E. coli is widely used as an indicator of faecal contamination of water. The assumptions that it is unable to multiply outside a host and is not present in the absence of faecal contamination are among the criteria used for its selection as an indicator. However, a growing body of evidence suggests that E. coli can not only survive for long periods but also multiply outside a host, confounding its use as an ideal water quality indicator. E. coli strains that produce significantly elevated counts have been a regular occurrence in freshwater reservoirs and recreational lakes in Australia. These strains, termed E. coli bloom strains, belong to E. coli phylogenetic groups A and B1, and they all carry a capsule originating from Klebsiella. The elevated counts indicate that the bloom strains have a growth advantage and are able to outcompete the other co-occurring E. coli.

In my PhD I attempted to genotypically and phenotypically characterise these E. coli bloom strains. This included looking at key traits that could confer a growth rate advantage and hence a bloom status on an E. coli strain. As all bloom strains are encapsulated, the diversity and distribution of Klebsiella capsules in E. coli overall was investigated. In this talk I will discuss how important or not the capsule and other traits are for the bloom strains.