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E. coli bloom and capsule detection

E. coli ‘bloom’ events in Australian reservoirs and recreational waters are not uncommon. During these events, elevated E. coli counts from 10,000 to 100,000 cells/100ml of water have been reported.

While these counts are well above the safe levels specified in the Australian Drinking Water Guidelines (ADWG), research has shown that cell counts this high would require an unachievable level of faecal contamination.

Instead, the strains responsible may represent, free living E. coli of environmental origin.

The discovery of non-faecal, environmental E. coli forming blooms in reservoirs has the potential to adversely affect risk assessment processes for water utilities. For example, a positive E. coli test result from a reservoir will likely result in its closure and the release of public health notice and increased water treatment costs, even though it may be a harmless environmental strain.

We are the only Australian laboratory to offer a rapid DNA based analysis that can detect all known Australian encapsulated bloom strains.

Relatively few strains have been found to be responsible for E. coli bloom events, and all strains isolated from bloom events in Australia carry a capsule originating from Klebsiella.

Typically, environmental E. coli strains do not have pathogenic tendencies and are therefore less of a health risk than faecal-borne E. coli.

These bloom strains typically belong to phylogroups A1, C or B1 and carry both the galF gene and a Klebsiella capsule gene. This results in an environmentally adapted organism which produces a mucoid capsule. The capsule then protects the organism from exposure to treatment (Nanayakkara et al., 2018).

Three bloom forming strains (capsule types KL16, KL49 and KL53) have been associated with previously reported Australian east coast bloom strains. Five bloom forming strains (capsule types KL53, KL60, KL63 and KL101) have been associated with previously reported Australian west coast bloom strains.