[The evaluation of the virulent properties of Vibrio cholerae O1 by using in-vitro methods]. / Otsenka virulentnykh svoistv Vibrio cholerae O1 s pomoshch'iu metodov in vitro.

The virulent properties of V. cholerae O1 (more than 1000 strains) were studied. For this purpose the following methods were used: the determination of hemolytic activity, the express method based on the determination of the speed of mannite oxidation, complex analysis and polymerase chain reaction (PCR). The comparative analysis of the results of the in vitro determination of virulence revealed that the most frequently occurring strains among the strains isolated from humans were vct+ strains (80.5%), hemolysis-negative strains (83.9%) which were virulent (faintly virulent) as determined by complex analysis (38.2%), cholerogenic as determined by the express method (60.2%). Among the strains isolated from the environment were vct- strains (87.4%), hemolysis-negative strains (63.2%) which were virulent as determined by complex (13.1%), as well as by the express method (74.3%). The data of the determination of the vct gene did not correlate with the results obtained by complex analysis. The use of complex analysis was expedient only in the detection of strains sensitive to eltor phage in the dilution routine test of V. eltor strains. The methods for the determination of virulence, available for practical laboratories, were Grieg's method for the determination of hemolytic activity and express method. PCR proved to reliable in vitro method for the determination of the vct gene.

[The reasons for the resistance of Vibrio cholerae to diagnostic phages]. / Prichiny ustoichivosti kholernykh vibrionov k diagnosticheskim fagam.

Phage resistance of 225 strains of cholera germs of O1 group obtained from different countries in 1988-1992 has been analyzed. Change of sensitivity to diagnostic phages was mostly connected with the decrease or loss of agglutinability in cholera sera. Phage resistance is rather conditioned by the change of the surface structures of the cell and by further change of phage reception zones. The increase in the number of strains sensitive to diagnostic phages after 6-12 months of storage evidenced for stabilization of cell wall structures and increase of their viability under relatively favourable conditions of storage.

[A case of the importation onto the territory of Russia of cholera caused by a new serovar]. / Sluchai zavoza na territoriiu Rossii kholery, vyzvannoi novym serovarom.

Materials on the import of rarely occurring Vibrio cholerae, not belonging to group O1 of serovar O139, to the territory of Russia are presented. The clinical picture of a cholera case is described and the biological properties of V. cholerae, serovar O139, are presented. A suggestion has been made concerning the appearance of a new V. cholerae serovar, capable of ousting V. cholerae eltor, the cause of the seventh pandemic.

[Genetic determination and the spectrum of the hemolytic activity of Vibrio cholerae: their significance in the complex of biovar-specific traits]. / Geneticheskoe determinirovanie i spektr gemoliticheskoi aktivnosti Vibrio cholerae: znachenie v komplekse biovarospetsificheskikh priznakov.

A collection of 363 V. cholerae strains isolated from different sources were studied by the spectrum of their hemolytic activity in combination with biovar-associated properties. The strains were analyzed for the presence of the cholera toxin (CT) gene (vct) and the hemolysin gene (hly) with the use of the CT probe and a previously cloned 6.56 kb fragment of V. eltor DNA coding the synthesis of hemolysin. The study revealed that all V. cholerae strains had the hly gene irrespective of the spectrum of their hemolytic activity, biovar, 01 agglutinability and the presence of the vct gene in their genome, while other species of the genus Vibrio and related groups contained no hly gene sequence. The results of the comparative study of the hemolytic activity of V. cholerae and V. eltor are discussed.

[Species specific DNA probes for identifying Vibrio cholerae]. / Vidospetsifichnyi DNK-zond dlia identifikatsii kholernykh vibrionov.

