Most Vibrio species in autochthonous marine microbial communities, such as Vibrio alginolyticus, Vibrio harveyi, Vibrio anguillarum among others, are considered nonpathogenic for humans. However, because many bacterial virulence genes are located in mobile genetic elements, the acquisition of mobile DNA could mediate the appearance of virulent or more virulent strains even in a species defined as nonpathogenic. In this study, we screened a collection of marine nonpathogenic Vibrio strains isolated in the area of the Venetian Lagoon for the presence of virulence and fitness genes usually present in Vibrio cholerae and Vibrio parahaemolyticus clinical isolates. More than one-third of the strains tested positive for the presence of at least one of the potential virulence/fitness genes with the gene encoding the V. cholerae neuraminidase the most frequently detected. Moreover, 13 of the environmental strains carried modified versions of the V. cholerae pathogenicity island VPI-2, and four of them also contained partial fragments of the V. parahaemolyticus Vp-PAI. The data obtained support the view of nonpathogenic Vibrio strains as a significant reservoir of virulence and fitness genes. The emergence of environmental bacteria with new virulence traits might constitute a direct concern for public health and a risk for human health.

Editor: Riks LaanbroekKeywords Vibrio parahaemolyticus environmental strains; T3SS2 genes in Vibrio parahaemolyticus marine strains; bacterial pathogenicity; virulence genes in marine bacteria; surveillance of potentially pathogenic Vibrio parahaemolyticus. AbstractVibrio parahaemolyticus-mediated disease has traditionally been associated with two virulence factors, thermostable direct haemolysin (TDH) and TDH-related haemolysin (TRH), which are present in most clinical isolates. Recently, it has been suggested that other virulence-related factors, such as some type III secretion system (T3SS) proteins, urease and DNA-methyltransferase, among others, might also play a role in disease caused by this bacterial species and have been shown to be carried by clinical, but not by environmental strains. Screening for a number of virulence and virulence-related genes in a collection of V. parahaemolyticus strains isolated from the Italian Adriatic coast indicates that in addition to the trh-positive strains isolated (6%), a significant percentage (18%) of these strains contain one or more genes with a possible role in pathogenicity. Specifically, some of the V. parahaemolyticus strains described in this study are the first environmental strains ever detected carrying T3SS2 genes. Data obtained by reverse transcription-PCR on environmental strain RNA indicate that at least some of these genes are functional. On the basis of the results obtained, it is suggested that such strains might constitute an environmental reservoir of genes possibly contributing to V. parahaemolyticus pathogenicity and to the spread, in the marine environment, of virulence-related genes usually found in clinical strains.

Increased intestinal permeability and abnormal motility were frequent without evidence of bacterial translocation in cirrhosis even without ascites. They are likely to be facilitators for bacterial translocation and thus precede it.

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