CabA May Hold Key to Reducing Food-borne Illnesses Caused by Vibrio vulnificus

By targeting CabA, an extracellular matrix protein essential for biofilm formation, it may be possible to reduce the incidence of food-borne illnesses caused by the potentially lethal Vibrio vulnificus (V. vulnificus) marine bacterium found in biofilms on oyster shells and meat, according to the results of a study published recently in the International Journal of Food Microbiology.

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The majority of globally reported seafood-related deaths are attributable to infection with V. vulnificus, with death occurring as quickly as a day or two after symptom onset.

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V. vulnificus is primarily transmitted to humans through ingestion of contaminated oysters, and more than 90% of infections that result in V. vulnificus septicemia have been associated with the ingestion of oysters that were raw or undercooked.

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The specialized and highly differentiated three-dimensional communities of bacteria encased in an extracellular polymeric matrix, collectively referred to as biofilms, can harbor pathogenic and potentially lethal marine bacterium known to contaminate shellfish, such as V. vulnificus. Although a variety of methods have been developed to reduce the levels of this pathogenic bacteria in oysters after they have been harvested, a reliable means of ensuring safety for human consumption has been elusive, possibly due to the inability to remove V. vulnificus embedded in the biofilms that form on oyster shells and meat. Because the extracellular matrix protein CabA has been shown to be essential for biofilm formation,

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it may serve as an attractive target for postharvest decontamination strategies designed to attack the structure of the biofilm itself, and therefore reduce or eliminate the presence of V. vulnificus.

A study examining the role of CabA in the resistance of V. vulnificus-harboring biofilms to decontamination strategies was presented by first author Jin Hwan Park, PhD, from the National Research Laboratory of Molecular Microbiology and Toxicology, Department of Agricultural Biotechnology, and Center for Food Safety and Toxicology in Seoul, South Korea at the time of publication (presently at the Department of Microbiology and Environmental Toxicology at the University of California - Santa Cruz), and his colleagues. In describing the motivation for their research, Park et al stated that, "... biofilms are problematic in the food industry as major sources of recalcitrant contaminations, causing food spoilage and public health problems such as outbreaks of foodborne pathogens. Therefore, understanding the mechanisms involved in the formation of biofilms and maintenance of their structural integrity has become one of the most important concerns in food safety communities in order to develop efficient strategies to decontaminate biofilms in foods and food processing facilities."

Using a variety of techniques, study results revealed that CabA was required for the resistance of biofilms to decontamination strategies in vitro, and that cabA expression was induced in cells bound to oyster meat and shells. Additionally, CabA contributed to biofilm formation on oyster meat and shells, limited the detachment and disinfection of biofilms on oyster meat and shells, and consolidated biofilm structures on oyster shells.

In discussing the results generated from the experiments conducted in their study, Park et al said that, "... this study demonstrated that CabA, an extracellular matrix protein of the V. vulnificus biofilms, is induced upon binding of the pathogen to oysters. The cabA mutant was significantly defective in the development of biofilms on the oyster meat and shells. Furthermore, compared to the wild-type biofilm, the cabA mutant biofilm was more susceptible to detachment by vibration and disinfection by NaOCl on oysters as well as in vitro. It appears that CabA contributes to the formation of filaments in the biofilm matrix where the filaments connect bacterial cells together to build robust biofilms that are resistant to decontamination strategies."

Regarding the broader implications of the study’s results, Park et al stated, "... the results of this study will be useful to design an effective postharvest process program to reduce the pathogen in oysters and further ensure the safety of oysters."

William Perlman, PhD, CMPP is a former research scientist currently working as a medical/scientific content development specialist. He earned his BA in Psychology from Johns Hopkins University, his PhD in Neuroscience at UCLA, and completed three years of postdoctoral fellowship in the Neuropathology Section of the Clinical Brain Disorders Branch of the National Institute of Mental Health.

References

1. Park JH, Lee B, Jo Y, Choi SH. Role of extracellular matrix protein CabA in resistance of Vibrio vulnificus biofilms to decontamination strategies. Int J Food Microbiol. 2016;236:123—129.
2. Jones MK, Oliver JD. Vibrio vulnificus: disease and pathogenesis.Infect Immun. 2009;77:1723—1733.
3. Oliver JD. The Biology of Vibrio vulnificus. Microbiol Spectr. 2015 Jun;3(3). doi: 10.1128/microbiolspec.VE-0001-2014.
4. Park JH, Jo Y, Jang SY, et al. The cabABC Operon Essential for Biofilm and Rugose Colony Development in Vibrio vulnificus. PLoS Pathog. 2015;11:e1005192.