Bacterial occurrence in kitchen hand towels

Abstract

The common occurrence of enteric bacteria in kitchen sponges and dishcloths suggests that they can play a role in the cross-contamination of foods, fomites and hands by foodborne pathogens. This study investigated the occurrence of bacteria in kitchen towels often used to dry dishes, hands and other surfaces in the domestic kitchen. A total of 82 kitchen hand towels were collected from households in five major cities in the United States and Canada and the numbers of heterotrophic bacteria, coliform bacteria, and Escherichia coli in each towel were determined. In addition, identification of the enteric bacteria was performed on selected towels. Coliform bacteria were detected in 89.0% and E. coli in 25.6% of towels. The presence of E. coli was related to the frequency of washing.

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*Corresponding author: Phone: +1 520.621.6906; Fax: +1 520.621.6366; E-mail: gerba@ag.arizona.edu
ABSTRACT
The common occurrence of enteric bacteria in kitchen
sponges and dishcloths suggests that they can play a
role in the cross-contamination of foods, fomites and
hands by foodborne pathogens. This study investigated
the occurrence of bacteria in kitchen towels often used
to dry dishes, hands and other surfaces in the domestic
kitchen. A total of 82 kitchen hand towels were collected
from households in five major cities in the United States
and Canada and the numbers of heterotrophic bacteria,
coliform bacteria, and Escherichia coli in each towel
were determined. In addition, identification of the enteric
bacteria was performed on selected towels. Coliform
bacteria were detected in 89.0% and E. coli in 25.6%
of towels. The presence of E. coli was related to the
frequency of washing.
INTRODUCTION
Several studies have documented the common occurrence
of large populations of heterotrophic and enteric bacteria in
kitchen sponges and dishcloths (1, 2, 5, 8), where the moist
environment and collected food residues create an ideal
environment for the growth of bacteria. Enriquez et al. (2)
found total and fecal coliform bacteria in large numbers in
cellulose sponges and dishcloths, sometimes reaching levels
greater than 106 colony-forming-units (CFU) per ml in uid
squeezed from these cleaning tools. Salmonella spp. was
isolated from almost 14% of the dishcloths. Sco et al. (8)
documented the occurrence of E. coli in kitchen towels, and
Maick et al. (4) reported isolation of Camplyobacter from
tea towels in the kitchen aer preparation of meals made
with poultry. Sco and Bloomeld (6) documented the
survival of Salmonella and E. coli in coon kitchen cloths and
suggested they may play a role in cross-contamination in the
home environment. e goal of this study was to assess the
occurrence of total and enteric bacteria in kitchen towels as it
relates to environmental and towel cleaning.
1Dept. of Soil, Water and Environmental Science,
University of Arizona, Tucson, AZ 85721, USA
2Kimberly-Clark Corporation, 2100 Winchester Road,
Neenah, WI 54956, USA
Charles P. Gerba,1* Akrum H.
Tamimi,1 Sherri Maxwell,1 Laura Y.
Sifuentes,1 Douglas R. Hoffman2
and David W. Koenig2
PEER-REVIEWED ARTICLE
Food Protection Trends, Vol 34, No. 5, p.312-317
Copyright©2014, International Association for Food Protection
6200 Aurora Ave., Suite 200W, Des Moines, IA 50322-2864
Bacterial
Occurrence in
Kitchen Hand
Towels

