African Health Sciences Vol 11 Special Issue 1 August 2011S40
Antimicrobial susceptibility patterns of E. coli from clinical sources in
*Kibret M1, Abera B2
1. Department of Biology, Science College, Bahir Dar University, Bahir Dar, Ethiopia
2. Department of Microbiology, Parasitology and Immunology, College of Medicine and Health Sciences, Bahir Dar
University, Bahir Dar, Ethiopia
Background: Escherichia coli is the leading cause of urinary tract, ear, wound and other infections in humans. Increasing
rates of antimicrobial resistance among E. coli is a growing concern worldwide.
Objectives: The aim of this study was to determine the prevalence and antimicrobial susceptibility of E. coli from clinical
Method: A retrospective review of culture results of urine, ear discharge, pus swab from wounds, and eye discharge was
done. A total of 3,149 samples were analyzed for isolation and identification of bacteria and antimicrobial susceptibility
Results: E. coli was isolated from 446 (14.2%) samples. The highest isolation rate was obtained from urine samples 203
(45.5%). High resistance rates to erythromycin (89.4%), amoxicillin (86.0%) and tetracycline (72.6%) were documented.
However, significantly high degree of sensitivity rates to nitrofurantoin (96.4%), norflaxocin (90.6%), gentamicin (79.6%)
and ciprofloxacin were recorded (p<0.001). Multiple antimicrobial resistances of 74.6% and increased resistance rates to all
antimicrobials except ciprofloxacin were also recorded.
Conclusion: E. coli isolates showed high rates of resistance to erythromycin, amoxicillin and tetracycline. Nitrofurantoin,
norflaxocin, gentamicin and ciprofloxacin are considered appropriate for empirical treatment of E. coli in the study area.
Regular monitoring of antimicrobial susceptibility is recommended.
Key words: E. coli, antimicrobial susceptibility, Ethiopia
African Health Sciences 2011; 11(S1): S40 - S45
* Correspondence author
Associate Professor of Microbiology
Department of Biology, Science College
Bahir Dar University
P. O. Box 79
Bahir Dar, Ethiopia
Mobile: 251-918-780300 /251-922-267061
Escherichia coli is a common inhabitant of the human
and animal gut, but can also be found in water, soil
and vegetation. It is the leading pathogen causing
urinary tract infections1,2,3 and is among the most
common pathogens causing blood stream
infections4, wounds, otitis media and other
complications in humans5, 6. E. coli is also the most
common cause of food and water-borne human
diarrhea worldwide and in developing countries,
causing many deaths in children under the age of
Antimicrobial resistance in E. coli has been
reported worldwide and increasing rates of resistance
among E. coli is a growing concern in both developed
and developing countries8, 9. A rise in bacterial
resistance to antibiotics complicates treatment of
infections. In general, up to 95 % of cases with severe
symptoms are treated without bacteriological
investigation10. Occurrence and susceptibility profiles
of E. coli show substantial geographic variations as
well as significant differences in various populations
and environments11. In Ethiopia, a number of studies
have been done on the prevalence and antimicrobial
resistance patterns of E. coli from various clinical
sources5, 12, 13. The aim of this study was to determine
antimicrobial susceptibility of E. coli from clinical
sources at Dessie Regional Health Research
A retrospective review was done on results of
cultures of urine, ear discharge, pus swab from
wounds, and eye discharge that had been performed
African Health Sciences Vol 11 Special Issue 1 August 2011
from 2003 - 2010 at Dessie Regional Health Research
Laboratory. The sex and age of patients. As well as
E. coli isolates and antimicrobial susceptibility data
were collected from the registration records using a
standard data collection form.
Culture and identification
The specimens were collected from public and private
hospitals and health centers. As the standard
operation procedures show, clean-catch midstream
morning urine specimens are collected using sterile
wide mouth glass containers. Urine samples were
plated on Cystine Lactose Electrolyte-Deficient
medium (CLED), MacConkey agar and, Blood agar
(Oxoid, Basingstoke, UK) using calibrated wire
loops and then incubated aerobic atmosphere at
37oC for 24 hours. From positive cultures,
uropathogens were identified according to the
standard operational procedures as per the standard
microbiological methods14. A significant bacterium
was considered if urine culture yield < 105 colony-
forming unit (CFU/ml.
