et al.,
2002; Kumar, 2011; Khan et al., 2013; Pal and Awel,
2014; Pal, 2015). L. monocytogenes is a significant
pathogen of food safety concern, as it can induce
Mulu and Pal…Studies on the Prevalence, Risk Factors, Public Health Implications and Antibiogram of Listeria
monocytogenes in Sheep Meat Collected from Municipal Abattoir and Butcher Shops in Addis Ababa
Journal of Foodborne and Zoonotic Diseases | January-March, 2016 | Vol 4 | Issue 1 | Pages 01-14
© 2016 Jakraya Publications (P) Ltd 2
disease in humans, and can be transferred to food
products derived from animals (Hassan et al., 2000;
Pal, 2013).
Food-borne pathogens are the leading cause of
illness and death in many countries of the world
costing billions of dollars in medical care and medical
and social costs (Pal and Mahendra, 2015). Changes in
eating habits, mass catering, complex and lengthy food
supply procedures with increased international
movement, and poor hygiene practices are major
contributing factors (Nafisa et al., 2010; Pal and
Mahendra, 2015). The modern food industry aims to
decrease the use of preservatives, and to increase shelf
lives, so the food safety is widely based on the cold
chain. Even though temperatures lower than optimum
decrease growth rates in all bacteria, growth inhibition
of L. monocytogenes is not complete until temperature
is below 0°C (Markkula, 2013).
Food safety is one of the leading issues for the
agricultural industry, for both livestock and producers
of the property that are influencing consumer demand
for meat products, and therefore, microbiological safety
is considered as very important factor. Listeriosis is
one of the important emerging food-borne bacterial
zoonotic diseases of worldwide distribution (Pal, 2007;
Gebretsadik et al., 2011; Kumar, 2011; Pal and
Mahendra, 2015). It affects mainly the infants,
pregnant women, elderly, and immunocompromised
individuals (Pal, 2015). It is associated with the highest
case fatality rate of 30% approximately, unlike
infection with other common food-borne pathogens
(Khan et al., 2013).
Information on the occurrence and distribution
of L. monocytogenes and other Listeria species is very
limited both in the veterinary and public health sectors
in Ethiopia (Gebretsadik et al., 2011). In developing
countries, there have been very few or no reports on L.
monocytogenes. This might be true because no one has
given it due attention or were unaware of its occurrence
(Molla et al., 2004). The present study was
contemplated with the objectives to determine the
prevalence of Listeria monocytogenes in meat of sheep,
to conduct the antibiotic susceptibility of the isolates of
L. monocytogenes from sheep meat, and to elucidate
the risk factors, and the public health implications of L.
monocytogenes in butchers and meat handlers.
2. Materials and Methods
2.1 Study Area
The study was carried out in Addis Ababa
Central Ethiopia. Addis Ababa is the capital city of
Federal Democratic Republic of Ethiopia, and it has an
area of 51,000 hectare in the central highlands with an
average altitude of 2000-2560 meters above sea level.
The area is characterized by bimodal rainfall with an
average of 1100 mm, the highest percentage of rain
falls during the long rainy season from June to
September. The short rainy season is from February to
April. Addis Ababa has an estimated human population
of 3.15 million (CSA, 2007).
2.2 Study Abattoir and Origin of Samples
Addis Ababa Abattoir Enterprise was
established before 65 years ago, and is located at the
heart of Addis Ababa. The abattoir has different
components such as slaughter hall, chilling room,
detention meat room, condemned meat room, hide and
skin room, veterinary office, water supply (cold and
warm), electric generator, vehicles and incinerator. The
abattoir has six separate slaughter halls, three for
bovine, two each for ovine and caprine, and one for
swine. The abattoir is a high output abattoir in the
country providing 50% of the daily beef requirements
of the city’s residents. Most of the cattle slaughtered at
the abattoir are adult males of local Zebu, through
lesser numbers of crossbred males, calves as well as
culled dairy cows. Species of animals slaughtered
included bovine, ovine, caprine, and swine (CSA,
2007). In the abattoir, regular meat inspection is being
conducted by meat inspector as well as veterinarians
from Ministry of Agriculture. The abattoir has both
clean and dirty areas, so that after skinning and
evisceration, carcass follows the clean lines until
inspection and transporting while those offal, skin etc,
to dirty areas as by product preparation, like pet animal
feeds, hide, and skin for sale as well as, those unfit
ones and condemned organs to incinerators for burning
(CSA, 2007).
The swab samples were collected aseptically
from sheep meat from Addis Ababa Abattoir Enterprise
and butcher shops located in the city. In addition,
swabs were also collected from equipments like knives,
cutting tables, and hooks.
2.3 Study Population and Sample Size
Determination
The study population represented sheep meat
and equipments such as knives, cutting tables, and
hooks. The approximate sample size required was
determined from expected prevalence of 50% with
defined precision of 5% and level of confidence of
95% (Thrusfield, 2005).
n =1.96
2
Pexp (1-Pexp)
d
2
Where, n = required sample size
Pexp = expected prevalence
d = desired absolute precision
Mulu and Pal…Studies on the Prevalence, Risk Factors, Public Health Implications and Antibiogram of Listeria
monocytogenes in Sheep Meat Collected from Municipal Abattoir and Butcher Shops in Addis Ababa
Journal of Foodborne and Zoonotic Diseases | January-March, 2016 | Vol 4 | Issue 1 | Pages 01-14
© 2016 Jakraya Publications (P) Ltd 3
Therefore, by using estimated prevalence of
50% in raw meat of sheep and taking a confidence
interval of 95% and 5% absolute precision, the
minimum sample size required for this study was 768
sheep meat swab samples. A total of 873 samples
comprising of 384 sheep meat swabs from the butcher
shops, 384 sheep meat swab from the Addis Ababa
Abattoir Enterprise were used for the study. In
addition, 105 swabs were also obtained from
equipments like knives, cutting tables and hooks (Table
1).
