Molecular Insights Into the Evolutionary Pathway of Vibrio cholerae O1 Atypical El Tor Variants

Pandemic V. cholerae strains in the O1 serogroup have 2 biotypes: classical and El Tor. The classical biotype strains of the sixth pandemic, which encode the classical type cholera toxin (CT), have been replaced by El Tor biotype strains of the seventh pandemic. The prototype El Tor strains that produce biotype-specific cholera toxin are being replaced by atypical El Tor variants that harbor classical cholera toxin. Atypical El Tor strains are categorized into 2 groups, Wave 2 and Wave 3 strains, based on genomic variations and the CTX phage that they harbor. Whole-genome analysis of V. cholerae strains in the seventh cholera pandemic has demonstrated gradual changes in the genome of prototype and atypical El Tor strains, indicating that atypical strains arose from the prototype strains by replacing the CTX phages. We examined the molecular mechanisms that effected the emergence of El Tor strains with classical cholera toxin-carrying phage. We isolated an intermediary V. cholerae strain that carried two different CTX phages that encode El Tor and classical cholera toxin, respectively. We show here that the intermediary strain can be converted into various Wave 2 strains and can act as the source of the novel mosaic CTX phages. These results imply that the Wave 2 and Wave 3 strains may have been generated from such intermediary strains in nature. Prototype El Tor strains can become Wave 3 strains by excision of CTX-1 and re-equipping with the new CTX phages. Our data suggest that inter-chromosomal recombination between 2 types of CTX phages is possible when a host bacterial cell is infected by multiple CTX phages. Our study also provides molecular insights into population changes in V. cholerae in the absence of significant changes to the genome but by replacement of the CTX prophage that they harbor.     

Hemolytic Vibrio cholerae O1 that is sensitive to Mukerjee's cholera phage IV and the phage produced by the hemolytic vibrio lysogenized with the infection of Mukerjee's cholera phage IV

Strains of hemolytic Vibrio cholerae O1 (El Tor vibrio) which are sensitive to Mukerjee's cholera phage group IV were isolated from cholera patients in North-East Thailand in 1986. Plaques of the phage on these hemolytic V. cholerae O1 were usually translucent but almost transparent on some strains, just like the plaques on non-hemolytic V. cholerae O1 (classical vibrio). These hemolytic V. cholerae O1 were lysogenized with the infection of cholera phage IV, and the lysogenized strains produced phage different from cholera phage IV. These hemolytic strains were classified into Cured type in prophage typing of V. cholerae O1, El Tor, because they were also lysogenized with Kappa phage and were hemolytic. When Cured-type V. cholerae O1, El Tor previously isolated in various countries were examined for the sensitivity to cholera phage IV, some of the isolates were sensitive.     

Genome Sequence of Hybrid Vibrio cholerae O1 MJ-1236, B-33, and CIRS101 and Comparative Genomics with V. cholerae