Samples from discharging ears, eye swab,
and pus from wound were collected using sterile
cotton swabs14. Specimens were inoculated onto 5%
Sheep’s blood agar, chocolate agar, mannitol salt agar
and MacConkey agar plates (Oxoid Ltd, Basing stoke
Hampshire, UK). The plates were incubated at 37oC
aerobically and examined after 24 and 48 hours.
Antimicrobial susceptibility tests
According to the standard operational procedures,
antimicrobial susceptibility tests were done on
Mueller-Hinton agar (Oxoid, Hampshire, England)
using Kirby Bauer disk diffusion method15. The
antimicrobial agents tested were: tetracycline (30 g),
nitrofurantoin (300 g), erythromycin (15 g),
chloramphenicol (30 g), gentamicin (10 g),
ciprofloxacin (5 g), cephalotin (30 μg),
cotrimoxazole (25 g), ceftriaxone (30g),
norflaxocin and amoxicillin (10g) (Oxoid,
England). Resistance data were interpreted according
to National Committee for Clinical laboratory
Standards (NCCLS)16. Reference strains of E. coli
ATCC 25922 and S. aureus ATCC 25923 were used
for quality control for antimicrobial susceptibility
The chi-square test was employed to compare the
proportion of bacterial isolates with patient sex and
age; and comparison of antimicrobial resistances. P-
value of < 0.05 was considered to indicate statistically
Ethical approval was secured from Research Ethics
Committee of Bahir Dar University. Permission
from Dessie Regional Health Research Laboratory
was also obtained.
Between 2003 and 2010, a total of 3149 samples
were analyzed for isolation and identification of
bacteria and antimicrobial susceptibility testing. E.
coli was isolated from 446 (14.2%) samples. Of these
positive cases, the isolation rate of E. coli was the
highest in urine samples 203 (45.5%), followed by
146 (32.7%) in ear discharge, 82 (18.7%) in wound
swabs and 15 (3.3%) in eye discharge (Table 1).
Table 1: Distribution of E. coli from clinical
sources at Dessie regional laboratory (2003 -
Sample Number Number % of positive
of samples positive for cases
tested E. coli
Urine 1404 203/446 45.5
Ear discharge 982 146/446 32.7
Wound swabs 677 82/446 18.7
Eye discharge 86 15/446 3.4
Total 3149 446/3149 14.2
The overall susceptibility patterns of E. coli isolates
from various clinical sources is displayed in Table 2.
Significantly high resistance rates to erythromycin
(89.4%), amoxicillin (86.0%) and tetracycline (72.6%)
were documented (p=0. 001). On the other hand,
significantly high degree of sensitivity rates to
nitrofurantoin (96.4%), norfloxacin (90.6%),
gentamicin (79.6%) and ciprofloxacin were detected
African Health Sciences Vol 11 Special Issue 1 August 2011S42
Table 2: Overall antimicrobial susceptibility patterns of E. coli isolated from clinical sources at
Dessie regional laboratory (2003 - 2010)
AntimicrobialsTotal number of Resistant
isolates tested N (%) N (%) N (%)
351 254 (72.4)
342 215 (62.9)
340 120 (35.3)
121 104 (86.0)
148 88 (59.5)
123 46 (37.4)
410 71 (13)
31 2 (6.5)
83 3 (3.6)
< 0. 001
As shown in table 3, the overall rate of multiple
drug resistance was 74.6% and only 38 (8.5 %) of
the isolates were sensitive to eight antimicrobials
tested. Site specific multiple antimicrobial resistance
rates were 100%, 76.8%, 75.7% and 67.8% for eye
discharge, urine, wound swab and ear discharge
Table 3: Multiple antimicrobial resistance patterns of E. coli isolates from clinical sources at Dessie
regional laboratory (2003 - 2010)
Antibiogram (No (%)
Source /SampleR0 R1 R2 R3 R4 R5
Urine (n=203) 15(7.4) 32(15.8) 53(16.2)
Ear (n=146)17(9.6) 30(21.9) 38(25.3) 27(17.1) 18(14.4) 9(5.5)
Total =44638(8.5) 75(16.8)
R0= Sensitive to all tested antimicrobials; R1, R2, R3, R4, R5, R6, R8 -Resistant to one, two, three, four, five,
six, eight antimicrobials, respectively.
