Genetic relatedness of Escherichia coli isolates in interstitial water from a Lake Huron (Canada) beach

Abstract

Research was undertaken to characterize Escherichia coli isolates in interstitial water samples of a sandy beach on the southeastern shore of Lake Huron, Ontario, Canada. A survey of the beach area revealed the highest abundance of E. coli in interstitial water of the foreshore beach sand next to the swash zone. Higher concentrations of E. coli (up to 1.6 x 10(6) CFU/100 ml of water) were observed in the interstitial water from the sampling holes on the beach itself compared to lake water and sediment. Repetitive extragenic palindromic PCR (REP-PCR) was used to characterize the genetic diversity of E. coli isolates from interstitial water samples on the beach. E. coli isolates from the same sampling location frequently exhibited the same REP-PCR pattern or were highly similar to each other. In contrast, E. coli isolates from different sampling locations represented populations distinct from each other. This study has identified a unique ecological niche within the foreshore area of the beach where E. coli may survive and possibly multiply outside of host organisms. The results are of interest as increasing concentrations of E. coli in recreational waters are often considered to be an indication of recent fecal pollution.

FIG. 1.

Map of study area and 12 sampling sites.

FIG. 2.

(A) Surface map of E. coli levels in lake water. (B) Surface map of conductivity of lake water over the Eighteen Mile River study area on 30 August 2005.

FIG. 3.

Dendrogram of REP-PCR DNA fingerprints of E. coli isolates obtained from interstitial water. The code beside each fingerprint on the right-side y axis is the unique identifier of each isolate. The bottom lane of each dendrogram shows the 100-bp molecular size markers. The scale on the top x axis shows percent similarity between the isolates as determined by Bionumerics software.