Abstract
Vibrio vulnificus is a bacterium responsible for severe gastroenteritis, sepsis and wound infections. Gastroenteritis and sepsis are commonly associated with the consumption of raw oysters, whereas wound infection is often associated with the handling of contaminated fish. Although classical virulence factors of this emerging pathogen are well characterised, there remains a paucity of knowledge regarding the general biology of this species. To investigate the presence of previously unreported virulence factors, we applied whole genome sequencing to a panel of ten V. vulnificus strains with varying virulence potentials. This identified two novel type 6 secretion systems (T6SSs), systems that are known to have a role in bacterial virulence and population dynamics. By utilising a range of molecular techniques and assays we have demonstrated the functionality of one of these T6SSs. Furthermore, we have shown that this system is subject to thermoregulation and is negatively regulated by increasing salinity concentrations. This secretion system was also shown to be involved in the killing of V. vulnificus strains that did not possess this system and a model is proposed as to how this interaction may contribute to population dynamics within V. vulnificus strains. In addition to this intra-species killing, this system also contributes to the killing of inter bacterial species and may have a role in the general composition of Vibrio species in the environment.
Highlights
V. vulnificus is a Gram negative opportunistic pathogen typically isolated from marine and coastal environments [1]
V. cholerae (Fig 1A) contains two hcp genes, which are distributed across chromosomes 1 and 2 whereas the sole hcp gene of V. vulnificus T6SS1 is located within the type 6 secretion systems (T6SSs) operon on chromosome 2 (Fig 1B)
T6SSs have been characterised in many Vibrio species, this is the first report, to our knowledge, of a functional T6SS in V. vulnificus
Summary
V. vulnificus is a Gram negative opportunistic pathogen typically isolated from marine and coastal environments [1]. The bacterium is capable of causing an array of disease symptoms such as gastroenteritis, wound infection and primary septicaemia [2]. Wound infection is commonly associated with recreational activities in contaminated water or handling of infected fish and can present with edema, bullae, cellulitis and necrotising fasciitis [2]. Unlike wound infections which have on average a 25% mortality rate, primary septicaemia, which is often associated with the consumption of contaminated seafood, has a greater than 50% mortality rate rising to 100% without the prompt administration of antibiotic therapy [1]. In America, the bacterium is the leading cause of seafood related deaths, and due to climate change causing an increase in surface sea temperature, PLOS ONE | DOI:10.1371/journal.pone.0165500. In America, the bacterium is the leading cause of seafood related deaths, and due to climate change causing an increase in surface sea temperature, PLOS ONE | DOI:10.1371/journal.pone.0165500 October 31, 2016
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