foodprotection.org Food Protection Trends 313
MATERIAL AND METHODS
e study was conducted in ve major cities in North
America: Chicago, IL; Tucson, AZ; New Orleans, LA;
Orlando, FL and Toronto, ON, Canada. e numbers of
towels collected from each city is presented in Table 1. ese
cities represent dierent weather conditions, varying from
cold to hot and from dry to humid.
Random households were selected in each city and towels
were collected by going door to door and requesting one
used towel from the kitchen. A survey of household towel
use and characteristics also was conducted for each house
selected. e information was obtained from the person in
the household who provided the towel. A total of 82 kitchen
towels were collected.
e questions in the survey were related to towel use and
frequency of cleaning. ese questions identied: age of
towel in months, frequency of washing of towel in days per
month, towel frequency of use, and the number of days since
the towel was last washed.
Each collected and used kitchen towel was submerged
in peptone broth (Difco, Sparks, MD) to extract bacteria
from the towel. Each towel was placed in a stomacher bag
with either 500 or 250 ml of peptone broth, based on towel
size and the material’s absorbance, to guarantee full soaking
of the towel. Each towel was then manually kneaded in the
peptone broth (Difco, Sparks, MD) for ve minutes until
the broth was completely absorbed by the towel. e broth
was extracted from the towel by wringing the liquid out by
pressing it against two stainless steel metal plates (AK Steel,
Cincinnati, OH). e extract or dilution (10-fold dilutions in
peptone broth) was plated on selective media for isolation of
the various bacterial populations.
Each towel was tested for total bacteria (heterotrophic
bacteria counts; HPC), coliform bacteria, and Escherichia
coli. HPC were assayed by spread plating on R2A media
(Difco, Sparks, MD) or aer dilution (in phosphate buered
saline). Aer incubation for 5 days at 25°C, viable colonies
were counted. Coliforms and E. coli were assayed by the most
probable number (MPN) method, using the Colilert Quanti-
tray method (IDEXX; Westbrook, ME), and enumerated
aer incubation at 35°C for 24 hours. A maximum of 100
ml of the towel extract could be assayed by this method.
Selected coliforms and presumptive E. coli isolates from
randomly selected towels were picked from petri plates and
identied by use of API bacterial identication test kits 20E
(bioMérieux, Marcy-l’Etoile, France).
e average area of the kitchen towels, for all cities, was
calculated to be about 1000 cm2, with a standard deviation of
150 cm2. erefore, it was decided to do all analyses on a per
towel basis.
A database was developed, and all collected data from the
survey and the laboratory analytical data were entered in the
database (see Tables 1 through 3). Data were manipulated in
various manners and multiple analyses of variance (ANOVA)
were conducted on the data to assess relationships between
demographics and characteristics of the towels and their use.
Microso Excel was used for the analysis (Microso Corp.,
Redmond, WA). A completely randomized design was used
to perform the ANOVA, with a rejection region of 5% using
the F distribution.
RESULTS
e results for overall occurrence of the studied bacteria
are presented as both arithmetic and geometric averages
TABLE 1. Average arithmetic mean of bacterial populations found on kitchen hand towels
(CFU or MPN) collected from various cities
City HPC* Coliforms E. coli
Mean St. Dev n Mean St. Dev n Mean St. Dev n
Chicago 2.98E + 08 6.12E + 08 19 4.76E + 03 1.10E + 04 20 6.00E + 00 1.92E + 01 20
Tucson 1.62E + 08 2.31E + 08 19 2.55E + 06 1.11E + 07 20 1.51E + 03 6.73E + 03 20
New Orleans 9.42E + 08 1.19E + 09 4 5.50E + 03 4.02E + 03 4 1.05E + 01 1.33E + 01 4
Orlando 8.30E + 07 1.38E + 08 18 3.97E + 05 8.64E + 05 19 7.24E + 03 1.68E + 04 19
Toronto 9.49E + 07 2.22E + 08 19 1.04E + 04 2.24E + 04 19 1.34E + 00 4.80E + 01 19
Average/Total 3.16E + 08  79 5.93E + 05  82 1.75E + 03  82
*HPC: Heterotrophic Plate Count

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314
(Tables 1 and 2). Figure 1 shows that all kitchen towels for
the 5 cities had at least 1 × 103 CFU/towel, and some had
HPC greater than 1 × 109 CFU/towel. e overall average
was 3.16 × 108 CFU/towel. At least one MPN of coliform
bacteria was found on towels collected from most cities, and
values higher than 1 × 106 MPN were observed in two cities
(Tucson and Orlando).
E. coli concentrations on kitchen towels were about one
MPN per towel, but values as high as 1 × 104 CFU/towel were
observed in some cities. Coliform bacteria were detected in
almost all of the towels (89.0%) and E. coli in 25.6%.
e highest numbers of bacteria per towel were found in
those collected from New Orleans and the lowest in towels
collected from Orlando (Table 1 and Fig. 1). Tucson had the
TABLE 2. Average geometric means of bacteria found in kitchen towels
(log10 CFU or MPN/towel) collected from various cities
City HPC* Coliforms E. coli
Geo. Mean St. Dev n Geo. Mean St. Dev n Geo. Mean St. Dev n
Chicago 6.8 1.9 20 2.0 1.4 20 0.3 0.4 20
Tucson 7.6 1.3 20 3.4 1.8 20 0.4 1.0 20
New Orleans 8.3 1.1 4 3.7 0.3 4 0.7 0.7 4
Orlando 7.3 1.4 19 3.9 2.1 19 1.6 1.7 19
Toronto 6.1 1.7 19 2.8 1.4 19 1.3 0.5 19
Average/Total 7.2  82 3.2  82 0.9  82
*HPC: Heterotrophic Plate Count
TABLE 3. Statistical differences between parameters studied for kitchen towels collected
in the study
Parameter HPC* Coliforms E. coli
Between cities <0.009 <0.006 <0.0003
Age of towel
(<12 or >12 months) 0.446 0.481 0.424
Frequency of washing
(<3 or >4 days) 0.675 0.351 0.014
Frequency of use
(<7 times a day or >8) 0.012 0.981 0.780
Last time washed
(1 day vs. >2) 0.066 0.321 0.172
*HPC: Heterotrophic Plate Count
Note: Bold and underlined values indicate signicant dierences (P < 0.05).