13(2.9) 2(0.4) 1(0.2)
The chi-square test for trend shown in table 4
demonstrates increased resistance rates to seven
antimicrobials. In 2003, E. coli resistance to tetracycline
were 68.4%, to gentamicin 14.3%, chloramphenicol
50.0%, cotrimoxazole 67.2%, cephalotin 56.9%,
amoxicillin 76.9% and erythromycin 75.2%.
However, in 2010 the resistance rates were
tetracycline 76.3 %, gentamicin 13.9%,
chloramphenicol 58.1%, cotrimoxazole 68.4%,
cephalotin 91.7%, amoxicillin (93.3%) and
erythromycin 94.6%, with an increase in rates of 1.2
Table 4: Chi square test for trend applied to E. coli resistance rates to various antimicrobials for
eight years at Dessie regional laboratory (2003 - 2010)
Antimicrobials#Ta % Rb
#Ta % Rb
#Ta % Rb
Tetracycline 57 68.4 4971.4 22 77.3
Gentamicin 63 14.3 61 23.0 55 30.9
Chloramphenicol 52 50.0 50 40.0 34 44.1
Cotrimoxazole 61 67.2 55 58.2 2458.3
Cephalotine 51 56.9 32 53.1 1 100.0 3 100.0 301.6
Amoxicillin 13 76.9 32 84.4 20 90.0
Ciprofloxacin 11 36.4-
Erythromycin 4 75.04 50.0 18 88.9
#Ta % Rb
X2 for trend p- value
African Health Sciences Vol 11 Special Issue 1 August 2011
Continuation of table 4
#Ta % Rb
#Ta % Rb
56 7.8 37 21.6 36 13.9
31 21.6 37
7 31.4 8 12.5 24
100.0 2 55 2
Ciprofloxacin 358.6 43 32.6 36
Erythromycin 41 87.8 45 92.9 32 100.0
a = number of isolates tested against each antimicrobial agent
b = Percent of isolates resistant to the antimicrobial agent
#Ta % Rb
#Ta % Rb
X2 for trend p- value
Gentamicin 75 4.0
Chloramphenicol 71 16.9 50 33
Cotrimoxazole 63 71.4
Cephalotine 23 56.5
93.82 3585.776.3 43.02
37 94.668.8 <0.001
68.4 67.9 38
<0.001 50.0 30
Antimicrobial resistance in E. coli has increased
worldwide and its susceptibility patterns show
substantial geographic variation as well as differences
in population and environment17. The isolation rate
of E. coli in the present study was 14.2% and it was
commonly isolated from urine samples (45.5%).
These findings are in conformity with reports by
other researchers13, 18, 19.
In this study, the overall resistance of E. coli
to antimicrobials was high. The result is consistent
with the findings of previous studies20. The
resistance rates recorded in this study are higher than
the results of Khan et al. 6 and lower than the results
of Iqbal and Patel 21 and Okonko et al. 22. High level
of resistance in E. coli was reported to tetracycline
from a study conducted in Ethiopia23 and to
erythromycin from a study done in Slovenia24.
In all clinical samples, E. coli showed high
resistance rates of > 80% to erythromycin and
amoxicillin and > 60% to tetracycline. The results
of this study are in line with the findings of other
studies conducted in different parts of the world25,
26. However, the antimicrobial resistance rates
obtained in this study were higher compared to
susceptibility patterns reported from previous
E. coli isolates were sensitive to gentamicin,
nitrofurantoin, ciprofloxacin and chloramphenicol.
Similar studies conducted in Ethiopia30 and Nigeria31
have reported comparable susceptibility rates. High
sensitivity to ciprofloxacin and gentamicin and
norfloxacin have been recorded from previous
studies conducted in Nigeria and India31,32. In this
study, norfloxacin, ciprofloxacin, gentamicin and
chloramphenicol were found to be the most
effective antimicrobials against E. coli isolates.
Furthermore n this study, a high rate of
multiple antimicrobial resistance was recorded, which
is consistent with the reports of studies done
elsewhere21,33. The chi-square test for trend
demonstrated increased resistance rates to all
antimicrobials except ciprofloxacin. Increases in rates
of resistance to different antimicrobials have been
reported from previous studies conducted in different
parts of the world20, 33, 34.
The results of this study show high rates of
antimicrobial resistance to erythromycin, amoxicillin
and tetracycline. Nitrofurantoin, norfloxacin
gentamicin and ciprofloxacin are considered
appropriate for empirical treatment of E. coli in the
study area. Periodic monitoring of antimicrobial
susceptibility both in the community and hospital
settings is recommended.
