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Antimicrobial Resistance in Salmonella and Escherichia coli Isolated from Commercial Shell Eggs

M. T. Musgrove^*,1, D. R. Jones^*, J. K. Northcutt, N. A. Cox, M. A. Harrison, P. J. Fedorka-Cray^|| and S. R. Ladely^||

^* Egg Safety and Quality Research Unit, Poultry Processing Research Unit, Poultry Microbiological Safety Research Unit, and ^|| Bacteriology, Epidemiology, and Antimicrobial Resistance Research Unit, United States Department of Agriculture, Agricultural Research Service, Athens, GA 30604; and Department of Food Safety and Technology, University of Georgia, Athens 30602

¹ Corresponding author: mmusgrov{at}saa.ars.usda.gov

The development of antimicrobial resistance in bacteria has become a global problem. Isolates of Salmonella and Escherichia coli recovered from shell egg samples, collected at 3 commercial plants, were analyzed for resistance to 16 antimicrobial agents (n = 990). Eggs were sampled by rinsing in a saline solution. Pooled samples were preenriched in buffered peptone water and then selectively isolated using standard broths and agars. Salmonella-positive isolates were serogrouped immunologically before being serotyped. Enterobacteriaceae were enumerated from individual samples using violet red bile glucose agar plates. Escherichia coli were identified biochemically from presumptive Enterobacteriaceae isolates. Salmonella and generic E. coli antimicrobial-susceptibility testing was conducted using a semiautomated broth microdilution system. More resistance was observed in the Salmonella isolates (n = 41) than in the E. coli isolates (n = 194). Salmonella Typhimurium was the most prevalent (69.0%) serotype and demonstrated the greatest multiple resistance. Salmonella Kentucky, the least prevalent (5.0%) serotype recovered, was the most susceptible. Although 34.1% of the Salmonella serotypes were susceptible to all antimicrobial agents, 60.1% were resistant to 11 or more compounds. Many Salmonella isolates exhibited resistance to tetracycline (63.4%), nalidixic acid (63.4%), and streptomycin (61.0%). Most E. coli isolates (73.2%) were susceptible to all antimicrobial drugs. Many E. coli isolates exhibited resistance to tetracycline (29.9%), streptomycin (6.2%), and gentamicin (3.1%). Only 1% of the E. coli isolates were resistant to 4 antimicrobial agents. These data indicate that shell eggs can harbor resistant foodborne and commensal bacteria; among Salmonella isolates, resistance was serotype-dependent.

Key Words: Salmonella • Escherichia coli • egg • antimicrobial resistance

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				M. T. Musgrove, J. K. Northcutt, D. R. Jones, N. A. Cox, and M. A. Harrison Enterobacteriaceae and Related Organisms Isolated from Shell Eggs Collected During Commercial Processing Poult. Sci., June 1, 2008; 87(6): 1211 - 1218. [Abstract] [Full Text] [PDF]