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Characterization of virulence profiles and antimicrobial resistance patterns of clinical and environmental Vibrio parahaemolyticus isolated in Canada Liu, Jennifer


Vibrio parahaemolyticus is a naturally occurring marine organism with a worldwide distribution in estuaries and coastal environments. Consequently, V. parahaemolyticus bio-accumulates in the gut of filter-feeding molluscan shellfish (e.g. oysters) and is a common cause of seafood associated gastroenteritis. Recent data show increased rates of V. parahaemolyticus infection in Canada, particularly British Columbia (BCCDC, 2015; PHAC, 2014). To further improve our understanding of the types of V. parahaemolyticus strains that exist in the Canadian (primarily British Columbia) environment and facilitate assessment of risk to public health, virulence profiles and antimicrobial resistance (AMR) patterns were determined for 600 isolates collected between 1998 and 2011. Clinical isolates (n=64) and environmental strains (n=536) cultured from oysters collected from Canadian growing areas were analyzed in this study. A multiplex PCR assay was used to confirm all isolates as V. parahaemolyticus and characterize virulence gene profiles (tdh and trh). AMR phenotypes were determined by a disc diffusion assay using a panel of 20 clinically relevant antibiotics. Further sub-typing using multi-locus sequence typing (MLST) was conducted on a subset (clinical, n=31; environmental, n=135) of isolates. Results showed 53% of clinical and 8% of environmental isolates possess at least one of the virulence markers. Overall levels of AMR were low, with 7% of isolates exhibiting pansusceptibility and 0.5% displaying resistance to 4 antibiotics. Ampicillin resistance was widespread (91%) with resistance to cephalothin (29%), streptomycin (4.3%), sulfisoxazole (2.7%), piperacillin (2.3%), oxolinic acid (0.5%), ceftiofur (0.4%), gentamicin (0.2%), and kanamycin (0.2%) also seen. MLST analysis showed the V. parahaemolyticus population structure is genetically diverse with 36 novel sequence types (STs) identified, all recovered from environmental isolates. In comparison, a smaller number of STs appear to be responsible for illnesses in British Columbia. Generally, findings from this research provide evidence that differences in virulence, AMR, and STs exist among clinically and environmentally derived V. parahaemolyticus. Future investigations using more discriminatory analyses, such as whole genome sequencing, may elucidate other factors and/or predictors of V. parahaemolyticus virulence as well as mechanisms mediating antibiotic resistance; this may facilitate studies attempting to understand the interplay between virulence and AMR.

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