Contamination levels and transferability of antimicrobial resistance by Escherichia coli isolated from raw retail chicken meats in Nairobi, Kenya.

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, low-middle 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). 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.