Serotype Distributions And Molecular Characteristics Of Vibrio Parahaemolyticus Isolates In Malaysia

Abstract

Vibrio parahaemolyticus is a gram-negative halophilic bacteria found mainly in the marine and estuarine environment. Cases of V.parahaemolyticus were mostly sporadic and associated with diverse serovars. The emergence of a pandemic serovar O3:K6 in 1996 however changed the epidemiology abruptly and has since accounted for V.parahaemolyticus outbreaks worldwide. In Malaysia, little information concerning the molecular epidemiology of this organism is known in spite of cases reported regionally. Therefore this study elucidates the serotype distribution and molecular characteristics of V.parahaemolyticus isolates in Malaysia. The strains studied were a collection of 17 clinical and 42 environmental isolates obtained from 1997 to 2007.

From this study, O3:K6 was the dominant serotype and was found only in clinical isolates. Other serotypes found in clinical isolates include O4:K68, O1:KUT, O3:K5 and O4:K8. The environmental isolates were different with O12:KUT, O3:KUT and O6:KUT as the major serotypes. Serotype O4:K68, O4:K8, O1:KUT, and O4:K12 were found in both clinical and environmental isolates. One environmental isolate was untypable by the O and K antisera. PCR results showed all clinical and environmental isolates were positive for the toxR gene. Based on its genotypic traits, the V.parahaemolyticus isolates were divided into four groups. Group I (tdh+, trh-, ORF8+, GS-PCR+), Group II (tdh+, trh-, ORF8-, GS-PCR-), Group III (tdh+, trh+, ORF8-, GS-PCR-) and Group IV (tdh-, trh-, ORF8-, GS-PCR-). Of this, 13 clinical isolates with serotype O3:K6 and O4:K68 falls into Group 1, thus belonging to the pandemic clone. Two clinical isolates were in Group II whereas one clinical isolate was in Group III. Interestingly one clinical isolate falls into Group IV which is similar for all environmental isolates. The DNA sequences of the PCR products when analysed using Basic Local Alignment Search Tool (BLAST) showed high sequence similarity when compared to published sequence in the GenBank. PFGE was performed to determine the genetic relatedness of the isolates. All clinical isolates in Group I belonged to PFGE Type 1 with 9 subtypes, making it the dominant pattern. These isolates exhibits the same molecular characteristics as the pandemic strains found in other countries. The environmental isolates produce more diverse patterns and were clearly different form the clinical isolates.

In conclusion, this study showed that the serotype distribution among the clinical isolates in Malaysia is stable within the last 10 years from 1997 to 2007, with O3:K6 as the dominant serotype. This serotype has been circulating in Malaysia as early as 1997. Although some serotypes were found in both clinical and environmental isolates, their molecular characteristics were totally different. None of the environmental isolates were positive for the toxin genes, ORF8 and GS-PCR. Finally, PFGE was shown to be more discriminative than serotyping and the two methods were not correlated.