[Etiologic characteristics of Vibrio parahaemolyticus strains causing outbreaks and sporadic cases in Guangdong, 2013]

To study the serotypes, antimicrobial resistance, virulence genes and molecular characteristics of Vibrio parahaemolyticus isolated from outbreaks and sporadic cases in Guangdong, 2013.36 Vibrio parahaemolyticus strains isolated from outbreaks and 43 strains from sporadic cases were sero-typed and tested for antimicrobial resistance. PCR was used to detect for tdh(thermostable direct hemolysin gene), trh (tdh(-) related hemolysin gene), GS-PCR and orf8 genes. All the samples were analyzed by pulsed-field gel electrophoresis (PFGE).36 isolates from outbreaks were all identified as O3 : K6, and among the 43 sporadic isolates, O3 : K6 (23, 53.49%) was the dominant serotype. Vibrio parahaemolyticus isolates showed high resistance rate to ampicillin (96.20%) and cefalotin (40.50%), but were high sensitive to cotrimoxazole (100%) and chloramphenicol (100%). 83.33% (30/36) outbreak isolates were resistant to multi-drugs but only 37.21% (16/43) of the sporadic isolates showed so. Results from virulence gene detection suggested that all the 36 outbreak isolates belonged to tdh(+) trh(-) strains, while 86.05% (37/43) of the sporadic isolates were tdh(+)trh(-) and 11.63% (5/43)were tdh(-)trh(+) . Only one tdh(+)trh(+) strain was found. All the outbreak isolates contained GS-PCR and/or orf8 genes, whereas among the sporadic isolates only 51.16% (22/43) of them carrying the similar genes. Results from PFGE analysis suggested that 79 isolates were discriminated into 3 clusters and 32 different PFGE patterns with the similarity value between 59.8% and 100.0%. Outbreak isolates seemed to gather in the same cluster, while the sporadic isolates spreading in all the three clusters.O3 : K6 was the dominant serotype in Vibrio parahaemolyticus strains isolated in Guangdong, 2013. These strains showed high sensitivity to most antibiotics, but with multi-drug resistance. Positive rate of tdh gene was high, and most O3 : K6 strains contained GS-PCR and/or orf8 genes. PFGE analysis revealed genetic diversity was within the Vibrio parahaemolyticus strains in Guangdong.