Strain variability and pathogenic potential of tdhcarrying Vibrio parahaemolyticus isolated from diseased Penaeus monodon

Coordination of primary metabolism and virulence factors expression mediates the virulence of Vibrio parahaemolyticus towards cultured shrimp (Penaeus vannamei)

AIMS

Acute hepatopancreatic necrosis disease (AHPND) caused by Vibrio parahaemolyticus has emerged as a severe bacterial disease of cultured shrimp. To identify the key virulence factors, two AHPND-causing V. parahaemolyticus (Vp_AHPND ) strains (123 and 137) and two non-Vp_AHPND strains (HZ56 and ATCC 17082) were selected.

METHODS AND RESULTS

Challenge tests showed that the four strains exhibited different virulence towards shrimp with cumulative mortalities at 48 h postinfection (hpi) ranging from 10 to 92%. The expression of pirAB^VP in strain 123 and 137 was not significantly different. Genomic analysis revealed that the two Vp_AHPND strains contain a plasmid with the PirAB^VP toxins (pirAB^VP ) flanked by the insertion sequence (ISVal1) that has been identified in various locations of chromosomes in Vp_AHPND strains. The two Vp_AHPND strains possessed almost identical virulence factors, while ISVal1 disrupted three genes related to flagellar motility in strain 137. Phenotype assay showed that strain 123 possessed the highest growth rate and swimming motility, followed by strain 137, suggesting that the disruption of essential genes mediated by ISVal1 significantly affected the virulence level. Transcriptome analysis of two Vp_AHPND strains (123 and 137) further suggested that virulence genes related to the capsule, flagella and primary metabolism were highly expressed in strain 123.

CONCLUSIONS

Here for the first time, it is demonstrated that the virulence of Vp_AHPND is not only determined by the expression of pirAB^VP , but also is mediated by ISVal1 which affects the genes involved in flagellar motility and primary metabolism.

SIGNIFICANCE AND IMPACT OF THE STUDY

The genomic and transcriptomic analysis of Vp_AHPND strains provides valuable information on the virulence factors affecting the pathogenicity of Vp_AHPND.

Tropical shrimp aquaculture farms harbour pathogenic Vibrio parahaemolyticus with high genetic diversity and Carbapenam resistance

In characterization of food borne pathogens from the environment, assessment of virulence, genetic diversity and AMR are essential preludes to formulate preventive strategies and to combat the spread. This study aimed to identify and characterize pathogenic Vibrio parahaemolyticus in the coastal aquaculture farms of Kerala, India. Twenty-seven β-haemolytic V. parahaemolyticus were isolated from 7 out of 40 farms studied. Among the 27 isolates, 15 possessed the tdh gene and 4 had trh. ERIC PCR and PFGE illustrated the presence of pathogenic isolates that shared genetic similarity with clinical strains. One pathogenic isolate was identified to be multidrug resistant (MDR) and 59% exhibited a MAR index of 0.2 or above. Seventy four percent of the pathogenic isolates were ESBL producers and 3.7% of them were carbapenemase producers phenotypically. This asks for adoption of control measures during farming to prevent the transmission of pathogenic V. parahaemolyticus to the environment and food chain.