Genetic elements carrying virulence and antibioticresistant genes: incidence and exchange mechanisms among microorganisms of the marine community also including allochthonous bacterial species of medical interest.

It is known that bacteria can acquire antimicrobial resistance (AR) and virulence genes by horizontal transfer of genetic elements and that antibiotic use selects for existing resistance mechanisms and for novel resistance mutations (Smith et al., 2002). Recently, some Vibrio cholerae clinical strains containing antibiotic resistance genetic elements previously detected in marine bacteria have been isolated (Pande et al., 2012). During previous studies conducted in our lab (Labella et al., 2013; Gennari et al., 2012; Caburlotto et al., 2010), a significant number of environmental bacteria carrying virulence genes and antibiotic resistant and multi-resistant marine bacterial strains were isolated from the coastal area of the Venetian lagoon and from a number of Italian fish farms. Data obtained in these studies support the view that the autochthonous marine micro-flora might constitute a reservoir of virulence and AR genes. Considering that most of those AR and virulence determinants are located in mobile genetic elements (MGE), they can be transferred to other bacteria by horizontal gene transfer (HGT). In particular, it is important to determine if HGT can occur in the marine environment not only among autochthonous bacteria, such as Vibrio, Aeromonas, Photobacterium, but also between members of the marine bacterial population and human pathogenic bacteria of medical interest transitorily present in seawaters. The first part of the PhD project has focused on the development of a DNA microarray to detect over 200 genes of medical and veterinarian interest in the marine environment. The device would represent an alternative method to PCRs, offering the advantage of interrogating a unique sample for thousands of loci. It would be useful for the screening of collections of marine bacterial strains or for monitoring changes in the bacterial community over time and areas. The aim of the second part of the study, made in collaboration with the PGBA team at the INRA-Tours Institute, has been to evaluate the possibility for marine bacteria to transfer MGEs to allochtonous bacteria present in the marine environment. In particular, conjugations were set up in different environmental conditions to verify the transfer of antibiotic resistance determinants from environmental Vibrio donor strains to members of medical interest of the Enterobacteriaceae family, and to better understand the horizontal gene transfer mechanism. An additional objective of the project has been to test the possibility for specific MGEs of mobilizing genetic elements involved in virulence and AR and lacking transfer autonomy.