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FIGURE 1. Distribution of heterotrophic plate counts (HPC) found in kitchen towels
collected om various cities; each value represents an individual towel.
Sample ID
HPC (MPN/Towel)
1.0E+10
1.0E+09
1.0E+08
1.0E+07
1.0E+06
1.0E+05
1.0E+04
1.0E+03
0 5 10 15 20
FIGURE 2. Distribution of coliform bacteria numbers found on kitchen towels collected om
various cities; each value represents an individual towel.
Sample ID
Coliforms (MPN/Towel)
1.0E+08
1.0E+07
1.0E+06
1.0E+05
1.0E+04
1.0E+03
1.0E+02
1.0E+01
1.0E+00
0 5 10 15 20

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FIGURE 3. Distribution of E. coli found on kitchen towels collected om ve of the cities studied;
each value represents an individual towel.
Sample ID
E.coli (MPN/Towel)
1.0E+05
1.0E+04
1.0E+03
1.0E+02
1.0E+01
1.0E+00
1.0E-01
0 5 10 15 20
highest numbers of coliform bacteria in the towels, followed
by number of E. coli isolated from towels collected in Orlando
(Table 1 and Figures 2 and 3).
Because the distribution of the bacteria exhibited a log
normal distribution, it was log transformed for further
analysis (Table 2). ere was a statistically signicant
relationship between city of collection and all types of
bacteria isolated. Frequency of use was related to the
numbers of HPC, while the concentration of E. coli was
related to the frequency of washing. In addition to E. coli,
other bacteria identied in the towels included Enterobacter
cloacae, Klebsiella pneumonia and K. oxytoca.
DISCUSSION
is is the rst study to address the concentrations and
types of enteric bacteria in kitchen hand towels. Sco et al.
(8) studied the occurrence of bacteria in kitchen towels in
the United Kingdom but sampled the surfaces only by use of
Rodac plates. In that study, E. coli was detected in 1.9% and
coliforms in at least 4.1% of the kitchen towels. e genera
of bacteria detected in their study were similar to the ones
observed in the present study. We detected coliforms in
89.0% and E. coli in 25.6% of the towels. e greater numbers
we observed are most likely because we extracted the bacteria
from the towel using an eluent to obtain a total count of the
bacteria on and within the towel.
e relationship between the numbers of bacteria and
the dierent cities (excluding New Orleans, since it had so
few samples) was statistically signicant, which may reect
climate and dierent use paerns or types of food prepared.
Statistically signicant lower numbers of HPC occurred in
towels that were washed less (Table 3). E. coli numbers also
were related to the frequency of washing, with numbers on
towels being lower the more oen they were washed. Age of
the towel and days since last time washed did not inuence
the concentration of any of the bacteria in the towels. e
results suggest that E. coli is particularly easily removed
during washing or requires an unusually long time to colonize
and grow in the towels. Coliforms, E. coli and Salmonella can
survive the drying of kitchen cleaning cloths and regrow if
the cloth becomes soiled again (3).
Maick et al. (4) also reported the isolation of Camplyo-
bacter from a kitchen towel of a domestic kitchen aer prepa-
ration of chicken naturally contaminated with the organism.
e researchers aributed the isolation of this pathogen
to poor hand washing, followed by wiping of the dirty
hands aer handling the chicken. e same group reported
cross contamination of dishes when wiped dry with towels
contaminated with E. coli O157:H7, Salmonella or Campy-
lobacter jejuni (4). e researchers recommended frequent
replacement or decontamination of kitchen towels. Sco and
Bloomeld (7) reported that detergent washing and drying of
kitchen cloths in the kitchen only slightly reduced microbial

foodprotection.org Food Protection Trends 317
contamination, and regrowth occurred within 24 hours, since
the towels remained damp. e researchers demonstrated
that soaking the cloths in 4,000 mg/L of bleach for two
minutes was more eective in reducing bacterial numbers;
however, not all the cloths could be decontaminated,
probably because of dierences in organic load.
is current study demonstrated that signicant numbers
of coliform and E. coli commonly occur in kitchen towels.
ese results also demonstrate the potential for cross-
contamination of foodborne enteric bacterial pathogens
and their growth in kitchen towels.
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