Table 1: Distribution of the type and number of
samples collected
Type of sample Number of samples
Sheep meat swabs 768
Knives 40
Cutting tables 45
Hooks 20
Total 873
2.4 Study Design
A cross-sectional study was conducted to
determine the prevalence of L. monocytogenes and
antibiotic susceptibility test from September 2013 to
May 2014 in sheep meat slaughtered at Addis Ababa
Abattoir Enterprise, and meat presented for sale in
different butcher houses in the city. Each sample was
brought at the Food Microbiology Laboratory of
Ethiopian Public Health Institute (EPHI), Addis Ababa,
Ethiopia. On each sampling day, all the required
samples (sheep meat swab sample, knives, cutting
tables, and hooks) were taken for isolation of the
bacterium.
2.5 Sampling Techniques
In Addis Ababa Municipal Abattoir, the
maximum numbers of animals are slaughtered on
Wednesday and Friday, and mainly during holidays.
Carcasses were examined just after evisceration before
washing. The meat was swabbed without distinction of
race, sex or age at Addis Ababa Abattoir Enterprise,
and different butcher shops during several visits. The
carcasses were chosen in a systematic random
sampling method and examined just after the stage of
evisceration. And for the butcher shops, convincing
sampling type was performed, and the samples were
taken only from the sites where they were sold to the
consumers.
All samples were collected aseptically using
disposable gloves to avoid contamination, and the
samples were labeled with necessary information
including the date of sampling, sample code and
sample type. The selected meat was swabbed
aseptically using the method described in ISO11290-1
(1996) by placing sterile template (10 x 10 cm) on
specific sites of a carcass. A sterile cotton tipped swab
(2x3 cm) fitted with shaft, was first soaked in an
approximately 10 ml of buffered peptone water (Oxoid
Ltd., Hampshire, England) rubbed first horizontally,
and then vertically several times on the carcasses. The
abdomen (flank), thorax (lateral), crutch, and breast
(lateral), which were sites with the highest rate of
contamination, was chosen for sampling. On
completion of the rubbing process, the cotton swab was
left in the test tube. Finally, the carcass swabs taken
was kept in a transport medium (buffered peptone
water), and transported to the Food Microbiology of
Ethiopian Public Health Institute (EPHI), Addis Ababa,
Ethiopia for microbiological analysis. Up on arrival,
the samples were stored in refrigerator at 4°C.
2.6 Isolation and Identification of Listeria
monocytogenes
The techniques recommended by the French
Association for Standardization (AFNOR,1993) and
International Standards Organization (ISO 11290-1,
1996) were employed for the isolation and
identification of L. monocytogenes.
2.6.1 Primary Selective Enrichment
Each sample kept in buffered peptone water was
mixed thoroughly to ensure the homogeneity of its
contents, and about 0.1 ml was obtained aseptically
into 10 ml of prepared Listeria Enrichment Broth
(LEB) followed by mixing, and the sample was kept in
the incubator and incubated at 30
o
C for 48 hrs.
2.6.2 Secondary Selective Enrichment
The secondary selective enrichment medium
with full concentration of selective agents was
employed. From the pre-enrichment culture (Listeria
Enrichment Broth), after being well mixed 0.1 ml was
transferred into 10 ml of Half Fraser broth, and was
incubated at 35°C for 24 hours.
2.6.3 Isolation and Identification
From Half Fraser Broth showing black color, a
loopful of the culture was streaked onto PALCAM agar
plates and OXA agar plates and incubated at 37
o
C for
24 to 48 hours. Identification of Listeria species on
PALCAM agar plates was based on aesculin hydrolysis
and mannitol fermentation. All Listeria species
hydrolysed aesculin as evidenced by a blackening of
the medium. Mannitol fermentation was demonstrated
by a color change in the colony and/or surrounding
medium from red or gray to yellow due to the
production of acidic end products. The selectivity of
the PALCAM medium is achieved through the
Mulu and Pal…Studies on the Prevalence, Risk Factors, Public Health Implications and Antibiogram of Listeria
monocytogenes in Sheep Meat Collected from Municipal Abattoir and Butcher Shops in Addis Ababa
Journal of Foodborne and Zoonotic Diseases | January-March, 2016 | Vol 4 | Issue 1 | Pages 01-14
© 2016 Jakraya Publications (P) Ltd 4
presence of lithium chloride, polymixin B sulphate, and
acriflavine hydrochloride present in the medium base
and ceftazidime provided by PALCAM antimicrobial
supplement. These agents effectively suppress the
growth of most commonly occurring non-Listeria
species of bacteria present in food samples. On
PALCAM agar, typical colonies were grey-green with
a black sunken center and a black halo, and on Oxford
agar, colonies appeared brown black or greenish black
with a depressed center and a surrounding black halo.
2.6.4 Confirmation
Colonies suspected to be Listeria was
transferred onto Tryptose yeast extract agar plate
(TSYEA), and incubated at 37
o
C for 18 to 24 hours.
The colonies assumed to be Listeria were characterized
by using Gram’s staining, characteristics of hemolysis,
carbohydrate utilization, and CAMP (Christie Atkins
Munch Peterson) test following standard methods
(AFNOR, 1993; ISO 11290-1, 1996).
The CAMP test was undertaken using
Staphylococcus aureus (CIP: Collection of Institute of
Pasteur, 5710). It was streaked vertically in a single
line across a sheep blood agar plate and Listeria
isolates horizontally to S. aureus streak. The plates
were incubated at 37
o
C for 18 to 24 hours. An
enhanced zone of beta hemolysis between the test
strain and culture of S. aureus was considered a
positive reaction (ISO 11290-1, 1996). L.
monocytogenes showed an enhanced zone of
hemolysis, forming a narrow head towards the culture
of S. aureus. For the carbohydrate utilization test,
single isolated colony from TSYEA was transferred
into test tubes containing xylose, rhamnose, and
mannitol, and incubated at 37
o
C for up to 5 days.
Positive reactions were indicated by yellow color (acid
formation).
2.7 Antimicrobial Susceptibility Testing
Antimicrobial susceptibility tests were
performed for L. monocytogenes and other Listeria
isolates by using Muller Hinton Agar. The common
conventional antimicrobial drugs such as amoxyclav,
chloramphenicol, ampicillin, streptomycin,
tetracycline, vancomycin, ciprofluxcin, gentamicin,
sulfamethtrimethoprin, penicillin, co-trimexazole,
oxacillin, and clindamycin were tested. The method
applied for antimicrobial testing was agar plate
antibiotic disk diffusion method, using Kirby-Bauer
technique by 0.5 McFarland Standard (Mac Gowan et
al., 1990; Antunes et al., 2002; Hansen et al., 2005).
