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: International Association for Food Protection
Publication Type: Abstract Only
Publication Acceptance Date: 4/17/2005
Publication Date: 9/13/2005
Citation: Musgrove, M.T., Jones, D.R., Northcutt, J.K., Cox Jr, N.A., Harrison, M.A., Cray, P.J., Ladely, S.R. 2005. Antimicrobial resistance in salmonella and escherichia coli isolated from commercial shell eggs [abstract]. Paper No. T2-12.

Interpretive Summary:

Technical Abstract: Development of bacterial resistance to antimicrobials commonly used in agriculture and human medicine has been increasingly observed in recent years. Isolates of Salmonella and Escherichia coli recovered from shell egg samples were analyzed for resistance to 16 antimicrobials. Shell eggs (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. After being sero-grouped, confirmed isolates were sero-typed by the National Veterinary Services Laboratory. Enterobacteriaceae were enumerated from individual shell rinse samples using violet red bile glucose agar plates. E. coli were obtained by biochemical identification of randomly selected presumptive Enterobacteriaceae isolates. Salmonella and generic E. coli antimicrobial susceptibility testing was conducted using an automated micro-broth dilution system. Antimicrobial compounds included those used in human and veterinary medicine and were configured in a 96 well custom-made panel. National Committee for Clinical Standards guidelines were followed throughout the testing procedure. More resistance was observed in the 41 Salmonella isolates that were tested than in the 194 E. coli isolates. S. Typhimurium was the most prevalent (69.0%) serotype and demonstrated the greatest resistance to the antimicrobial compounds tested. S. 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.