The genomes of Vibrio cholerae O1 Matlab variant MJ-1236, Mozambique O1 El Tor variant B33, and altered O1 El Tor CIRS101 were sequenced. All three strains were found to belong to the phylocore group 1 clade of V. cholerae, which includes the 7th-pandemic O1 El Tor and serogroup O139 isolates, despite displaying certain characteristics of the classical biotype. All three strains were found to harbor a hybrid variant of CTXΦ and an integrative conjugative element (ICE), leading to their establishment as successful clinical clones and the displacement of prototypical O1 El Tor. The absence of strain- and group-specific genomic islands, some of which appear to be prophages and phage-like elements, seems to be the most likely factor in the recent establishment of dominance of V. cholerae CIRS101 over the other two hybrid strains.Vibrio cholerae, a bacterium autochthonous to the aquatic environment, is the causative agent of cholera, a life-threatening disease that causes severe, watery diarrhea. Cholera bacteria are serogrouped based on their somatic O antigens, with more than 200 serogroups identified to date (6). Only toxigenic strains of serogroups O1 and O139 have been identified as agents of cholera epidemics and pandemics; serogroups other than O1 and O139 have the potential to cause mild gastroenteritis or, rarely, local outbreaks. Genes coding for cholera toxin (CTX), ctxAB, and other virulence factors have been shown to reside in bacteriophages and various mobile genetic elements. In addition, V. cholerae serogroup O1 is differentiated into two biotypes, classical and El Tor, by a combination of biochemical traits, by sensitivity to biotype-specific bacteriophages, and more recently by nucleotide sequencing of specific genes and by molecular typing (5, 17, 19).There have been seven pandemics of cholera recorded throughout human history. The seventh and current pandemic began in 1961 in the Indonesian island of Sulawesi and subsequently spread to Asia, Africa, and Latin America; the six previous pandemics are believed to have originated in the Indian subcontinent. Isolates of the sixth pandemic were almost exclusively of the O1 classical biotype, whereas the current (seventh) pandemic is dominated by the V. cholerae O1 El Tor biotype as the causative agent, a transition occurring between 1923 and 1961. Today, the disease continues to remain a scourge in developing countries, confounded by the fact that V. cholerae is native to estuaries and river systems throughout the world (8).Over the past 20 years, several new epidemic lineages of V. cholerae O1 El Tor have emerged (or reemerged). For example, in 1992, a new serogroup, namely, O139 of V. cholerae, was identified as the cause of epidemic cholera in India and Bangladesh (25). The initial concern was that a new pandemic was beginning; however, the geographic range of V. cholerae O139 is currently restricted to Asia. Additionally, V. cholerae O1 hybrids and altered El Tor variants have been isolated repeatedly in Bangladesh (Matlab) (23, 24) and Mozambique (1). Altered V. cholerae O1 El Tor isolates produce cholera toxin of the classical biotype but can be biotyped as El Tor by conventional phenotypic assays, whereas V. cholerae O1 hybrid variants cannot be biotyped based on phenotypic tests and can produce cholera toxin of either biotype. These new variants have subsequently replaced the prototype seventh-pandemic V. cholerae O1 El Tor strains in Asia and Africa, with respect to frequency of isolation from clinical cases of cholera (27).Here, we report the genome sequence of three V. cholerae O1 variants, MJ-1236, a Matlab type I hybrid variant from Bangladesh that cannot be biotyped by conventional methods, CIRS101, an altered O1 El Tor isolate from Bangladesh which harbors ctxB of classical origin, and B33, an altered O1 El Tor isolate from Mozambique which harbors classical CTXΦ, and we compare their genomes with prototype El Tor and classical genomes. From an epidemiological viewpoint, among the three variants characterized in this study, V. cholerae CIRS101 is currently the most “successful” in that strains belonging to this type have virtually replaced the prototype El Tor in Asia and many parts of Africa, notably East Africa. This study, therefore, gives us a unique opportunity to understand why V. cholerae CIRS101 is currently the most successful El Tor variant.     

Household Transmission of Vibrio cholerae in Bangladesh

Background

Vibrio cholerae infections cluster in households. This study''s objective was to quantify the relative contribution of direct, within-household exposure (for example, via contamination of household food, water, or surfaces) to endemic cholera transmission. Quantifying the relative contribution of direct exposure is important for planning effective prevention and control measures.

Methodology/Principal Findings

Symptom histories and multiple blood and fecal specimens were prospectively collected from household members of hospital-ascertained cholera cases in Bangladesh from 2001–2006. We estimated the probabilities of cholera transmission through 1) direct exposure within the household and 2) contact with community-based sources of infection. The natural history of cholera infection and covariate effects on transmission were considered. Significant direct transmission (p-value<0.0001) occurred among 1414 members of 364 households. Fecal shedding of O1 El Tor Ogawa was associated with a 4.9% (95% confidence interval: 0.9%–22.8%) risk of infection among household contacts through direct exposure during an 11-day infectious period (mean length). The estimated 11-day risk of O1 El Tor Ogawa infection through exposure to community-based sources was 2.5% (0.8%–8.0%). The corresponding estimated risks for O1 El Tor Inaba and O139 infection were 3.7% (0.7%–16.6%) and 8.2% (2.1%–27.1%) through direct exposure, and 3.4% (1.7%–6.7%) and 2.0% (0.5%–7.3%) through community-based exposure. Children under 5 years-old were at elevated risk of infection. Limitations of the study may have led to an underestimation of the true risk of cholera infection. For instance, available covariate data may have incompletely characterized levels of pre-existing immunity to cholera infection. Transmission via direct exposure occurring outside of the household was not considered.

