Vibrio parahaemolyticus

VpMT1 dendrogram fragment.png

Vibrio parahaemolyticus inhabits coastal waters worldwide, and is the leading cause of seafood-associated gastroenteritis, most commonly following ingestion of contaminated raw oysters. Incidence peaks in warmer months, which correlates with seasonal increases in V. parahaemolyticus numbers in seawater and shellfish. Increasing seawater temperatures, combined with spread of a virulent serotype O4:K12 strain from the U.S. Pacific Northwest to the Atlantic coast, have contributed to a ca. 10-fold increase in infections in recent years (1). 

Since serotyping provides limited strain resolution, multiple DNA-based typing methods have been developed for V. parahaemolyticus epidemiology and monitoring strain dispersal (2). Pulsed-field gel electrophoresis (PFGE) provides high level resolution but is technically complex and time consuming. Multilocus sequence typing (MLST), examining SNPs in 7 relatively conserved housekeeping genes, has proven to be highly informative; e.g., demonstrating the spread of ST36 strains (correlated with serotype O4:K12) to New England states where they represented nearly 50% of clinical isolates (3). Whole genome sequencing enhances strain resolution by extending MLST to the core genome (cgMLST). However, since MLST and cgMLST are costly, and length-based methods such as PFGE and multilocus variable number of tandem repeats analysis have intrinsically limited data portability, alternative sequence-based typing methods are needed.

Polymorphic locus sequence typing (PLST) targets tandem repeat-containing loci which undergo insertion/deletion at relatively high frequency while also accumulating SNPs within both repeat and flanking regions. Consequently, PLST of a single locus can provide, at lower cost and more rapid turnaround, resolution exceeding MLST and approaching cgMLST. At MicrobiType, the locus VpMT1 has been identified as an ideal target for V. parahaemolyticus PLST, yielding diversity index ≥0.99 and correlating strongly with epidemiological data (for dendrograms and further details see poster presented at the 2018 International Association for Food Protection meeting). 

Samples are conveniently submitted as heat-inactivated colonies (see Submission Guidelines; contact MicrobiType with inquiries regarding submission of alternative samples including enrichments). Results are confidentially reported as VpMT1 sequence, with clustal alignment and dendrogram illustrating the relationship of submitted sample to additional samples from your lab and to representative strains from GenBank.

(1) Urquhart EA et al. 2016. Environmental conditions associated with elevated Vibrio parahaemolyticus concentrations in Great Bay Estuary, New Hampshire. PLoS One 11:e0155018.
(2) Espejo RT et al. 2017. Insight into the origin and evolution of the Vibrio parahaemolyticus pandemic strain. Front Microbiol 8:1397.
(3) Xu F et al. 2015. Genetic characterization of clinical and environmental Vibrio parahaemolyticus from the Northeast USA reveals emerging resident and non-indigenous pathogen lineages. Front Microbiol 6:272.

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