Two pure colonies of the isolate was taken from the
tryptone yeast extract agar and suspended in Muller
Hinton Broth (MHB) and then, incubated at 37
o
C for 1-
2 hrs. The suspension was checked for the development
of slight turbidity. It was inoculated, by dipping a
sterile cotton swab into it and wiping on the Muller
Hinton agar, according to the standard procedure
(NCCLS), and then the antimicrobial discs was firmly
placed on it, and the plates were incubated at 37
o
C for
24 hrs. The results were interpreted in accordance with
the criteria of the Clinical and Laboratory Standards
Institute (CLSI, 2004). The resistance profile of the
strains was reported according to the abbreviation for
the antibiotics to which they showed resistance.
2.8 Questionnaire Survey
Questionnaire survey was conducted to the meat
value chains in the study sites, and a detailed and
organized questionnaire format was designed. A
structured questionnaire were prepared and pre-tested;
and 50 butchers and 50 abattoir workers were
surveyed. The questions and answers were written in
English.
2.9 Data Management and Analysis
The data obtained through questionnaire survey,
and laboratory results of the samples were entered into
databases using Microsoft Excel computer program and
analyzed using SPSS version 20 statistical computer
software programs. Descriptive statistics were used to
describe the nature and the characteristics of the data.
Comparisons between the prevalence of groups were
analysed by using Chi-square (χ
2
) test. For all tests, p-
value less than 0.05 were considered to be significant.
3. Results
3.1 Prevalence of Listeria monocytogenes in
Abattoir and Butcher Shops
From a total of 873 samples examined, the
overall prevalence of L. monocytogenes was recorded
4.1% (Fig 2). The prevalence rate of L. monocytogenes
varied between sample sources. Out of each 384
samples collected from the abattoir and butcher shops,
the prevalence of L. monocytogenes were 2.1%, and
5.5%, respectively. The result was higher in butcher
shops than abattoir, and there was significant difference
in the prevalence of L. monocytogenes from these
sources of samples (p<0.05) (Table 3). Out of 105
equipment samples obtained from both abattoir and
butcher shops, the prevalence of L. monocytogenes was
6.7%. There was no significant difference in the
prevalence of L. monocytogenes both in case of abattoir
and butcher shops (p>0.05).
An overall prevalence (4.1%) of L.
monocytogenes was demonstrated in different sample
sources when they were analyzed together (Table 2).
Cutting table was found to have the highest prevalence
Mulu and Pal…Studies on the Prevalence, Risk Factors, Public Health Implications and Antibiogram of Listeria
monocytogenes in Sheep Meat Collected from Municipal Abattoir and Butcher Shops in Addis Ababa
Journal of Foodborne and Zoonotic Diseases | January-March, 2016 | Vol 4 | Issue 1 | Pages 01-14
© 2016 Jakraya Publications (P) Ltd 5
Table 2: Overall prevalence of Listeria monocytogenes from different source of samples
Sample type No. Examined Prevalence (%) 95 % CI
Abattoir 384 8 (2.1) a 0.1-4.1
Butcher 384 21(5.5) ab 3.5-7.5
Cutting table 45 4 (8.9) ab 3.1-14.7
Hook 20 (0.0) b -
Knife 40 3 (7.5) a 1.3-13.7
Total 873 36 (4.1) -
*
ab
Proportions (%) with similar letters are not statistically significant (with p-value = 0.05),
CI= Confidence interval; %= Percent of prevalence
Table 3: Prevalence of Listeria monocytogenes from different sources of samples
Source of
sample No. of
examined Prevalence
(%) OR CI of
OR χ
2
p-value
Abattoir 384 8 (2.1) 1 - - -
Butcher 384 21 (5.5) 2.7 1.2-6.2 6.1 0.02
Total 768 29 (3.8) - - - -
OR= odds ratio; CI= confidence interval; χ
2
= Chi square
Fig 1: Map of Addis Ababa, the capital of Ethiopia
(8.9%) followed by knife (7.5%) (Fig 2). The least
prevalence was found in hook (0.0%) that had
statistically significant difference comparing with the
others items. Though there was difference in the
prevalence among the others samples (abattoir, butcher,
cutting table, and knife), it was not statistically
significant.
3.2 Prevalence of Listeria monocytogenes in
Abattoir and Butcher shops
Mulu and Pal…Studies on the Prevalence, Risk Factors, Public Health Implications and Antibiogram of Listeria
monocytogenes in Sheep Meat Collected from Municipal Abattoir and Butcher Shops in Addis Ababa
Journal of Foodborne and Zoonotic Diseases | January-March, 2016 | Vol 4 | Issue 1 | Pages 01-14
© 2016 Jakraya Publications (P) Ltd 6
Out of 768 swab samples examined during the
study period, 29 (3.8%) i.e. 8 (2.1%) from abattoir and
21 (5.5%) from butchers were positive for L.
monocytogenes. The total prevalence of L.
monocytogenes from abattoir and butcher shops was
3.8% (N=768). The prevalence in butcher was higher
with statically significant difference (P=0.02). The
prevalence of the bacterium in butcher houses was
almost three times (OR= 2.7, CI= 1.2-6.2) higher than
the causative agent identified from abattoir. It is also
indicated in the figure below (Table 3, Fig 3).
3.3 Contamination Rate of Listeria
monocytogenes in Equipments
The contamination rate of L. monocytogenes in
meat surface contact materials (hook, knife and cutting
table) is presented in Table 4. Although there was not
even one sample positive for hooks (Fig 3), there was
no statistically significant difference among hook,
knife, and cutting table (P= 0.2).
