Escherichia coli is one of the common inhabitant in the gastrointestinal tract of warm-blooded animals. The abundant nutrients available as well as the moderate temperature in the gastrointestinal tract might be one of the incentives for E. coli to adapt to the environment. It is believed that E. coli have lower survivability in external environments outside the host. However, there are reports that E. coli can survive for long periods and replicates in the external environment. Walk et al (2009) discovered five "Cryptic" Escherichia clades based on multilocus sequence typing (MLST) which were phenotypically indistinguishable from E. coli sensu stricto. They also discussed evidence that the cryptic clades II to VI has a better survival in environment outside the host than E. coli and clade I which is more host associated.
The watershed in Ting Kau has a distinct gradient of human impact where there is less influence of anthropogenic impacts in areas of higher altitude to the village and beach area in the bottom of the watershed. This watershed is chosen to examine the population of presumptive E. coli (possible presence of cryptic clades). The prevalence and genetic relatedness of E. coli and the cryptic clades in the area will also be investigated.