Bacterial and Vibrio community diversity in tropical rock oysters in northern Australia

Tropical rock oyster aquaculture is an emerging industry for most countries in the Asia-Pacific, including tropical north Australia. Food safety is an important element, but there exist large gaps in our understanding of the risks posed by potential pathogens including virulent Vibrio strains. To start to address this, oysters were collected from 13 sites across northern Australia to measure their bacterial community, including Vibrio. The dominant bacterial families were the Spirochaetaceae, Mycoplasmataceae and Vibrionaceae. The most abundant Vibrio species were V. parahaemolyticus, V. harveyi and V. diabolicus, but other potential human pathogenic species were detected including V. vulnificus. V. parahaemolyticus levels were above recommended guidelines in 37 % of oysters but virulence genes trh or tdh were not detected; V. vulnificus was detected in 31 % of oyster samples. Eleven potential oyster Vibrio pathogens were identified. Our results show that although food safety Vibrio species were prevalent, virulence genes were not. This highlights the need to focus on virulence rather than species abundance to obtain a realistic measure of risk.