Escherichia coli, a natural inhabitant of the intestinal guts of the warm-blooded animals, has developed a symbiotic relationship with the animal hosts. Therefore, it is believed that E. coli cannot survive and gradually die off once released into the natural environment. Thus, the occurrence of E. coli in waters has long been used as an indicator of fecal pollution worldwide, signalling the possibility of the presence of fecal pathogens. However, recent studies have reported that even in the absence of fecal contamination, E. coli could also be isolated from various environments such as rivers, soils and freshwater sediments. Furthermore, persistent populations were also observed over a period of time in the habitats mentioned above, seriously confounds the use of E. coli as a reliable...[ Read more ]

Escherichia coli, a natural inhabitant of the intestinal guts of the warm-blooded animals, has developed a symbiotic relationship with the animal hosts. Therefore, it is believed that E. coli cannot survive and gradually die off once released into the natural environment. Thus, the occurrence of E. coli in waters has long been used as an indicator of fecal pollution worldwide, signalling the possibility of the presence of fecal pathogens. However, recent studies have reported that even in the absence of fecal contamination, E. coli could also be isolated from various environments such as rivers, soils and freshwater sediments. Furthermore, persistent populations were also observed over a period of time in the habitats mentioned above, seriously confounds the use of E. coli as a reliable fecal pollution indicator. Although the aforementioned phenomenon has been extensively investigated, previous studies were largely focused on the freshwater systems. So far, while there are limited investigations on the existence of E. coli in marine environments, it is not well known whether or not these bacteria persist in marine habitats. In this study, an intertidal mudflat was chosen as a study site to first determine whether E. coli populations could be isolated throughout one-year monthly monitoring to understand the role of marine sediment as an environmental reservoir of E. coli. Seasonal variation in E. coli abundance was observed; the highest level, up to 641 CFU/100ml seawater and 823 CFU/100g sediment, were found during rainy months (April to June), and the lowest level, ≤10 CFU/100ml seawater or 100g sediment, occurred during dry months (November to March). Subsequently, we also propose to investigate the genetic diversity of E. coli, and examine which populations have survived in the intertidal mudflat. By utilizing phylogenetic grouping and repetitive sequence based-PCR (Rep-PCR) DNA fingerprint analyses, several unique E. coli populations were repeatedly found in seawater and sediment over time. To further confirm the uniqueness of E. coli genotype, multi-loci sequencing typing (MLST) analyse was performed to investigate the evolutionary relatedness of E. coli isolates. The sequencing results of E. coli isolates from cow feces and soil proved that certain populations in soil have undergone several genomic modifications and thus give rise to unique DNA fingerprints. This result indicates a high consistent and correspondent relationship between Rep-PCR DNA fingerprinting and MLST analyses, further verify the uniqueness of E. coli genotypes observed in seawater and sediment. These findings altogether suggested that E. coli are able to survive and mostly likely form self-sustaining and persistent populations in marine environment.