Genotypic Diversity of Escherichia coli in the Water and Soil of Tropical Watersheds in Hawaii

Abstract

High levels of Escherichia coli were frequently detected in tropical soils in Hawaii, which present important environmental sources of E. coli to water bodies. This study systematically examined E. coli isolates from water and soil of several watersheds in Hawaii and observed high overall genotypic diversity (35.5% unique genotypes). In the Manoa watershed, fewer than 9.3% of the observed E. coli genotypes in water and 6.6% in soil were shared between different sampling sites, suggesting the lack of dominant fecal sources in the watershed. High temporal variability of E. coli genotypes in soil was also observed, which suggests a dynamic E. coli population corresponding with the frequently observed high concentrations in tropical soils. When E. coli genotypes detected from the same sampling events were compared, limited sharing between the soil and water samples was observed in the majority of comparisons (73.5%). However, several comparisons reported up to 33.3% overlap of E. coli genotypes between soil and water, illustrating the potential for soil-water interactions under favorable environmental conditions. In addition, genotype accumulation curves for E. coli from water and soil indicated that the sampling efforts in the Manoa watershed could not exhaust the overall genotypic diversity.Comparisons of E. coli genotypes from other watersheds on Oahu, Hawaii, identified no apparent grouping according to sampling locations. The results of the present study demonstrate the complexity of using E. coli as a fecal indicator bacterium in tropical watersheds and highlight the need to differentiate environmental sources of E. coli from fecal sources in water quality monitoring.

Distribution and Characterization of Salmonella enterica Isolates from Irrigation Ponds in the Southeastern United States

“…However, most strains (70%) belonged to only 7 DTs. Overlap of DTs for strains from both water and sediment samples indicated the potential interaction of water and sediments, consistent with the 33% overlap of E. coli genotypes between soil and water (48). Populations of Salmonella may be ecoregion specific in that 63% of strains did not cluster with any reference strain from the national database but were genetically more similar to isolates derived from this study or from other aquatic sources in Georgia and Florida.…”

Spatial and Temporal Variation in Enterococcal Abundance and Its Relationship to the Microbial Community in Hawaii Beach Sand and Water

“…This could be attributed to the different survivabilities of E. coli and enterococci, especially in the high-salinity marine environments (39). Furthermore, E. coli itself has also been recognized as a member of indigenous microbial communities in various environments (40)(41)(42).…”

Correlation of Intracellular Trehalose Concentration with Desiccation Resistance of Soil Escherichia coli Populations

“…By constructing a soil E. coli library for the Manoa watershed, numerous E. coli strains were frequently found at different sampling locations and on different sampling dates (19). These soil E. coli strains are thus considered naturalized soil E. coli populations and are expected to have higher desiccation resistance than E. coli populations from other sources.…”

“…Studies using molecular tools have detected unique genotypic compositions of E. coli populations in soil (6,19,23), and the persistence of certain E. coli strains over extended periods of time in soils further supports the notion that certain soil E. coli populations are naturalized members of indigenous soil microbial communities (23). Since soil-sourced E. coli cells may enter nearby waterways in the absence of actual fecal inputs and thus generate false signals of fecal pollution, intense debate has arisen regarding the suitability of E. coli as a fecal indicator in water quality monitoring.…”