Development and evaluation of polymorphic locus sequence typing for epidemiological tracking of Vibrio parahaemolyticus

Authors: EDLIND, TOM - Microbitype Llc; Richards, Gary

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/21/2019
Publication Date: 5/30/2019
Citation: Edlind, T., Richards, G.P. 2019. Development and evaluation of polymorphic locus sequence typing for epidemiological tracking of Vibrio parahaemolyticus. Foodborne Pathogens and Disease. https://doi.org/10.1089/fpd.2019.2649.
DOI: https://doi.org/10.1089/fpd.2019.2649

Interpretive Summary: Vibrio parahaemolyticus is a common bacterial inhabitant of estuarine waters where it may accumulate to relatively high levels in shellfish, including oysters that are commonly ingested raw. In humans, it is the leading cause of shellfish-borne bacterial disease, which has surged in recent years in regions such as the eastern United States as a consequence of warming coastal waters and introduction of virulent strains. Oyster beds implicated in human infection may be subject to extended closure with associated economic consequences. To unambiguously track down the source of infection and to monitor strain variation in the environment, a user-friendly and affordable typing method is needed. The development, evaluation, and commercial implementation of a technique known as polymorphic locus sequence typing (PLST) for the foodborne pathogens Listeria monocytogenes and Salmonella enterica were recently described. In this paper, we describe the development of a PLST method for tracking the source of Vibrio parahaemolyticus infections within the environment.

Technical Abstract: Vibrio parahaemolyticus is a common inhabitant of coastal estuaries and can accumulate to high levels in the shellfish that populate those waters. Human gastrointestinal infection occasionally follows ingestion of raw oysters and can lead to extended closures of implicated oyster beds with serious economic consequences. To track down the source of human infection, and to monitor strain variation in the environment, a user-friendly and affordable typing method that provides sufficient resolution for epidemiological analysis is needed. Polymorphic locus sequence typing (PLST) is based on conventional PCR and dideoxynucleotide sequencing of the one or two most phylogenetically informative genomic loci. Bioinformatic analyses of GenBank databases identified the V. parahaemolyticus polymorphic tandem repeat-containing loci VpMT1 and VpMT2 on chromosomes 1 and 2, respectively, as promising PLST targets, yielding diversity indexes of 0.99. Phylogenetic analysis identified multiple clusters representing strains known or likely to be epidemiologically related. Correlations with serotype and multilocus sequence type were strong but resolution was higher; e.g., North American ST36 strains yielded 16 VpMT1 alleles. In the laboratory, VpMT1 and VpMT2 were robust, resolving 16 of 17 strains following PCR and sequencing directly from heat-killed colonies. Finally, 4 of 13 retail oyster enrichments yielded VpMT sequences that were unique but closely related to previously characterized clinical or environmental V. parahaemolyticus isolates.