[Genetic characterization of Vibrio parahaemolyticus O3: K6 serovariant isolated in Shenzhen]

To characterize the O3: K6 serovariant of Vibrio parahaemolyticus on virulence gene and molecular typing, and analyze the genetic relationship between O3: K6 and O3: K6 serovariants.

PFGE was performed on 115 strains of V.parahaemolyticus which were collected from the anal swab of cases of foodbrone diseases in Shenzhen during 2006-2012. According to isolation times and locations, 7 strains of O3: K6 were selected as control strains. Tdh gene, trh gene, orf8 gene were detected, GS-PCR, multi-locus sequence typing (MLST) were used to chracterize 7 strains of O3: K6 and O3: K6 serovariants.

PFGE indicated that 58.3% (67/115) of V. parahaemolyticus strains shared a high similarity of band pattern (similarity > 80%) , which comprised of O3: K6 (44/67), O1: KUT(4/67), and O3: K6 serovariants(19/67). Among the O3: K6 serovariants, O1: K25 accounted for 7% (5/67), O4: K68 accounted for 10% (7 /67), O11: K36 accounted for 10% (7 /67). They all carried both tdh and trh gene, and 53% (10/19) was GS-PCR positive and carried orf8 gene, 26% (5/19) was both GS-PCR and orf8 gene negative, 21% (4/19) was GS-PCR negative, orf8 gene positive, 89% (17/19) was assigned to ST-3, 11% (2/19) was assigned to ST-305. Seven strains of O3: K6 was GS-PCR positive, carried orf8 gene, assigned to ST-3. ST-305 and ST-3 had differences in 2 housekeeping genes, which was dtdS gene and pntA gene. In the 305th base of dtdS gene, ST-305(147 allele profile) was T, while ST-3(4 allele profile) was C. In the 33th base of pntA gene, ST-305(93 allele profile) was T, while ST-3(29 allele profile ) was C.

O4: K68,O1: K25 and O11: K36 were highly similar in virulencec gene carriage, MLST type of O3: K6, and aslo shared a close genetic relationship with O3: K6, thus were considered as O3: K6 serovirants.