A study of the prevalence of regulatory genes controlling virulence gene expression among Vibrio choleraeeltor biovariant strains varying in their pandemic potential
Smirnova, N.I.; Nefedov, K.S.; Osin, A.V.; Livanova, L.F.; Krasnov, I.M.
Molekuliarnaia Genetika Mikrobiologiia i Virusologiia 2007(1): 15-22
2007
ISSN/ISBN: 0208-0613 PMID: 17354604 Document Number: 612524
The evolution of the genome of the pathogenic agent of the seventh cholera pandernia Vibrio cholerae eltor biovariant was thought to occur by acquiring not only structural genes of virulence but also regulatory systems as a result of horizontal transfer events. The polymerase chain reaction revealed the presence of the following regulatory genes that control the virulence gene expression in the chromosome of pre-pandemic and pandemic strains of cholera vibrios eltor: toxR, toxT, tcpP, tcpH, luxS, luxO, crp, vicH, pepA. The avirulent V. cholerae strain ATCC 1,1033 isolated in 19 10 (hypothetical predecessor of the cholera eltor agent) was shown to be lacking the regulatory genes toxT, tcpP, tcpH localized in the pathogenicity island VPI-1, and to be capable of realizing positive control over the expression of the virulence genes involved in the ToxR regulon. The virulent strains isolated from cholera patients during the local cholera outbreak in Indonesia in 1937 did not differ from the strains that caused cholera eltor pandemic in 1961. The strains had identical content of the regulatory genes tested. Only one strain of the four isolates studied contained no tcpP gene. Two key regulatory genes, toxR and toxT, were sequenced in all the isolates. The toxR nucleotide sequence of three pre-pandemic strains was shown to be indistinguishable from that of the pandemic isolates. On the other land, the clinical strain MAK757 isolated prior to the emergence of the epidemic demonstrated an altered nucleotide sequence in its toxR gene. Experiments with the intra-intestinal challenge of suckling rabbits were indicative of similar virulence levels for the pre-pandemic and pandernic clinical strains. These results may serve as tile evidence of the in vivo activity of the pre-pandemic strains of the toxT, tepH, and tcpP positive regulatory genes that acquired in V. cholerae during the evolutionary process.