Enterococcus in surface waters from the Des Moines River (Iowa) watershed: location, persistence and vancomycin resistance

Abstract

The object of this study was to quantify vancomycin-resistant enterococci in surface water from Central Iowa obtained from April 2007 to August 2007. Water from established sampling sites in four watersheds was plated on bile-esculin agar. Presumptively identified enterococci were categorized as “above the level of concern” if the sample contained ≥107 CFU per 100 ml. Confirmation of isolates as enterococci was based on growth at elevated temperature in high salt and on Enterococcus agar. Isolates that grew on 6 μg/ml vancomycin agar were deemed resistant. PCR analysis of resistant strains characterized vancomycin resistance genes. 77.2% of surface water samples from Central Iowa contained enterococci. Among enterococcal isolates, 10.4% grew on media containing 6 μg/ml vancomycin. PCR analysis of resistance genes showed a preponderance of VanC2/C3 in the area studied and VanB was not detected. Vancomycin-resistant Enterococcus is present in Central Iowa surface waters but resistance rarely involved VanA genotypes. Nevertheless, the potential for community-acquired infections remains a risk.

Keywords:

• water quality
• Enterococcus
• vancomycin resistance

Acknowledgements

The following summer research students assisted with the laboratory analysis of water samples reported in this paper. Michelle Evans, undergraduate student at Heidelberg College, Tiffin, Ohio, USA; Anshul Dutta, undergraduate student at Drake University, Des Moines, Iowa USA and Dante Samuel, medical student at Des Moines University, Des Moines, Iowa, USA.