We investigated the virulence properties of four Vibrio parahaemolyticus strains causing acute gastroenteritis following consumption of indigenous mussels in Italy. The isolated strains were cytotoxic and adhesive but, surprisingly, lacked tdh, trh, and type three secretion system 2 (T3SS2) genes. We emphasize that nontoxigenic V. parahaemolyticus can induce acute gastroenteritis, highlighting the need for more investigation of the pathogenicity of this microorganism.
Vibrio parahaemolyticus infections cause acute, self-limiting gastroenteritis, typically characterized by diarrhea, abdominal cramps, nausea, vomiting, fever, and chills, lasting 1 to 3 days. The onset usually occurs within 24 h of eating contaminated food. Cases are most commonly reported during the warmer months and are often associated with eating raw or undercooked shellfish or other cooked foods that have been cross-contaminated with raw shellfish (22). Pathogenicity of this microorganism is attributed to the production of a thermostable direct hemolysin (TDH) and the TDH-related hemolysin (TRH) (13). Recently, type three secretion system 2 (T3SS2) of V. parahaemolyticus has been investigated as an additional potential indicator of strain virulence (2,8,17). Together, the tdh, trh, and T3SS2 genes are widely considered the predominant indicators of strain virulence for this microorganism (8). This is substantiated by the prevalence of these genetic markers in clinical V. parahaemolyticus isolates, as opposed to their infrequent detection in food and environmental samples (8).For this report, we characterized four V. parahaemolyticus strains lacking tdh, trh, and T3SS2 genes isolated as the sole pathogen from patients affected by acute gastroenteritis with indigenous mussels as the most probable source of infection. On 20 September 2010 in Torino (northern Italy), 4 people were hospitalized with acute gastroenteritis. The first case involved a healthy 47-year-old man (patient A), while a family group outbreak involved another three healthy individuals: a 55-year-old woman (patient B), a 59-year-old man (patient C), and a 58-year-old man (patient D). Epidemiological information reported that none of the patients had recently traveled to other countries and that on 19 September they had eaten home-cooked mussels, probably undercooked. Mussels involved in both the sporadic case and the outbreak came from the same Italian growing area (North Adriatic), but it was not possible to trace the specific lots. Patient A and patients B, C, and D developed diarrhea, fever, abdominal cramps, nausea, and vomiting about 13 h and about 18 h after mussel consumption, respectively. On admission, the patients were treated with intravenous hydration, and the symptoms ceased within 48 h without the need for antibiotic therapy.Stool specimens of patients were cultured on MacConkey agar, Salmonella-Shigella agar, Columbia blood agar, Hektoen agar, 5% sheep blood agar supplemented with ampicillin (30 g/ml) (ASBA 30), Yersinia cefsulodin-irgasan-novobiocin (CIN) agar (a...
