Prevalence and Virulence Properties of Non-O1 Non-O139 Vibrio Cholerae Strains from Seafood and Clinical Samples Collected in Italy

Seafood and clinical samples collected in Italy during 2006 were analyzed to evaluate prevalence, serological and virulence properties of non-O1 non-O139 Vibrio cholerae (NCV) isolates. Biochemical and serological characterization of the strains was performed by standardized procedures while virulence properties of NCVs were assayed by molecular, in vivo and in vitro toxicological methods. Of the 300 seafood samples examined, including mussel, cod, mackerel, anchovy, clam, prawn and cuttlefish, 5.6% were positive for NCVs: 4.7% and 8.5% from local and imported seafood, respectively. The prevalence of NCVs was highest in prawn (16.6%) and mussel (7.7%). Of 58 hospitalized patients that presented acute diarrhea, 3.4% eliminated NCVs in stools 24-48 h after consumption of seafood. All NCVs had ToxR and hlyAET genes but lacked ctxA, zot, and tcpA genes. One isolate from prawn had stn/sto gene. All strains were hemolytic, cytotoxic, and able to induce intestinal and extraintestinal effects on the suckling mouse model. Our results confirm that non-toxigenic NCVs that express the gene encoding El Tor-like hemolysin can be isolated from patients suffering a cholera-like syndrome after consumption of seafood. This evidence along with the virulence and enteropathogenicity of all the ctxA(-) tcpA(-) zot(-) stn/sto(-) hlyAET(+) NCV isolates in the experimental model, suggest that El Tor-like hemolysin may play an important role in human pathogenesis. Moreover, the isolates from seafood showed molecular, biological and enzymatic patterns similar to those isolated from clinical samples, underlining that environmental NCVs are potentially able to induce human infections and confirming the important role of seafood as a vehicle of V. cholerae diseases.