We thank Mr Fekadu Birru, Head of Dessie Retinal
Health Research Laboratory for supporting this
research. We also thank all staff of Microbiology
department of Dessie Regional Health Research
Laboratory for their proper documentation.
1. Wagenlehner FM, Naber KG, Weidner W. Rational
antibiotic therapy of urinary tract infections. Med
Monatsschr Pharm. 2008; 31: 385-90.
2. De Francesco MA, Giuseppe R, Laura P,
Riccardo, N, Nin M. Urinary tract infections in
Brescia, Italy: Etiology of uropathogens and
African Health Sciences Vol 11 Special Issue 1 August 2011S44
antimicrobial resistance of common Uropathogens
Med Sci Moni. 2007; 13(6): 136-144.
3. Kashef N, Djavid GE, Shahbazi S. Antimicrobial
susceptibility patterns of community-acquired
uropathogens in Tehran, Iran. J Infect Dev Ctries.
2010; 4(4): 202-206.
4. Biedenbach DJ, Moet GJ, Jones RN. Occurrence
and antimicrobial resistance pattern comparisons
among bloodstream infection isolates from the
SENTRY Antimicrobial Surveillance Program
(1997–2002). Diagn Microbiol Infect Dis. 2004; 50:
5. Gebre-Sellassie S.. Antimicrobial resistance patterns
of clinical bacterial isolates in southern Ethiopia.
Ethiop Med J. 2007; 45(4): 363-370.
6. Khan NA, Saba N, Abdus S, Ali AQ. Incidence
and antibiogram patterns of E. coli isolates from
various clinical samples from patients at NIH
Islamabad. Pak J Biol Sci. 2002; (1):111-113.
7. Turner SM, Scott-Tucker A, Cooper LM,
Henderson IR. Weapons of mass destruction:
virulence factors of the global killer
enterotoxigenic Escherichia coli. FEMS Microbial
Letters. 2006; 263(1): 10-20.
8. Bell JM, Turnidge JD, Gales AC, Pfaller M. Jones
RN, Sentry APAC Study Group. Prevalence of
extended spectrum beta-lactamase (ESBL)-
producing clinical isolates in the Asia-Pacific
region and South Africa: regional results from
SENTRY Antimicrobial Surveillance Program
(1998–99). Diagn Microbiol Infect Dis. 2002; 42:
9. El Kholy A, Baseem H, Hall G, Procop GW,
Longworth DL. Antimicrobial resistance in
Cairo, Egypt 1999–2000: a survey of five
hospitals. J Antimicrob Chemother. 2003; 51: 625–
10. Dromigny JA, Nabeth P, Juergens-Behr A,
Perrier-Gros-Claude JD. Risk factors for
antibiotic resistant Escherichia coli isolated from
community-acquired urinary tract infections in
Dakar, Senegal. J Antimicrobial Chemother. 2005;
11. Erb A, Stürmer T, Marre,R BrennerH. Prevalence
of antibiotic resistance in Escherichia coli: overview
of geographical, temporal, and methodological
variations. Eur J Clin Microbial Infect Dis. 2007; 26:
12. Endalafer N, Gebre-Selassei S, Kotisso B.
Nosocomial bacterial infections in a tertiary
hospital in Ethiopia. J Infect Prev. 2011; 12 (1):
13. Yismaw G, Abay S, Asrat D, Yifru S, Kassu A
Bacteriological profile and resistant patterns of
clinical isolates from pediatric patients, Gondar
University Teaching Hospital, Gondar Northwest
Ethiopia. Ethiop. Med. J. 2010; 48(4): 293-300.
14. Cheesbourgh M. Medical laboratory manual
for tropical countries. 2nd edition: England:
Butterworth-Heineman LTD, 1991; 114-6.
15. Bauer, A.W., Kirby, W.M.M., Sherris, J.C. and
Turck, M. Antibiotic susceptibility testing by
standard single disc method. Am J. Clin Pathol
1996; 45: 493-496.
16. National Committee for Clinical Laboratory
Standards. Methods for determining bactericidal
activity of antimicrobial agents. Tentative
Guidelines, M26-TNCCLS.Villanova, PA. 1993.
