An estuarine neritid gastropod, Clithon corona, a potential reservoir of thermostable direct hemolysin-producing Vibrio parahaemolyticus

Effect of sunlight and salinity on the survival of pathogenic and non-pathogenic strains of Vibrio parahaemolyticus in water microcosms

The effect of sunlight and salinities (10, 20, 39, and 60 psu) on the survival of Vibrio parahaemolyticus strains carrying either (thermostable direct hemolysin) tdh, the (thermostable related hemolysin) trh, and both or none of them were studied in water microcosms stabilized at 20°C using plate count agar and acridine orange direct viable count. All V. parahaemolyticus strains exposed to sunlight rapidly lose their culturability and evolve into a viable but non-culturable state (VBNC). However, the tdh positive strains remain more culturable than the non-virulent or trh positive strain but statically insignificant. At tested salinities, the survival time was higher at 10, 20, and 60 psu compared with that observed in seawater (39 psu). In seawater under dark condition, Vibrio strains remain culturable for up to 200 days with a significant difference between strains (p < 0.05). Furthermore, the non-pathogenic strain survives longer than the virulent ones. At different salinities, a better adaptation is observed at 10 and 20 psu compared with 39 and 60 psu. Resuscitations essays performed on VBNC bacteria in a nutrient broth at 20°C and 37°C does not show any revivification. PRACTITIONER POINTS: Effect of sunlight and salinities on the survival of V. parahaemolyticus in the marine environment. Resuscitation essay performed on viable but no cultivable bacteria. Microscope motility examines show that all strains exposed to sunlight remain motile after the loss of cultivability.

What genomic sequence information has revealed about Vibrio ecology in the ocean--a review

To date, the genomes of eight Vibrio strains representing six species and three human pathogens have been fully sequenced and reported. This review compares genomic information revealed from these sequencing efforts and what we can infer about Vibrio biology and ecology from this and related genomic information. The focus of the review is on those attributes that allow the Vibrios to survive and even proliferate in their ocean habitats, which include seawater, plankton, invertebrates, fish, marine mammals, plants, man-made structures (surfaces), and particulate matter. Areas covered include general information about the eight genomes, each of which is distributed over two chromosomes; a discussion of expected and unusual genes found; attachment sites and mechanisms; utilization of particulate and dissolved organic matter; and conclusions.

Soft-agar-coated filter method for early detection of viable and thermostable direct hemolysin (TDH)- or TDH-related hemolysin-producing Vibrio parahaemolyticus in seafood

A novel method for detecting viable and thermostable direct hemolysin (TDH)-producing or TDH-related hemolysin (TRH)-producing Vibrio parahaemolyticus in seafood was developed. The method involved (i) enrichment culture, selective for viable, motile cells penetrating a soft-agar-coated filter paper, and (ii) a multiplex PCR assay targeting both the TDH gene (tdh) and TRH gene (trh) following DNase pretreatment on the test culture to eradicate any incidental DNAs that might have been released from dead cells of tdh- or trh-positive (tdh+ trh+) strains and penetrated the agar-coated filter. A set of preliminary laboratory tests performed on 190 ml of enrichment culture that had been inoculated simultaneously with ca. 100 viable cells of a strain of tdh+ trh+ V. parahaemolyticus and dense populations of a viable strain of tdh- and trh-negative V. parahaemolyticus or Vibrio alginolyticus indicated that the method detected the presence of viable tdh+ trh+ strains. Another set of preliminary tests on 190 ml of enrichment culture that had been initially inoculated with a large number of dead cells of the tdh+ trh+ strain together with dense populations of the tdh- and trh-negative strains confirmed that the method did not yield any false-positive results. Subsequent quasi-field tests using various seafood samples (ca. 20 g), each of which was experimentally contaminated with either or both hemolysin-producing strains at an initial density of ca. 5 to 10 viable cells per gram, demonstrated that contamination could be detected within 2 working days.