Comparative genomic analysis of vibrio cholerae el tor preseventh and seventh pandemic strains isolated in various periods

Abstract

Genetic organization of 52 Vibrio cholerae El Tor biotype preseventh and seventh pandemic strains isolated in various periods was studied by PCR assay and DNA-DNA hybridization. It was established that the genome of most ancient of analyzed strains isolated from a diarrhea patient in 1910 was devoid of CTX and RS1 prophages, vibrio pathogenicity islands (VPI and VPI-2), and pandemic islands (VSP-1 and VSP-2) that contain key virulence genes. The appearance of pathogenic properties in cholera vibrios for the first time causing a local outbreak of cholera in 1937 is connected with the acquisition of VPI and CTX that carried genes tcpA and ctxAB, respectively, which are responsible for the colonization of the small intestine and encode the production of cholera toxin. The appearance of the seventh pandemic agent for cholera was shown to correlate with the acquisition by its precursor of two additional blocks of genes VSP-1 and VSP-2. This finding strongly supports the involvement of these genes in formation of the pandemic potential in the strains. Molecular typing methods allowed elucidation of differences in the genetic organization between prepandemic and pandemic strains. The detected variability of the genome of contemporary virulent strains may be a reason for the occurrence of etiological agent of cholera with new properties.

A Method for the Simultaneous Detection of Vibrio cholerae Strains and Drug-Resistant Genes in their Genome by Real-Time PCR

“…Clinical V. cholerae strains of the O1 serogroup El Tor biovar isolated before 1993 did not carry the floR, dfrAl, qnrVC (qnrVC1), or tetR genes (see Table 1). The obtained PCR results correspond to the data from the disc diffusion method and the literature data showing high sensitivity of the prepandemic and clinical V. cholerae O1 biovar El Tor, isolated during this period of the current pandemic [11,23] to the AMD. At the same time, 88% (14 of 16) of the clinical V. cholerae strains of biovar El Tor isolated after 1993 carried floR and dfrAl genes (possibly due to the presence of the SXT element in the genome).…”

“…According to the literature, V. cholerae biovar El Tor strains with multiple (>3) drug resistances were registered in the 1990s [11,12]. Indeed, according to the obtained information, the toxigenic V. cholerae biovar El Tor strains imported into Krasnodar, Kazan and Dagestan in 1993 were resistant to tetracycline, chloramphenicol, and trimethoprim.…”

A study of the distribution of regulatory genes controlling an expression of virulence genes among strains of Vibrio cholerae biovar eltor differing in their pandemic potential

“…The differences revealed between three groups of strains determine the stages of evolution of the cholera vibrio genome, which are connected with the acquisition of several genes by the avirulent precursor via a horizontal transfer of genetic information. At first, the key structural pathogenicity genes included in PIs (VPI-1 and VPI-2) and prophages CTX ϕ and RSI ϕ were acquired, then the genome acquired pandemicity islands VSP-1 and VSP-2 [3]. These data coincide in general with the results of other studies concerning the evolution of the cholera eltor genome.…”

“…The PCR analysis of the avirulent pandemic strain ATCC14033 was especially interesting, because this strain, being a representative of the biovar eltor which was discovered more than 100 yeas ago, can be consid- Note: The ctxA, ace, and zot genes, encoding the biosynthesis of the A-subunit of the cholera toxin, and the Ace and Zot toxins, respectively, are the parts of the CTXϕ prophage; the tcpA gene, determining the production of the toxin-coregulated adhesion pili, is located in the VPI-1 pathogenicity island; the mshA gene, involved in the biosynthesis of the mannose-sensitive adhesion pili, is a part of the EPI persistence island; deo0175 with tnp0183, and pro0490 with pro0496 genes are genetic markers of the VSP-1 and VSP-2 pandemicity islands, respectively. All data were obtained by the authors of this study [3].…”

“…An allocation of many key regulatory genes in mobile genetic elements allows us to propose that epidemically dangerous strains of V. cholerae biovar eltor are developed from the avirulent ancestor after it have acquired both structural pathogenicity genes and regulatory systems which control their expression. Recently, we demonstrated the molecular-genetic differences between the avirulent strain of V. cholerae biovar eltor, that was isolated in 1910, prepandemic clinical strains, that were able to provoke only local cholera episodes in 1937, and strains isolated during the 7th global cholera pandemic [3]. The differences revealed between three groups of strains determine the stages of evolution of the cholera vibrio genome, which are connected with the acquisition of several genes by the avirulent precursor via a horizontal transfer of genetic information.…”