3.4 Antimicrobial Susceptibility
A total of 36 isolates of L. monocytogenes were
tested for antimicrobial susceptibility. All isolates of L.
monocytogenes were susceptible to amoxyclav. Out of
36 isolates, 28 (77.8%) were resistant to tetracycline,
and 9 (25%) were resistant to penicillin. Four (11.1%)
were equally resistant to streptomycin and ampicillin, 7
(19.4%) were equally resistant to sulfamethoprim and
oxacillin, 2 (5.6%) were equally resistant to
clindamycin and vancomycin. Interestingly, 34 (94.1%)
isolates of L. monocytogenes were equally susceptible
to vancomycin, and co-trimexasole. The details of
susceptibility pattern of the isolates are presented in
Table 5. The study also revealed multi-drug resistance
isolates in 10/36 (22.7%), 13/36 (36.1%), and 24/36
(66.7%) for one, two, and two or more drug
antimicrobials, respectively.
3.5 Findings of Questionnaire Survey
3.5.1 Findings of Questionnaire Survey in Abattoir
A total of 50 respondents were surveyed from
the abattoir. About 60% of the abattoir workers had
completed high school level. Out of 50 respondents, all
(100%) had taken a lesson on personal hygiene. About
56% and 36% of respondents washed their hands once,
and twice per day during the course of working time,
respectively. Interestingly, 74% of the respondents
reported the use of detergent. Most of the respondents
(92%) washed their hands after the use of toilet. All
(100%) of the respondents cleaned the working
surfaces between each process and after the work.
About 80% of the respondents washed their working
knives after the completion of the work, and the rests
washed several times during the course of working
time. As on observational assessment, 76% of the
closets of butchers were dirty. Almost all of the
workers in the working room wore aprons and put a
hair covering. Approximately, 78% of them did not
wear any jewelry. Regarding the hygienic status of the
abattoir, it was in a medium status.
3.5.2 Findings of Questionnaire Survey in
Butcher Shops
A total of 50 respondents were surveyed from
butcher shops. About 48% of the butchers were in an
educational level of elementary, and 38% had
completed high school level. Approximately, 50% of
the respondents had taken a lesson on personal
hygiene. About 46% and 36% of the respondents
washed their hands twice and once per day during the
course of working time, respectively. It was interesting
to note that 86% of the respondents reported to use a
detergent. As observed during the current study, about
96% of the respondents washed their hands after toilet.
About 38% of the respondents reported that the
cashier was handling the money. The majority (62%)
of the respondents handled the money by themselves.
Most of the butchers (72%) cleaned the working
surfaces, and washing of knives after work was
performed by 7.8% of the butchers. As on
observational assessment, 60% of the closet of the
butchers was dirty. Most of them (74%) did not wear a
hair covering. Wearing of jewelry was observed in
38% of the butchers. About the hygienic status of the
butcher shops, 50%, 30% and 20% had poor, moderate,
and good status, respectively.
4. Discussion
Listeria species are ubiquitous in nature, and
have been isolated from wide environmental sources
(Liu, 2008; Raorane et al., 2014; Pal, 2015). The
organism possesses ability to survive in harsh
conditions and therefore, can persist in the
environment. Because of such persistence, Listeria
species can easily enter in the food chain. Of the
known Listeria species, L. monocytogenes is
pathogenic to humans and animals (Pal, 2007; Raorane
et al., 2014). The organism is sensitive to the
antibiotics such as ampicillin, erythromycin, and
penicillin but showed resistance to cephalosporines,
fluroquinolones, and tetracycline (Pal, 2015).
Raw meat and other raw food products
commonly found in the retail environment may be
contaminated with pathogens, including L.
monocytogenes. Retail environments are much more
open with many people coming and going. These open
retail environments may allow for the introduction of
L. monocytogenes at various points and times of the -
Mulu and Pal…Studies on the Prevalence, Risk Factors, Public Health Implications and Antibiogram of Listeria
monocytogenes in Sheep Meat Collected from Municipal Abattoir and Butcher Shops in Addis Ababa
Journal of Foodborne and Zoonotic Diseases | January-March, 2016 | Vol 4 | Issue 1 | Pages 01-14
© 2016 Jakraya Publications (P) Ltd 7
Fig 2: Overall prevalence of Listeria monocytogenes
Fig 3: Proportion of positive prevalence in abattoir and butcher shops
Mulu and Pal…Studies on the Prevalence, Risk Factors, Public Health Implications and Antibiogram of Listeria
monocytogenes in Sheep Meat Collected from Municipal Abattoir and Butcher Shops in Addis Ababa
Journal of Foodborne and Zoonotic Diseases | January-March, 2016 | Vol 4 | Issue 1 | Pages 01-14
© 2016 Jakraya Publications (P) Ltd 8
Table 4: Prevalence of Listeria monocytogenes in meat contact surface materials
Source of
sample No. of
examined Total
positive Prevalence
(%) χ
2
p-value
Hook 20 0 0.00 - -
Knife 40 3 3 (7.5) 3.1 0.2
Cutting table 45 4 4 (8.9) - -
Total 105 7 7 (6.7) - -
Table 5: Susceptibility of Listeria monocytogenes isolates to different antimicrobials
Antimicrobial Listeria monocytogenes
S R I
N (%) N (%) N (%)
Ampicillin 32 (88.9) 4 (11.1) 0
Chloramphenicol 32 (88.9) 3 (8.3) 1 (2.8)
Ciprofloxacin 28 (77.8) 7 (19.4) 1 (2.8)
Penicillin 24 (66.7) 9 (25) 3 (8.3)
Tetracycline 04 (11.1) 28 (77.8) 4 (11.1)
Vancomycin 34 (94.4) 2 (5.6) 0
Co-trimexazole 34 (94.4) 2 (5.6) 0
Streptomycin 30 (83.3) 4 (11.1) 2 (5.6)
Gentamycin 35 (97.2) 1 (2.8) 0
Amoxyclav 36 (100) 0 0
Clindamycin 29 (80.5) 2 (5.6) 5 (13.9)
Sulfamethrimethoprim 24 (66.7) 7 (19.4) 5 (13.9)
Oxacillin 28 (77.8) 7 (19.4) 1 (2.8)
S= Susceptible; R= Resistant; I= Intermediate
day, potentially making control of L. monocytogenes in
the retailed environment more difficult (Cutter et al.,
2006). The detection and identification of Listeria
species have attracted the attention of many
researchers. This specific interest is related to the
presence of L. monocytogenes, one of the most
important food-borne pathogens, in the genus Listeria.
