CLOSE PROXIMITY OF THE TDH, TRH AND URE GENES ON THE CHROMOSOME OF VIBRIO-PARAHAEMOLYTICUS

The distribution and location of the virulence-factor genes of Vibrio parahaemolyticus, tdh and trh, and the structural gene of urease, ureC , were examined on the genomic DNAs of 115 clinical isolates of V. par ahaemolyticus. The majority of strains (81%) had two copies of tdh on the chromosome, and no copies of trh or ure. Southern hybridization wi th a tdh probe, after pulsed-field gel electrophoresis of NotI-digeste d genomic DNA of each strain revealed only single bands, suggesting th at the two copies of tdh exist on single NotI fragments in each strain . Of the 115 strains, 7% had the tdh, trh and ure genes on chromosomal DNA. The three genes were also detected on single NotI fragments in t hese strains. More detailed analysis revealed that the three genes wer e localized within 40 kb. By long and accurate polymerase chain reacti ons (LA-PCR), the distance between trh and ure was shown to be less th an 8.5 kb. These results reveal a close proximity of the tdh, trh and ure genes on the chromosome of pathogenic V. parahaemolyticus strains.