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Appl. Environ. Microbiol. doi:10.1128/AEM.01444-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Influx of enterococci and associated antibiotic resistance and virulence genes from ready-to-eat food to the human digestive tract

Department of Diagnostic Medicine and Pathobiology, Department of Entomology, Kansas State University, Manhattan, KS 66506

^* To whom correspondence should be addressed. Email: lzurek{at}ksu.edu.

	Abstract

The influx of enterococcal antibiotic resistance (AR) and virulence genes from ready-to-eat-food (RTEF) to the human digestive tract was assessed. Three RTEFs (chicken salad, chicken burger, carrot cake) were sampled from five fast-food restaurants five-times in summer and winter. The prevalence of enterococci was significantly higher in summer (92.0% salad and 64.0% burger) than in winter (64.0% salad and 24.0% burger). The overall concentration of enterococci during both seasons was similar (10³ CFU/g); the most prevalent were Enterococcus casseliflavus (41.5% of isolates) and E. hirae (41.5%) in winter (WI), and E. faecium (36.8%), E. casseliflavus (27.6%), and E. faecalis (22.4%) in summer (SU). Resistance in WI was detected primarily to tetracycline (50.8%), ciprofloxacin (13.8%), and erythromycin (4.6%). Summer isolates were mainly resistant to tetracycline (22.8%), erythromycin (22.1%), and kanamycin (13.0%). The most common tet-gene was tet(M) (35.4% WI, 11.9% SU). The prevalence of virulence genes (gelE, asa1, cylA, esp) and marker genes for clinical isolates (ef0573, ef0592, ef0605b, paief0050, ef1420b, ef2144) was low (12.3%). Genotyping of E. faecalis and E. faecium using pulsed-field gel electrophoresis revealed that the food contamination likely originated from various sources and it was not clonal. Our conservative estimate (single AR gene copy per cell) for the influx of tet-genes alone to the human digestive tract is 3.8 x 10⁵ per meal (chicken salad). This AR gene influx is frequent because RTEF are commonly consumed and that may play a role in the acquisition of AR determinants in the human digestive tract.