Isolation and characterisation offrom fish examined postmortem at ZSL London Zoo between 2014 and 2018.

Abstract

BACKGROUND: When suspectwere cultured from fish at ZSL London Zoo, investigations were carried out to determine whether they were possible causes of cholera. METHODS: Bacterial culture was carried out on fish examined postmortem and colonies were identified using standard techniques including the API 20NE biochemical test kits. Suspect isolates were submitted to the Public Health England laboratory for additional testing. Separately, a number of fish were submitted for routine histopathology. RESULTS: On 13 occasions between 2014 and 2018, suspectedwere cultured from individuals of eight different freshwater fish species. Archived cultures for eight of these (from six different fish species) were investigated and seven isolates (from five fish species) were confirmed as, but all were non-O1, non-O139 strains. Whole-genome sequencing showed that the five fish species had uniquemultilocus sequence types (three isolates fromwere identical), all of which were genetically distant from human isolates. CONCLUSIONS: There was no evidence that these isolates could cause cholera. Histopathological changes consistent with vibriosis were seen in several fish, suggesting thatwere causing the disease, but there were also concurrent infections or predisposing stress factors.