It is often found in various raw foods, such as
uncooked meat, and vegetables, as well as in processed
foods that become contaminated after processing like
soft cheese and cold cuts (Pal, 2015). It is widely
diffused in the environment, and this fact can cause the
contamination of food during production and
distribution (Cocolin et al., 2002).
In the present study, L. monocytogenes was
isolated from 36 of 873 samples, giving a prevalence
rate of 4.1%. The specific prevalence of L.
monocytogenes based on sample sources was found to
be statistically significant. The prevalence of L.
monocytogenes in sheep meat at abattoir and butchers
shops was 3.8. Our results seem to be in agreement
with the observations of Pociecha and co-workers
(1991) and Ankpolat and others (2004) who noted a
prevalence of 3.2% and 5% from ovine carcass in New
Zealand and Turkey slaughter houses, respectively.
Molla et al. (2004) have demonstrated a prevalence of
5.1% in raw and ready-to-eat food products. The higher
prevalence of 30% and 40% of L. monocytogenes was
recorded by Mac Gowan et al. (1994) and Gilbirt et al.
(2009), respectively. The prevalence of 4.0% of L.
monocytogenes from gall bladder of sheep in slaughter
house was recorded by Al-Ali et al. (2012). Several
Mulu and Pal…Studies on the Prevalence, Risk Factors, Public Health Implications and Antibiogram of Listeria
monocytogenes in Sheep Meat Collected from Municipal Abattoir and Butcher Shops in Addis Ababa
Journal of Foodborne and Zoonotic Diseases | January-March, 2016 | Vol 4 | Issue 1 | Pages 01-14
© 2016 Jakraya Publications (P) Ltd 9
Fig 4: The positive proportion of the surface materials to Listeria monocytogenes
Fig 5: Multidrug resistance in Listeria monocytogenes for selected antimicrobial agents
studies confirmed that a prevalence of 4% by Ndahi et
al. (2013) in ready- to- eat foods, 2.4% by Ennaja et al.
(2008) from meat and meat products, and 4.7% by
Yucel et al. (2005) from meat products. On the
contrary, there was no isolation of L. monocytogenes at
abattoir from sheep meat in Germany (Cohen et al.,
2006). The prevalence of L. monocytogenes in meat
samples differ from country to country. The reasons of
low and high prevalence rates may be attributed to
differences in hygienic conditions of slaughter houses,
storage, and processing in various countries.
The specific prevalence of L. monocytogenes
from equipments was found to be statistically not
significant. Dirty or contaminated equipments can
contaminate the safe food. Improperly cleaned
equipment can be a source of L. monocytogenes
contamination. Based on FDA reports and food-borne
outbreak reports provided to the CDC, three risk
factors have been identified most frequently as
contributing to the contamination, spread and growth of
food-borne pathogens, including L. monocytogenes, in
processing or retail environments. These are cross-
contamination, improper cleaning and sanitation, and
improper time and temperature control (Cutter et al.,
2006; Pal and Mahendra, 2015).
In our study, the equipments were identified as
the potential source of contamination of meat with a
prevalence of 6.7% of L. monocytogenes, which was
lower than the findings of Lowry and Tiong (1988)
who recorded 13% prevalence of L. monocytogenes in
Mulu and Pal…Studies on the Prevalence, Risk Factors, Public Health Implications and Antibiogram of Listeria
monocytogenes in Sheep Meat Collected from Municipal Abattoir and Butcher Shops in Addis Ababa
Journal of Foodborne and Zoonotic Diseases | January-March, 2016 | Vol 4 | Issue 1 | Pages 01-14
© 2016 Jakraya Publications (P) Ltd 10
Table 6: Summary of observational assessment and knowledge of workers on hygienic practices in abattoir
Abattoir activity Performance No.of respondents Percent
Educational status 1-4
5-8
9-12
5
15
30
10
30
60
Lesson on personal hygiene Yes
No 50 100
Time interval of washing hands Once
Twice
Other
28
18
4
56
36
8
Washing of hands With water only
With detergent 13
37 26
74
Washing of hands after toilet Yes
No 46
4 92
8
Clean and disinfect working surfaces Before work
Between each process 0
50 0
100
Washing of knives After work
Between process 40
10 80
20
View of closets Neat
Dirty 12
38 24
76
Wearing of aprons Yes
No 50
0 100
0
Hair Covered
Not covered 50
0 100
0
Wearing of jewelry Worn
Not worn 11
39 22
78
food contact surfaces. Therefore, control measures to
reduce the carriage of the pathogens in ruminants prior
to slaughter should be reviewed with reference to the
current regulations and guidelines relating to the
primary production. A higher prevalence (25.64%) of
L. monocytogenes in other country was reported by
Jankuloski et al. (2007). The variation of prevalence in
the two study sites may be because of environmental
contamination, and poor sanitary conditions while
handling of the meat before it reached to the consumer.
The contamination occurs in an increasing level along
the food value chain starting from slaughtering at the
abattoir level, during distribution of the meat, and
improper handling of the meat handlers who sold it.
Antibiotic resistant bacteria pose a growing
problem of concern, worldwide since the bacteria can
be easily circulated in the environment. Effectiveness
of current treatments and ability to control infectious
diseases in both animals and humans may become
hazardous. A relatively high number of strains are
resistance to the antimicrobials commonly used in the
therapeutic protocols of many humans and animals
infections (Normanno et al., 2007). In the current
study, a resistance for tetracycline was 77.8%. On the
contrary, 0% resistance was reported by Conter et al.
(2013). Findings of resistant as well as poly-resistant
strains of L. monocytogenes to antimicrobial drugs
were rather sporadic. It is pertinent to mention that
such strains isolated from foods, were frequently found
resistance to tetracycline and penicillin (Navratilova et
al., 2004).
In this study, our results regarding tetracycline
resistance for L. monocytogenes was higher than the
previous findings of Gupta and Sharma (2013) who
observed 25%. However, in case of amoxyclav, we
found 100% isolates of L. monocytogenes sensitive.
This observation was lower than the results of Gupta
and Sharma (2013 who reported 75% sensitivity. Thus,
the resistance figures from different countries can
considerably vary from very low to very high, probably
reflecting the use of antimicrobials in those countries.
