Genetic Diversity and Antimicrobial Resistance of Escherichia coli from Human and Animal Sources Uncovers Multiple Resistances from Human Sources

A Mark Ibekwe,Shelton E Murinda,Alexandria K Graves,Dee A Carter

doi:10.1371/journal.pone.0020819

Abstract

Escherichia coli are widely used as indicators of fecal contamination, and in some cases to identify host sources of fecal contamination in surface water. Prevalence, genetic diversity and antimicrobial susceptibility were determined for 600 generic E. coli isolates obtained from surface water and sediment from creeks and channels along the middle Santa Ana River (MSAR) watershed of southern California, USA, after a 12 month study. Evaluation of E. coli populations along the creeks and channels showed that E. coli were more prevalent in sediment compared to surface water. E. coli populations were not significantly different (P = 0.05) between urban runoff sources and agricultural sources, however, E. coli genotypes determined by pulsed-field gel electrophoresis (PFGE) were less diverse in the agricultural sources than in urban runoff sources. PFGE also showed that E. coli populations in surface water were more diverse than in the sediment, suggesting isolates in sediment may be dominated by clonal populations.Twenty four percent (144 isolates) of the 600 isolates exhibited resistance to more than one antimicrobial agent. Most multiple resistances were associated with inputs from urban runoff and involved the antimicrobials rifampicin, tetracycline, and erythromycin. The occurrence of a greater number of E. coli with multiple antibiotic resistances from urban runoff sources than agricultural sources in this watershed provides useful evidence in planning strategies for water quality management and public health protection.

Highlights

E. coli are widely used as indicators of fecal contamination of waterways in most urban areas
Concentrations of E. coli were significantly lower (P = 0.05) at this site compared to the other sites that were impacted by agricultural activities and urban runoff, and site ST5, which is the influent water to Prado Park/wetland/dam (Fig. 2)
Prevalence of E. coli in the watershed In this study, the concentration of E. coli in the two major creeks and the Prado area exceeded the single sample objectives for E. coli: 235 CFU/100 mL, according to the United States Environmental Protection Agency (USEPA) that is used in many parts of the country for National Pollutant Discharge Elimination System and Total Maximum Daily Load purposes [24]

Summary

Introduction

E. coli are widely used as indicators of fecal contamination of waterways in most urban areas. In a typical mixed watershed, host sources of E. coli may be from humans, farm animals, wildlife, and pets, among others [2,3] These hosts are generally described as primary habitats, and until recently E. coli was believed to survive poorly in the environment, and not to grow in secondary habitats such as surface water, sediment, and soil [4,5]. The level of selective pressure exerted in a mixed catchment area may be a useful criterion for identifying the host sources of E. coli in the watershed. One such tool to aid with examining the selection pressure on E. coli is assessing their antimicrobial sensitivities [12,13]. In 2003, the FDA directly addressed the issue of risks associated with use of antibiotics in food animals with the release of the Guidance for Industry 152 (www.fda.gov/cvm), which outlined steps for risk assessment in the evaluation of new animal drugs in terms of microbial food safety [16]

Methods

Results

Conclusion