A 1.74 kb HindIII fragment from a Vibrio cholerae eltor library of genes was found to be strictly specific for Vibrio cholerae strains independent of the biotypes, serotypes and 01-agglutination ability. The fragment was cloned in pUC19 vector plasmid. The resultant recombinant plasmid pES78VCS was transformed into Escherichia coli strain HB101 resulting in construction of strain KM57. The sites for HincII and XhoI were plotted on a restriction map of the cloned fragment. Two HindIII-XhoI as well as one HincII-XhoI fragments appeared to be of the same specificity as the intact HindIII-HindIII one. The probe identifies 10(6) bacterial cells or 60 ng of purified chromosomal DNA of Vibrio cholerae and may be used for identification of 01 and non-01 strains.

[The virulence of Vibrio cholerae isolated under different epidemiological situations]. / O virulentnosti Vibrio cholerae, vydelennykh v razlichnykh épidemiologicheskikh situatsiiakh.

The virulence of V. cholerae isolated on the territory of Russia and other CIS countries from environmental objects and from humans in different epidemic situations during the period of 1987-1991 was studied. The analysis of the data obtained in this study revealed that intensive epidemic complications were linked with the realization of the pathogenic properties of strains, characterized by the presence of the ctx gene and the absence of hemolytic activity. As a rule, in single cases or in isolated group cases of cholera V. cholerae hemolysin-negative strains without the cholera toxin gene were isolated.

[Cholera in Ukraine and Moldova during the 7th pandemic]. / Kholera na Ukraine i v Moldove v period sed'moi pandemii.

The epidemic manifestations of cholera in the Ukraine and Moldova in 1970-1991 are analyzed. In the Ukraine the peak of cholera morbidity in 1970 was caused by infection brought to the ports of Odessa and Kerch with its subsequent spread to other territories. This infection was characterized by outbreaks transmitted through water, mainly sea water, with the isolation of Vibrio eltor toxigenic virulent strains and outbreaks of vibrio carriership of alimentary (dairy) origin with the isolation of avirulent strains. In Moldova local outbreaks of water origin were registered in 1970-1972. In both territories prolonged (up to 16 years and even longer) circulation of cholera vibrios, mainly nontoxigenic and avirulent, were registered. The retrospective epidemiological analysis and the epidemiological situation in some regions of the Ukraine in 1991 completely confirmed the prognostic importance of the division of territories into regions according to the type of epidemiological manifestations and the necessity of differentiating the measures to be taken in the system of epidemiological surveillance.

[Hemolysin from Vibrio cholerae eltor: cloning and expression of genes in Escherichia coli]. / Gemolizin Vibrio cholerae eltor: klonirovanie i ékspressiia genov v Escherichia coli.

A 6.56-kb V. cholerae eltor DNA fragment encoding hemolysin synthesis was cloned in pUC18. The resultant recombinant plasmid pES4H (9.25 kb) was mapped by restriction analysis and shown to express in different E. coli strains as well as in nonhemolytic V. cholerae strains. Application of the cloned fragment as a molecular probe revealed homologous sequences in all V. cholerae strains tested independently on their biotypes, hemolytic activity and presence of vct-genes in their genomes while none of other Vibrio species and related microorganisms contained such sequences. A recombinant E. coli strain, a V. cholerae eltor hemolysin producer, was constructed. The simultaneous expression of hemolytic and toxinogenic properties by the same V. cholerae strains is discussed.

[The composition of a population of cloned cultures of revertant Vibrio cholerae L forms]. / Izuchenie sostava populiatsii klonovykh kul'tur revertantov L-form kholernykh vibrionov.

The process of L-transformation and L-transformed state duration have been studied for their effect on variability of main characters of revertant cultures of choleric vibrions L-forms at the population level with the use of cloned cultures of the choleric vibrions. The study was conducted on two strains of the choleric vibrion of the eltor biovar in different periods of storage in the L-transformed state (1, 3, 6 months). It has been revealed that characters of the species and biovar remained stable despite the influence of L-transforming agents. The characters of clone cultures characterizing virulence (sensitivity to KhDF phages, hemolytic activity, toxin production and virulence for sucking rabbits proved to be subjected to variability to the greatest extent with simultaneous preservation of the toxin-production gene. A resistant change of the serovar (from Inaba to Ogava) is observed only in one revertant-subculture of the virulent strain.