Except tetracycline and penicillin, most antimicrobial
Mulu and Pal…Studies on the Prevalence, Risk Factors, Public Health Implications and Antibiogram of Listeria
monocytogenes in Sheep Meat Collected from Municipal Abattoir and Butcher Shops in Addis Ababa
Journal of Foodborne and Zoonotic Diseases | January-March, 2016 | Vol 4 | Issue 1 | Pages 01-14
© 2016 Jakraya Publications (P) Ltd 11
Table 7: Summary of observational assessment and knowledge of workers on hygienic practice in butcher shops
Questionnaire and observation type Performance No. of respondents Percent
Educational status 1-4
5-8
9-12
7
24
19
14
48
38
Lesson on personal hygiene Yes
No 25
25 50
50
Time interval of washing hands Once
Twice
Other
18
23
9
36
46
18
Washing of hands With water only
Water and detergent 7
43 14
86
Washing of hands after toilet Yes
No 48
2 94
6
Handling money Cashier
Butcher 19
31 38
62
Cleaning working surfaces Before work
After work 14
36 28
72
Washing of knives After work
Between each selling 39
11 78
22
View of closets Neat
Dirty 20
30 40
60
Hair covering Covered
Not covered 13
37 26
74
Wearing of jewelry Worn
Not worn 19
31 38
62
Hygienic status of the butcher house Good
Moderate
Poor
10
15
25
20
30
50
drugs tested during this study effectively prevented the
growth of L. monocytogenes.
The current study revealed that chloramphenicol
resistance was found to be 8.3%, which was lower than
the findings of Gupta and Sharma (2013) who reported
50%. It is worth mentioning that L. monocytogenes
isolates examined in this study from all types of
samples were resistant to 19.4% and 77.8%. On the
contrary, percentages of resistance to ciprofloxacin and
tetracycline were 1.8%, and 9%, respectively as
reported by Zhang (2005). In the current study,
resistance for ampicillin was observed 11.1%. We
found multidrug resistance in L. monocytogenes.
Similarly, workers from other countries also reported
multidrug resistance (Zhang, 2005; Gupta and Sharma,
2013).
A larger sample size is needed to determine if
there are differences between antimicrobial resistance
patterns of the isolates among different sample sources.
Considering that L. monocytogenes is slowly becoming
antibiotic resistant, a continued surveillance of
emerging antimicrobial resistance of this pathogen is
important for effective treatment (Conter et al., 2009).
As drug resistance is a growing public health concern,
sincere attempts are needed to mitigate this problem.
Contamination of foods by L. monocytogenes
can occur in all the steps from farm to table, which
emphasizes the need to put forward control measures at
every step. This can happen at retail level. During
processing, the source of contamination can be
surfaces, equipment, and workers, and persistence of
strains has been detected at retail level. Employees can
Mulu and Pal…Studies on the Prevalence, Risk Factors, Public Health Implications and Antibiogram of Listeria
monocytogenes in Sheep Meat Collected from Municipal Abattoir and Butcher Shops in Addis Ababa
Journal of Foodborne and Zoonotic Diseases | January-March, 2016 | Vol 4 | Issue 1 | Pages 01-14
© 2016 Jakraya Publications (P) Ltd 12
contaminate food with L. monocytogenes if proper
personal hygiene policies are not followed or if
employees do not take the proper steps to safely
receive, store, prepare, and serve food. They also may
be a source for L. monocytogenes since some humans
are known to carry the pathogen in their
gastrointestinal tracts. Poor personal hygiene practices,
such as improper hand washing or dirty uniforms, can
lead to the contamination of food and equipment with
L. monocytogenes (Cutter et al., 2006).
Proper motivation, education, and training of
employees and managers in food industries are vital to
keep consumers safe against food-borne diseases (Pal
and Mahendra, 2015). In this study, 100% of the
respondents from the abattoir had taken a lesson on
personal hygiene but from the butcher shops, only 50%
of the respondents had taken a lesson on personal
hygiene. Therefore, all currently available educational
approaches need to be critically evaluated and adopting
of employees training to minimize L. monocytogenes
cross contamination (Crandal et al., 2011).
Furthermore, 92% of the abattoir workers, and 96% of
the butchers washed their hands after the use of toilet.
In contrary, few workers did not wash their hands. This
may contribute to a low level of contamination of meat.
One previous study revealed a prevalence of 16.7% and
27.8% from smoked and cooked meat products and
from fermented dry meat products, respectively
(Navratilova et al., 2004).
The results of this study showed that most of the
respondents (74% of abattoir workers and 86% of
butchers) used a detergent for washing of hands.
Findings of L. monocytogenes in swabs from
equipments and working surfaces witnessed the fact
that contamination of meat and meat products is due to
secondary soiling from the environment or equipment
of meat-processing plants. Contamination generally
increased during cutting, probably as a result of cross
contamination. Also, in the retail and food service
environment, contamination may be transferred
between ready-to-eat products (Lianou and Sofos,
2007). The type of handling that ready-to-eat meat
receives may also influence the level of L.
monocytogenes contamination. In a survey of retail
packaged meats, there was a significantly higher
prevalence of L. monocytogenes reported in products
cut into cubes (61.5% out of 13) compared with sliced
products (4.6% out of 196) (Angelidis and
Koutsoumanis, 2006).
5. Conclusion
The consumption of improper meat is not safe
from consumer point of view, as it may lead to the
transmission of various diseases. In this study, the
results of bacteriological assessment showed that raw
meat from market and slaughter houses are a source of
L. monocytogenes. In addition, the presence of this
bacterium may be attributed to the unclean working
environment, poor sanitary conditions of persons who
are contacting with the meat and the equipments. This
may result in low meat quality and might potentially
cause food poisoning, especially in susceptible groups,
which include pregnant women, children, elderly, and
immunosuppressed persons. Due to high risk and
public health concern, it may cause a high case fatality
rate. The detection of this pathogen in ready to eat
processed food makes it unfit for human consumption.
