Abstract:
Chicken is a rich source of meat protein and is increasingly being consumed in urban
Kenya. However, under poor hygienic conditions, raw chicken meat can be an efficient
medium for the spread of infectious agents including bacteria such as Escherichia coli
and other coliforms which indicate the potential presence of other pathogenic bacteria.
In addition, bacterial contaminants in the meat may contain antimicrobial resistance
genes that can be transferred to other bacteria and to the human population resulting in
food borne infections with multidrug resistant pathogens. This study assessed the
microbiological quality and safety of consumption of raw retail chicken meats sold in
Nairobi, Kenya. Focus was laid on determining the E. coli/Coliform contamination
levels, the antimicrobial resistance profiles and virulence of the E. coli isolates. A cross
sectional study design was used. Sample collection was done from August 2011 to
February 2012. Two hundred raw chicken meat samples were randomly purchased from
across five different classes of meat outlets around Nairobi city, namely; high income
area butcheries, high-middle income area butcheries, low income area butcheries, lowmiddle income area butcheries and supermarkets. Enumeration of E. coli and coliform
bacteria was done using 3M petrifilm E. coli/Coliform count plates. Isolation and
identification of E. coli was done by standard cultural and biochemical testing. Isolated
E. coli were subjected to antimicrobial susceptibility testing using 12 commonly
prescribed antimicrobials by means of Kirby Bauer disc diffusion method. Susceptibility
data was interpreted according to criteria set by the Clinical and Laboratory Standards
Institute (2012). Polymerase chain reaction assays were used to determine presence of
virulence genes in the isolated E. coli. Isolates resistant to 3 or more antibiotics were
subjected to in-vitro conjugation and plasmid DNA content analysis to test for
transferability of resistance genes. Graphs and tables were used for data presentation and
statistical tests were done by means of Statistical Package for Social Sciences (SPSS).
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The overall E. coli contamination rate was 78% while coliform contamination rate was
97%. The average E. coli and coliform counts for all samples were above the acceptable
microbial count limit (>100 cfu/ml). There was a significant difference in the E.
coli/coliform counts (p< 0.001) among the 5 classifications of retail outlets. Samples
from supermarkets had lower E. coli and coliform counts compared to the rest. Seventy
five per cent of the isolates exhibited resistance to at least one of the 12 antibiotics
tested. Resistance to tetracycline was the highest at 60.3%. E. coli isolates that tested
positive for the presence of at least one of 10 virulence genes tested were 40.4 %. Fifty
five percent of the isolates successfully transferred resistance by conjugation and
together with 17 trans-conjugants, all contained plasmids of molecular weights varying
between 3.0-53.7Kb. In conclusion, our data showed high levels of contamination in raw
retail chicken meat by E. coli and other coliform bacteria in various retail outlets in
Nairobi, Kenya. Raw chicken meat was observed to carry virulent strains of E. coli with
ability to transfer their resistance via conjugation to other bacteria. Prevalence of
antimicrobial resistance among the E. coli isolates was considerably high especially for
commonly available antimicrobials such as tetracycline. These data will be useful for
risk assessment and risk management for implementation of an effective food safety
management system in Nairobi, Kenya