Isolation and characterisation of Vibrio cholerae from fish examined postmortem at ZSL London Zoo between 2014 and 2018

Abstract

BackgroundWhen suspect Vibrio cholerae were cultured from fish at ZSL London Zoo, investigations were carried out to determine whether they were possible causes of cholera.MethodsBacterial 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.ResultsOn 13 occasions between 2014 and 2018, suspected V cholerae were 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 V cholerae, but all were non-O1, non-O139 strains. Whole-genome sequencing showed that the five fish species had unique V cholerae multilocus sequence types (three isolates from Aphanius danfordii were identical), all of which were genetically distant from human isolates.ConclusionsThere was no evidence that these isolates could cause cholera. Histopathological changes consistent with vibriosis were seen in several fish, suggesting that V cholerae were causing the disease, but there were also concurrent infections or predisposing stress factors.

Bacterial Co-Infection as a Potential Threat to Farmed Flathead Grey Mullet (Mugil cephalus): Phenotypic and Molecular Diagnosis, Histopathology, Immunity Response, and In Vitro Antibacterial Evaluation

“…These pathogens are plentiful in aquatic environments, where they are free-living in water or in association with aquatic fauna, considering opportunistic pathogens in many aquatic animals, such as marine fishes, crustaceans, and bivalves [11,12]. In addition, many Vibrio species have been implicated as causes of human foodborne illnesses as V. cholerae, V. parahaemolyticus, V. vulnificus, and V. alginolyticus are associated with gastroenteritis, severe dehydration, and primary septicemia due to the consumption of contaminated drinking water and undercooked or raw sea food [13,14]. Moreover, the relationship between Vibrio spp.…”

“…Naturally, fish have a mutualistic relationship with V. cholera as this bacterium secretes proteases and chitinases, with which they digest food (e.g., chitin and protein) in the fish gut [13,14,28]. Previous studies have reported the isolation of V. cholerae from the internal organs of diseased ayu (Plecoglossus altivelis) and guppy fish (Poecilia reticulate) in Japan and Iran, respectively [29][30][31], as well as from Nile tilapia (Oreochromis niloticus) that were cultured in floating cages in Thailand [32].…”