ANTIMICROBIAL RESISTANCE IN SALMONELLA AND ESCHERICHIA COLI ISOLATED FROM COMMERCIAL SHELL EGGS

Authors: Musgrove, Michael; Jones, Deana; Northcutt, Julie; Cox Jr, Nelson; HARRISON, M - UGA; Cray, Paula; Ladely, Scott

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2006
Publication Date: 9/1/2006
Citation: Musgrove, M.T., Jones, D.R., Northcutt, J.K., Cox Jr, N.A., Harrison, M.A., Cray, P.J., Ladely, S.R. 2006. Antimicrobial resistance in salmonella and escherichia coli isolated from commercial shell eggs. Poultry Science. 85:1665-1669.

Interpretive Summary: Bacterial antimicrobial resistance is a world-wide concern. Resistance to antimicrobials used in humans and veterinary medicine has been documented in bacteria collected from many foods and environmental sources. .However, few studies have reported on antimicrobial resistance in bacteria isolated from shell eggs. In this study, Salmonella and Escherichia coli which had been isolated from shell eggs collected at three commercial processing plants were screened for resistance to 16 antimicrobials. 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 also the most susceptible. While 34.1 % of the Salmonella were susceptible to all compounds, 60.1 % were resistant to more than 5 compounds. Antimicrobials for which the greatest numbers of Salmonella isolates exhibited resistance were Tetracycline (63.4%), Nalidixic acid (63.4%), and Streptomycin (61.0%). A majority of the E. coli isolates (73.2%) were susceptible to all compounds studied. Compounds for which the greatest numbers of E. coli isolates exhibited resistance were Tetracycline (29.9%), Streptomycin (6.2%), and Gentamicin (3.1%). Only 1% of the E. coli isolates were resistant to 4 compounds. This information will be used by national antimicrobial resistance monitoring systems and by risk analysis experts. These data indicate that shell eggs can harbor resistant food-borne and commensal bacteria. However, among Salmonella isolates, resistance was serotype dependent.

Technical Abstract: Development of antimicrobial resistance in food-borne and commensal bacteria has become a global problem. Isolates of Salmonella and Escherichia coli recovered from shell egg samples were analyzed for resistance to 16 antimicrobials. Shell eggs (n = 990) were obtained from 3 commercial plants at 12 points along the processing chain. Eggs were individually sampled by rinsing in a saline solution. Pooled samples were pre-enriched in buffered peptone water and selectively enriched in TT and Rappaport-Vassiliadis broths. Presumptive Salmonella colonies from selective agar plates (BGS and XLT-4) were inoculated onto lysine iron and triple sugar iron agar slants. Salmonella positive isolates were sero-grouped using a slide agglutination technique before being sero-typed by the National Veterinary Services Laboratories. Enterobacteriaceae were enumerated from individual shell rinse samples using Violet Red Bile Glucose agar plates. Escherichia coli were obtained by biochemical characterization of randomly selected presumptive Enterobacteriaceae isolates. Salmonella and generic E. coli antimicrobial susceptibility testing was conducted using a semi-automated broth micro-dilution system. Antimicrobial compounds included those used in human and veterinary medicine and were configured in a 96 well custom-made panel. Clinical and Laboratory Standards Institute guidelines were followed throughout the testing procedure. 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 also the most susceptible. While 34.1 % of the Salmonella were susceptible to all compounds, 60.1 % were resistant to 11 or more compounds. Antimicrobials for which the greatest numbers of Salmonella isolates exhibited resistance were Tetracycline (63.4%), Nalidixic acid (63.4%), and Streptomycin (61.0%). A majority of the E. coli isolates (73.2%) were susceptible to all compounds examined. Compounds for which the greatest numbers of E. coli isolates exhibited resistance were Tetracycline (29.9%), Streptomycin (6.2%), and Gentamicin (3.1%). Only 1% of the E. coli isolates were resistant to 4 compounds. These data indicate that shell eggs can harbor resistant food-borne and commensal bacteria. However, among Salmonella isolates, resistance was serotype dependent.