MOLECULAR-GENETIC PROPERTIES OF VIBRIO CHOLERAE EL TOR STRAINS CIRCULATING IN AFRICA.

The review contains some brief information on cholera epidemics in Africa. Based on the results of the whole genome sequencing of 30 clinical strains isolated in Africa in different periods of the 7th cholera pandemic (1985-2012), extensive genetic diversity has been revealed. It is demonstrated that at present cholera epidemics in Africa are caused by new variants of the agent, which emerged in South- Eastern Asia in consequence of not only new genes acquisition, but also genome alterations of pandemicity and pathogenicity islands. SNP analysis of 53 strains circulating at different times in the territory of the continent, as well as isolated in South-Eastern Asia, has been carried out. Phylogenetic relations between the majority of the African and Asian strains have been established. In addition, strains were shown to exist that are, apparently, endemic to the African region. Identified genetic diversity of the strains with varying virulence and drug resistance points out the necessity of continuous molecular monitoring of the cholera agent in Africa.

[EVALUATION OF FUNCTIONAL FEATURES AND STRESS RESISTANCE OF ISOGENIC TOXIGENIC AND NON-TOXIGENIC BIOVAR EL TOR VIBRIO CHOLERAE STRAINS].

AIM: Comparative evaluation of functional features of toxigenic biovar El Tor Vibrio cholerae strains and their spontaneous non-toxigenic mutants and study of their resistance to saline and oxidative stress. MATERIALS AND METHODS: 8 biovar El Tor V. cholerae strains were studied: 4 clinical strains isolated in 1970 from patients in Astrakhan and 4 spontaneous non-toxigenic mutants of these strains that have lost cholera toxin genes as a result of residence in river water at the temperature of 25°C. Protein composition was determined in polyacrylamide gel electrophoresis by Laemmli U.K. Stress resistance of the strains was studied by adding H2O2 to 20 mM concentration and NaCl to 3 mM concentration to the cultural suspension. RESULTS: Loss of cholera toxin genes was shown to be accompanied by changes in the level of expression of 17 proteins including those that take part in energy metabolism, glucose transport, chemotaxis and purine bases. Moreover, non-toxigenic strains were established to be 5-15 times more resistant to saline and oxidative stress compared with toxigenic strains. CONCLUSION: Non-toxigenic V. cholerae mutants adopt better to stress factors, therefore the loss of cholera toxin gene in water environment could be one of the methods of adaptation of pathogenic bacteria to changes in the environment.

[Differences in virulence genes in Vibrio cholerae eltor strains isolated from different sources in Turkmenistan territory]. / Otlichiia v sostave genov virulentnosti v shtammakh Vibrio cholerae eltor, vydelennykh iz raznykh istochnikov na territorii Turkmenistana.

Polymerase chain reaction (PCR) detected the presence of various genes associated with virulence in genome of strains V. cholerae eltor isolated in Turkmenistan territory during epidemic and epidemic-free perios. It was found that a complete set of virulence genes (ctxA+, tcpA+ and toxR+) contained strains isolated from patients, carriers and environment only in cholera epidemics. Strains isolated from the environment in the period free of epidemics did not contain ctxA and tcpA in 78.2% of cases, but 5.2% of the strains carried a complete set of virulence genes. There were also nontoxigenic strains containing genes tcpA and toxR. Such strains were isolated from the environment (16.6%) and vibrion carriers (42.9%). Isolated were also strains V.cholerae eltor carrying bacteriophage CTX phi with incomplete set of virulence genes and having genotype ctxA-, ace+ and zot+. Almost all the strains ctxA-, tcpA+ carry attRS1-site in genome. This shows that such strains may transform into toxigenic as a result of infection with bacteriophage CTX phi.

[Prevalence of major virulence genes among various Vibrio cholerae El-TOR strains for evaluating their epidemiological significance]. / Izuchenie rasprostrannennosti osnovnykh genov virulentnosti sredi razlichnykh shtammov Vibrio cholerae El-TOR dlia opredeleniia ikh épidemicheskoi znachimosti.

Specific oligonucleotide primers were chosen for identifying the fragments of the four major virulence genes of V. cholerae eltor (ctxA, tcpA, toxR, and hap) using the polymerase chain reaction (PCR). In order to estimate the efficiency of complex PCR testing of V. cholerae for evaluation of their epidemiological significance, a collection of 80 V. cholerae eltor strains with known virulence was selected, whose most important specific features had been studied previously. The hap was appropriate species-specific gene making it possible to detect V. cholerae strains regardless of their virulence. The most complete and objective data for evaluating the epidemic significance can be obtained by detecting the presence of three virulence genes (ctxA, tcpA, and toxR) in their chromosome. The prevalence of the above four genes in various V. cholerae strains isolated from the environment during epidemic and non-epidemic periods was studied.

[Molecular genetic features of Vibrio cholerae classica strains, that caused the Asiatic cholera epidemic in Russian in 1942]. / Molekuliarno-geneticheskie osobennosti shtammov Vibrio cholerae classica, vyzvavshikh épidemiiu Aziatskoi kholery v Rosii v 1942 g.

Molecular genetic features of Vibrio cholerae classical strains which caused an epidemic of Asian cholera in Russia in 1942 have been studied for the first time. These strains had a high level of choleric toxin production and toxin-coregulated adhesion piles, the main virulence factors; all the strains were auxotrophs and needed purine and/or amino acids for growth in minimal medium. Moreover, having hapA structural gene in the chromosome (according to polymerase chain reaction), they did not produce soluble hemagglutinin protease promoting propagation of vibrios in the environment. These features of natural V. cholerae classical strains are apparently responsible for the peculiar infectious and epidemic processes in the cholera epidemic.

[Characterization of Vibrio cholerae eltor isolates according to their epidemic potential using new diagnostic cholera bacteriophages eltor ctx+ and ctx- and by the polymerase chain reaction]. / Differentsiatsia isoliatov Vibrio cholerae eltor po ikh épidemicheskoi znachimosti s pomoshch'iu novykh diagnosticheskikh kholernykh bakteriofagov él'tor ctx+ i ctx- i polimeraznoi tsepnoi reaktsii.

The epidemic potential of 113 V. cholerae eltor strains of different origin was determined with new diagnostic cholera bacteriophages eltor ctx+ and ctx-, as well as the test for hemolytic activity. Of these strains 50 were epidemically safe and 51 were epidemically dangerous, while the epidemic potential of 12 other strains could not be detected. Determination of genes ctxA, tcpA and toxR in the strains under study by means of the polymerase chain reaction (PCR) revealed that epidemically dangerous strains carried the whole set of the above genes in 92.2% of cases. 98.0% of epidemically safe cultures were lacking either gene ctxA, or genes ctxA and tcpA, or genes ctxA, tcpA and toxR, which confirmed their incapacity to cause cholera. The results of the differentiation of the cultures with new diagnostic cholera phages coincided with the results of PCR in 90% of cases. The most complete and reliable evaluation of the epidemic potential of individual vibrio isolates may be obtained using the two compared methods. The amplification test system gives more information when isolates with unclear epidemic potential are analyzed.