Marine environment and human health: a whole genomic analysis and evaluation of the pathogenic potential of V.parahaemolyticus strains isolated from Northern Italian seawaters and carrying virulence genes

Disease outbreaks related to the marine environment appear to be escalating worldwide and growing number of human bacterial infections have been associated with recreational areas and commercial uses of marines resources. Because of the increasing human dependence on marine environments for fisheries, aquaculture, waste disposal and recreation, the potential for pathogen emergence from ocean ecosystems requires investigation. Particular challenge are the potential expansion of existing-marine indigenous pathogens and the emergence of new pathogens derived from autochthonous marine strains which have acquired new virulence traits via horizontal genetic transfer. The increasing consume of marine food products, the appearance and worldwide spread of new clones of Vibrio parahaemolyticus with pandemic potential and reporting, in very recent years, of some human infection cases caused by non pathogenic vibrios species, are some examples. The scope of this study has been to compare environmental and clinical Vibrio parahaemolyticus strains from the genetic point of view and to evaluate the pathogenic potential of the environmental strains. The bacterial strains deeply studied in this doctoral thesis were isolated from the Northern Adriatic Sea in the context of the international VibrioSea Project, aimed to develop a satellite-based early warning system to predict and prevent water-borne diseases in the Mediterranean Sea. The environmental V. parahaemolyticus strain collection was characterized performing a molecular genotyping to investigate whether the strains isolated in different geographical sites or in different periods of the year were clonally related and if it would be possible to identify clones persisting in time and/or different geographic sites. Considering globally the results obtained with 4 molecular typing methods (ribotyping, PFGE, REP-PCR and ERIC-PCR) and serotyping it has been possible to identify a number of bacterial genetic clusters persisting in the area also for long periods of time. On the contrary, a correlation between the type of sample or a geographic site and specific genetic patterns, has not been established. The contemporary use of different genotyping methods proved to be an effective approach allowing the grouping of genetically related strains also discriminating, on the basis of small differences, bacteria presenting very similar genetic profiles. In the second part of the study, the pathogenic potential of the environmental strains was evaluated adopting a genomic approach applying standard protocols, such as PCR, but also the innovative computational method Insignia which enabled the detection of a series of environmental strains carrying a pathogenicity island including several virulence-related genes. The subsequent in vitro analysis of the ability of representative environmental strains to adhere to and to cause cell damage in eukaryotic cells confirmed the pathogenic capability of the marine strains. On the basis of the data obtained it emerges that the marine environment represents a reservoir of bacteria carrying virulence genes thus constituting a public health concern and a risk to human health.