17. von Baum H, Reinhard M. Antimicrobial
resistance of Escherichia coli and therapeutic
implications. Inter J Med Microbiol. 2000; 295: 503–
18. Al-Tawfiq JA. Increasing antibiotic resistance
among isolates of Escherichia coli recovered from
inpatients and outpatients in a Saudi Arabian
Hospital. Infect Control Hosp Epidemiol 2006; 27:
19.Gangoué JP, Koulla-Shirob S, Ngassama P,
Adiogo D, Njine T, Ndumbe P. Antimicrobial
resistance of Gram-negative bacilli isolates from
inpatients and outpatients at Yaounde Central
Hospital, Cameroon. Inter J Infect Dis. 2004; 8:
20. Orrett FA, Shurl SM. Prevalence of resistance to
antimicrobial of E. coli isolates from clinical
sources at a private hospital in Trinidad. Jpn J
Infect Dis. 2001; 54: 64-68.
21. Iqbal MK, Patel IK. Susceptibility patterns of
Escherichia coli: Prevalence of multidrug-resistant
isolates and extended spectrum beta-Lactamase
phenotype. J Pak Med Asso. 2002; 52: 407-417.
22.Okonko IO. Soleye FA, Amusan TA, Ogun
AA, Ogunnusi TA Ejembi J. Incidence of
multi-drug resistance (MDR) organisms in
Abeokuta, Southwestern Nigeria. Global J Pharm.
2009; 3(2): 69-80.
African Health Sciences Vol 11 Special Issue 1 August 2011 Download full-text
23.Andargachew M, Feleke M, Tesesma B, Afewerk
K. Pattern and multiple drug resistance of
bacterial pathogens isolated from wound
infection at University of Gondar Teaching
Hospital, Northwest Ethiopia. Ethiop Med J. 2006;
24. Petkovs¡ek Z, Elers¡ic¡ K, Gubina M, Z¡gur-
Bertok D, Erjavec S. Virulence potential of
Escherichia coli isolates from skin and soft tissue
infections. J Clin Microbiol. 2009; 47(6): 1811–
25. Bharathi MJ, Ramakrishnan R, Maneksha V,
Shivakuma C, Mittal S. Comparative
bacteriology of acute and chronic dacryocystitis.
Eye 2008; 22: 953–960.
26. Briscoe D, Rubowitz A, Assia EI. Changing
bacterial isolates and antibiotic sensitivities of
purulent dacryocystitis. Orbit 2005; 24: 95–98.
27. Zhanel, GG, Hisanaga TL, Laing NM, De Corby
MR, Nichol KA, Weshnoweski et al. Antibiotic
resistance in Escherichia coli outpatient urinary
isolates: final results from the North American
Urinary Tract Infection Collaborative Alliance
(NAUTICA). Int J Antimicrob Agents. 2006; 27:
28. Karlowsky JA, Kelly LJ, Thornsberry C, Jones
ME Sahm DF. Trends in antimicrobial resistance
among urinary tract infection isolates of Escherichia
coli from female outpatients in the United States.
Antimicrob Agents Chemother. 2002; 6: 2540–2545.
29. Barrett SP, Savage MA, Rebec MP, Guyot A,
Andrews N, Shrimpton SB. Antibiotic sensitivity
of bacteria associated with community-acquired
urinary tract infection in Britain. J Antimicrob
Chemother. 2000; 44: 359–365.
30.Tesfaye G, Asrat D, Woldeamanuel Y, Gizaw M.
Microbiology of discharging ears in Ethiopia.
Asian Pac J Trop Med 2009; 2(91): 60-67.
31. Wariso BA,Ibe SN. Bacteriology of chronic
discharging ears in Port Harcourt, Nigeria. West
Afr J Med. 2006; 25: 219-222.
32. Bharathi MJ, Ramakrishnan R, Meenakshi R,
Palaniappan R. In-Vitro efficacy of antibacterials
against bacterial isolates from corneal ulcers.
Indian J Ophthalmol. 2002; 50: 109–114.
33. Kurutepe S, Surucuoglue S, Sezgin C, Gazi H,
Gulay M, Ozbakkaloglu B. Increasing
antimicrobial resistance in E.coli isolates form
community-acquired urinary tract infections
during 1998 – 2003 in Minisa, Turkey. Jpn J Infect
Dis. 2005; 58: 159-161.
34. Kahlmeter G. An international survey of the
antimicrobial susceptibility of pathogens from
uncomplicated urinary tract infections: the ECO-
SENS Project. J Antimicrobl Chemother. 2003; 51: