Prevalence and Antimicrobial Resistance of Enterobacteriaceae in Shell Eggs from Small-Scale Poultry Farms and Farmers' Markets

Abstract

Public health concerns over the emergence of antimicrobial resistant bacteria have increased recently. The purpose of this study was to investigate the prevalence of antimicrobial resistant Enterobacteriaceae in shell eggs purchased from small poultry farms and farmers' markets. A total of 504 eggs were pooled to make 252 composite samples, consisting of 2 eggs per composite. The microbial quality of shell eggs was determined by standard quantitative, biochemical, and PCR techniques. Susceptibility to 13 antimicrobial agents was determined by the Kirby-Bauer disk diffusion technique, and results were interpreted based on Clinical and Laboratory Standards Institute values. Shell eggs and egg contents were positive for Escherichia coli (11.9 and 5.2%, respectively), Enterobacter (9.1 and 7.9%), and Serratia (11.5 and 4.8%). Salmonella was isolated from 3.6% of egg shells but not from egg contents. Mean (±SD) Enterobacteriaceae levels (4.4 ± 2.0 log CFU per eggshell) on shell eggs from poultry farms was significantly higher (P ≤ 0.05) than that on shell eggs from farmers' markets (2.1 ± 1.3 log CFU per eggshell). Of the 134 isolates recovered, resistance among isolates from farm and market shell eggs to erythromycin was most common (48.5 and 32.8%, respectively) followed by ampicillin (44.8 and 17.2%), and tetracycline (29.9 and 17.2%). The multiple antibiotic resistance index value for E. coli and Pantoea was 0.62, and that for Salmonella and Klebsiella terrigena was 0.08, indicating that Enterobacteriaceae in shell eggs can be resistant to multiple antimicrobial agents. These data reveal that shell eggs from small poultry farms and farmers' markets can harbor antimicrobial resistant pathogenic and commensal bacteria. Thus, failure to properly handle shell eggs poses a potential health hazard to consumers.