Listeria monocytogenes may not be seen as
potential clinical threat in Ethiopia today, with the
increasing trend of transnational spread and emerging
diseases. The probable risk that it might pose in the
years to come cannot be ignored. The present study
demonstrated the possible risk of L. monocytogenes
after consuming meat and ready-to eat food stuffs
available in the markets, and also highlighted the need
for an effective and efficient storage process to keep
such food safe, till they reached the consumers.
Numerous risk factors are associated with the
contamination and growth of L. monocytogenes in
abattoir and market places. These factors need to be
addressed and considered a serious hazard to identify
control measures for an effective prevention and
control program of this emerging food-borne pathogen.
Further, the sources of infection and modes of
transmission should be ascertained. In addition,
addressing communication, risk perception and
consumer practices to the public are mandatory.
The present study revealed widespread
resistance by L. monocytogenes to commonly used
antimicrobials. In addition, the prevalence of multi-
drug resistance of the bacterium is also phenomenon,
which gives cause for serious concern. In order to
detect early changes in bacteria susceptibilities before a
high prevalence of resistance is developed, regular
monitoring of antimicrobial resistance to pathogenic
bacteria should be practiced. The genetic mechanisms,
which mediate antimicrobial resistance in this
bacterium, would also need further studies.
Acknowledgements
We are thankful to Dr. Asefa Deressa and
Madam Firehiwot Abera for helping us to work in The
Ethiopian Institute of Public Health, Addis Ababa,
Ethiopia. Thanks are also due to the Addis Ababa
Abattoir Enterprise, butchers shops, and workers for
their kind help and cooperation during this study.
Mulu and Pal…Studies on the Prevalence, Risk Factors, Public Health Implications and Antibiogram of Listeria
monocytogenes in Sheep Meat Collected from Municipal Abattoir and Butcher Shops in Addis Ababa
Journal of Foodborne and Zoonotic Diseases | January-March, 2016 | Vol 4 | Issue 1 | Pages 01-14
© 2016 Jakraya Publications (P) Ltd 13
References
AFNOR (1993). Food Microbiology. French Association for
Standardization, Paris, France. Pp. 8-55.
Akpolat NO, Elci S, Atmaca S and Gul K (2004). Listeria
monocytogenes in products of animal origin in Turkey.
Journal of Veterinary Research Communication, 28:
561-567.
Al Ali HGK, Alrodham MA and Almohana AM (2012).
Isolation of Listeria monocytogenes from gallbladder of
sheep and cattle in slaughter house Najaf. Kufa Journal
of Veterinary Medical Sciences, 3: 1-8.
Angelidis AS and Koutsoumanis K (2006). Prevalence and
concentration of Listeria monocytogenes in sliced
ready-to-eat meat products in the Hellenic retail market.
Journal of Food Protection, 69: 938-942.
Antunes P, Reu C, Jousa JC, Pestana N and Peixe L (2002).
Incidence and susceptibility to antimicrobial agents of
Listeria species and Listeria monocytogenes isolated
from poultry carcasses in Porto, Portugal. Journal of
Food Protection, 65: 1883-1893.
CLSI (2004). Performance Standards for antimicrobial disk
and dilution susceptibility test for bacteria isolated from
animals, Approved standard, 2
nd
Ed. Clinical and
Laboratory Standards Institute, Wayne, Pennsylvania,
Vol. 22, No. 6, M31-A2.
Cocolin L, Rantsiou K, Iacumin L, Cantoni C and Comi G
(2002). Direct identification in food samples of Listeria
spp. and Listeria monocytogenes by molecular
methods. Journal of Applied and Environmental
Microbiology, 68: 6273- 6282.
Cohen N, Ennaji H, Hassar M and Karib H (2006). The
bacterial quality of red meat and offal in Casablanca
(Morocco). Journal of Molecular and Nutritional Food
Research, 50: 557-62.
Conter M, Paludi D, Mureddu A, Zanardi E, Ghidini S and
Ianieri A (2013). Susceptibility of Listeria
monocytogenes strains isolated from food to
antimicrobial agents. International Journal of Food
Microbiology, 148: 315-368.
Crandall PG, Neal Jr JA, Brya CAO, Murphy CA, Marks BP
and Ricke SC (2011). Minimizing the risk of Listeria
monocytogenes in retail delis by developing employee
focused, cost effective training. Journal of Agriculture,
Food and Analytical Bacteriology, 1: 159-174.
CSA (2007). Population census http:// Wikipedia.org-wiki-
Central Statistical Agency. Accessed on October 2013.
Cutter C, McElroy D and Penn S (2006). Control of Listeria
monocytogenes in retail establishments. Information
and Communication Technologies in the College of
Agricultural Sciences. The Pennsylvania State
University.USA. Pp. 1-24.
Ennaji H, Timinouni M, Ennaji M, Hassar M and Cohen N
(2008). Characterization and antibiotic susceptibility of
Listeria monocytogenes isolated from poultry and red
meat in Morocco. Journal of Infectious Drug
Resistance, 1: 45-50.
ESAP (2001). Ethiopian Society of Animal Production.
Livestock in Food Security - Roles and Contributions.
Proceedings of 9
th
Annual Conference of the Ethiopian
Society of Animal Production held in Addis Ababa,
Ethiopia, August 30-31, 2001.
Gebretsadik S, Kassa T, Alemayehu H, Huruy K and
Kebede N (2011). Isolation and characterization of
Listeria monocytogenes and other Listeria species in
foods of animal origin in Addis Ababa, Ethiopia,
Journal of Infection and Public Health, 4: 22-29.
Gilbert S, Lake R, Hudson A and Cressey P (2009). Risk
profile: Listeria monocytogenes in processed ready-to-
eat meats. New Zealand Food Safety Authority,
Contract for Scientific Services. Institute of
Environmental Science and Research Limited, New
Zealand. Pp. 1-82.
Gupta S and Sharma V (2013). Antibiotic resistance pattern
among different Listeria species isolated from mutton
and chevon. Journal of Animal Research, 3: 99-102.
Hansen J M, Gerner-Smidt P and Bruun B (2005). Antibiotic
susceptibility of Listeria moonocytogenes in Denmark
1958- 2001. APMIS, 113: 31-36.
