Comparison of the Diversity of E. coli Isolates Obtained from Surface Water Samples Using Different Enumeration Methods.

Standard methods for water testing utilize varying techniques for both the cultivation and enumeration of E.coli as an indicator of fecal contamination.  Traditional most probable number assays as well as membrane filtration methods have been compared based on their ability to enumerate E.coli for water quality assessment.  E. coli, for library-dependent microbial source tracking (MST) efforts, are typically constructed from known fecal sources using one or a combination of these enumeration methods.  However, if different enumeration methods select for different E. coli populations, this could bias and/or confound MST results.  To our knowledge, no evaluation of E.coli community compositional effects of these accepted methods has been conducted.  The objective of this study was to evaluate differences in E.coli community composition across three standard water quality assessments including EPA Standard Method 1603, Colilert®, and mColiBlue24®.  Enterobacterial repetitive intergenic consensus sequence-polymerase chain reaction (ERIC-PCR) fingerprinting was used to characterize a collection of over 1100 isolates from five diverse water samples.  This study will help to identify possible community differences seen using various isolation techniques and their possible implications on MST applications.