Escherichia coli isolates were obtained from common host sources of fecal pollution and characterized by using repetitive extragenic palindromic (REP) PCR fingerprinting. The genetic relationship of strains within each host group was assessed as was the relationship of strains among different host groups. Multiple isolates from a single host animal (gull, human, or dog) were found to be identical; however, in some of the animals, additional strains occurred at a lower frequency. REP PCR fingerprint patterns of isolates from sewage (n ؍ 180), gulls (n ؍ 133), and dairy cattle (n ؍ 121) were diverse; within a host group, pairwise comparison similarity indices ranged from 98% to as low as 15%. A composite dendrogram of E. coli fingerprint patterns did not cluster the isolates into distinct host groups but rather produced numerous subclusters (approximately >80% similarity scores calculated with the cosine coefficient) that were nearly exclusive for a host group. Approximately 65% of the isolates analyzed were arranged into host-specific groups. Comparable results were obtained by using enterobacterial repetitive intergenic consensus PCR and pulsed-field gel electrophoresis (PFGE), where PFGE gave a higher differentiation of closely related strains than both PCR techniques. These results demonstrate that environmental studies with genetic comparisons to detect sources of E. coli contamination will require extensive isolation of strains to encompass E. coli strain diversity found in host sources of contamination. These findings will assist in the development of approaches to determine sources of fecal pollution, an effort important for protecting water resources and public health.
Racine, Wisconsin, located on Lake Michigan, experiences frequent recreational water quality advisories in the absence of any identifiable point source of pollution. This research examines the environmental distribution of Escherichia coli in conjunction with the assessment of additional parameters (rainfall, turbidity, wave height, wind direction, wind speed and algal presence) in order to determine the most probable factors that influence E. coli levels in surface waters. Densities of E. coli were highest in core samples taken from foreshore sands, often exceeding an order of magnitude greater than those collected from submerged sands and water. Simple regression and multivariate analyses conducted on supplementary environmental data indicate that the previous day's E. coli concentration in conjunction with wave height is significantly predictive for present-time E. coli concentration. Genetic fingerprinting using repetitive element anchored PCR and cellular fatty acid analysis were employed to assess the presence of clonal isolates which indicate replication from a common parent cell. There were relatively few occurrences of clonal patterns in isolates collected from water, foreshore and submerged sands, suggesting that accumulation of E. coli, rather than environmental replication, was occurring in this system. Non-point source pollution, namely transport of accumulated E. coli from foreshore sands to surface waters via wave action, was found to be a major contributor to poor recreational water quality at the Lake Michigan beaches involved in this study.
Bacterial strains were isolated from beach water samples using the original Environmental Protection Agency method for Escherichia coli enumeration and analyzed by pulsed-field gel electrophoresis (PFGE). Identical PFGE patterns were found for numerous isolates from 4 of the 9 days sampled, suggesting environmental replication. 16S rRNA gene sequencing, API 20E biochemical testing, and the absence of -glucuronidase activity revealed that these clonal isolates were Klebsiella, Citrobacter, and Enterobacter spp. In contrast, 82% of the nonclonal isolates from water samples were confirmed to be E. coli, and 16% were identified as other fecal coliforms. These nonclonal isolates produced a diverse range of PFGE patterns similar to those of isolates obtained directly from untreated sewage and gull droppings. -Glucuronidase activity was critical in distinguishing E. coli from other fecal coliforms, particularly for the clonal isolates. These findings demonstrate that E. coli is a better indicator of fecal pollution than fecal coliforms, which may replicate in the environment and falsely elevate indicator organism levels.
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