Hassan L, Mohammed HO, McDonough PL and Gonzalez
RN (2000). A cross-sectional study on the prevalence
of L. monocytogenes and Salmonella in New York
dairy herds. Journal of Dairy Science, 83: 2441-2447.
ISO (1996). Microbiology of food and animal feeding stuffs
– Horizontal method for the detection and enumeration
of Listeria monocytogenes. International Organization
for Standardization – Part 1: Detection method.
International Standard ISO 11290-1, Geneva,
Switzerland.
Jankuloski D, Sekulovski P, Prodanov R, Musliu ZH and
Dimzovska BS (2007). Listeria monocytogenes
contamination of environment and surfaces of the
equipment in the meat processing facilities in republic
of Macedonia. Directory of Open Access Journals,
Sweden. Pp. 1-9.
Khan JA, Rathore RS and Ahmad I (2013). In vitro detection
of pathogenic Listeria monocytogenes from food
sources by conventional, molecular and cell culture
method. Brazilian Journal of Microbiology, 44: 751-
758.
Kumar R (2011). Modern trends to investigate food-borne
listeriosis. Journal of Food Technology, 9: 9-17.
Lianou A and Sofos JN (2007). A review of the incidence and
transmission of Listeria monocytogenes in ready-to-eat
products in retail and food service environments.
Journal of Food Protection, 70: 2172-2198.
Liu D (2006). Identification, subtyping and virulence
determination of Listeria monocytogenes: An important
food borne pathogen. Journal of Medical Microbiology,
55: 645-659.
Lowry PD and Tiong I (1988). The incidence of Listeria
monocytogenesin meat and in meat products-factors
affecting distribution. In “Proceedings of 34
th
International Congress of Meat Science and
Technology”. Brisbane, Australia. Pp. 528-530.
Mac Gowan AP, Bowker K, McLauchlin J, Bennett PM and
Reeves DS (1994). The occurrence and seasonal
changes in the isolation of Listeria spp. in shop bought
food stuffs, human faeces, sewage and soil from urban
sources. International Journal of Food Microbiology,
21: 325-334.
Mulu and Pal…Studies on the Prevalence, Risk Factors, Public Health Implications and Antibiogram of Listeria
monocytogenes in Sheep Meat Collected from Municipal Abattoir and Butcher Shops in Addis Ababa
Journal of Foodborne and Zoonotic Diseases | January-March, 2016 | Vol 4 | Issue 1 | Pages 01-14
© 2016 Jakraya Publications (P) Ltd 14
Mac Gowan AP, Holt HA and Reeves DS (1990). In vitro
synergy testing of nine antimicrobial combinations
against Listeria monocytogenes. Journal of
Antimicrobial Chemotherapy, 25: 561-566.
Markkula A (2013). Epidemiology and stress responses of
Listeria monocytogenes. Faculty of Veterinary
Medicine, Department of Food Hygiene and
Environmental Health, University of Helsinki, Finland.
Molla B, Yilma R and Alemayehu D (2004). Listeria
monocytogenes and other Listeria species in retail meat
and milk products in Addis Ababa, Ethiopia. Ethiopian
Journal of Health Development, 18: 208-212.
Nafisa H, Ali I, Amber F, Adnan K, Ameera Y, Khan G and
Shahana U (2010). Microbial contamination of raw
meat and its environment in retail shops in Karachi,
Pakistan. Journal of Infection in Developing Countries,
4: 382-388.
Navratilova P, Schlegelova J, Sustackova A, Napravnikova
E, Lukasova J and Klimova E (2004). Prevalence of
Listeria monocytogenes in milk, meat and foodstuff of
animal origin and the phenotype of antibiotic resistance
of isolated strains. Journal of Veterinary Medicine, 49:
243-252.
Ndahi MD, Kwaga JKP, Bello M, Kabir J, Umoh VJ, Yakubu
SE and Nok AJ (2013). Prevalence and antimicrobial
susceptibility of Listeria monocytogenes and
methicillin-resistant Staphylococcus aureus strains
from raw meat and meat products in Zaria, Nigeria.
Letters in Applied Microbiology, 58: 262-269.
Normanno G, La Salandra G, Dambrosio A, Quaglia NC,
Corrente M, Parisi A, Santagada G, Firinu A, Crisetti E
and Celano GV (2007). Occurrence, characterization
and antimicrobial resistance of enterotoxigenic
Staphylococcus aureus isolated from meat and dairy
products. International Journal of Food Microbiology,
115: 290-296.
Pal M (2007). Zoonoses. 2
nd
Ed. Satyam Publishers, Jaipur,
India.
Pal M (2013). Food safety is becoming a global public health
concern. The Ethiopian Herald, February 01, 2013, Pp.
8.
Pal M (2015). The Complete Book on Waste Treatment
Technologies. 1
st
Ed. Nirr Project Consultancy
Services, Kamala Nagar, New Delhi, India.
Pal M and Awel H (2014). Public health significance of
Listeria monocytogenes in milk and milk products.
Journal of Veterinary Public Health, 12: 1-5.
Pal M and Mahendra R (2015). Sanitation in Food
Establishments (1
st
Edn). LAP Lambert Academic
Publishing, Saarbruchen, Germany.
Pociecha J Z, Smith K R and Manderson G J (1991).
Incidence of Listeria monocytogenes in meat
production environments of a South Island (New
Zealand) mutton slaughterhouse International Journal
of Food Microbiology, 13: 321-328.
Raorane A, Doijad S, Katkar S, Pathak A, Poharkar K,
Dubal Z and Barbuddhe S (2014). Prevalence of
Listeria species in animals and associated environment.
Journal of Advances in Animal and Veterinary
Sciences, 2: 81-85.
Thrustfield M (2005). Veterinary Epidemiology (3
rd
Ed).
Blackwell Science Ltd. Cambridge, USA, Pp. 225-228.
Yucel N, Citak S and Onder M (2005). Prevalence and
antibiotic resistance of Listeria species in meat
products in Ankara, Turkey. Journal of Food
Microbiology, 22: 241-245
Zhang Y (2005). Antimicrobial resistance of Listeria
monocytogenes and Enterococcus faecium from food
and animal sources. Ph. D. Thesis, Faculty of the
Graduate School of the University of Maryland, USA.