Conclusions

Direct exposure contributes substantially to endemic transmission of symptomatic cholera in an urban setting. We provide the first estimate of the transmissibility of endemic cholera within prospectively-followed members of households. The role of direct transmission must be considered when planning cholera control activities.     

Characterization of Vibrio cholerae O1 isolates responsible for cholera outbreaks in Kenya between 1975 and 2017

Kenya is endemic for cholera with different waves of outbreaks having been documented since 1971. In recent years, new variants of Vibrio cholerae O1 have emerged and have replaced most of the traditional El Tor biotype globally. These strains also appear to have increased virulence, and it is important to describe and document their phenotypic and genotypic traits. This study characterized 146 V. cholerae O1 isolates from cholera outbreaks that occurred in Kenya between 1975 and 2017. Our study reports that the 1975–1984 strains had typical classical or El Tor biotype characters. New variants of V. cholerae O1 having traits of both classical and El Tor biotypes were observed from 2007 with all strains isolated between 2015 and 2017 being sensitive to polymyxin B and carrying both classical and El Tor type ctxB. All strains were resistant to Phage IV and harbored rstR, rtxC, hlyA, rtxA and tcpA genes specific for El Tor biotype indicating that the strains had an El Tor backbone. Pulsed field gel electrophoresis (PFGE) genotyping differentiated the isolates into 14 pulsotypes. The clustering also corresponded with the year of isolation signifying that the cholera outbreaks occurred as separate waves of different genetic fingerprints exhibiting different genotypic and phenotypic characteristics. The emergence and prevalence of V. cholerae O1 strains carrying El Tor type and classical type ctxB in Kenya are reported. These strains have replaced the typical El Tor biotype in Kenya and are potentially more virulent and easily transmitted within the population.     

El Tor型CTXΦ对O1群不同霍乱弧菌的转染性研究

研究丝状噬菌体CTXΦ对O1群不同霍乱弧菌的水平转移效率及菌株的噬菌体免疫能力。利用带有氯霉素抗性基因遗传标记的CTXETΦ感染颗粒对O1群的4株不同霍乱弧菌进行体外和体内转染实验,根据氯霉素抗性筛选转染子,通过Southern Blot等方法进行验证并判断CTXΦ基因组的存在形式,计算比较不同菌株的转染率,分析转染及噬菌体免疫机制。带有遗传标记的CTXETΦ对古典型霍乱弧菌1119的体内转染率高于体外;体内转染实验中,古典菌株1119的转染率远高于其它3株El Tor型霍乱弧菌;在El Tor型霍乱弧菌中,不含rstR基因的IEM101的转染率高于另外两株带有rstR基因的霍乱弧菌2~3个数量级。古典型霍乱弧菌比El Tor型菌株对CTXETΦ噬菌体颗粒更易感,TCP菌毛的表达和rstR基因介导的噬菌体免疫影响CTXΦ在霍乱弧菌中的水平转移。     

The Population Structure of Vibrio cholerae from the Chandigarh Region of Northern India

Background

Cholera infection continues to be a threat to global public health. The current cholera pandemic associated with Vibrio cholerae El Tor has now been ongoing for over half a century.

Methodology/Principal Findings

Thirty-eight V. cholerae El Tor isolates associated with a cholera outbreak in 2009 from the Chandigarh region of India were characterised by a combination of microbiology, molecular typing and whole-genome sequencing. The genomic analysis indicated that two clones of V. cholera circulated in the region and caused disease during this time. These clones fell into two distinct sub-clades that map independently onto wave 3 of the phylogenetic tree of seventh pandemic V. cholerae El Tor. Sequence analyses of the cholera toxin gene, the Vibrio seventh Pandemic Island II (VSPII) and SXT element correlated with this phylogenetic position of the two clades on the El Tor tree. The clade 2 isolates, characterized by a drug-resistant profile and the expression of a distinct cholera toxin, are closely related to the recent V. cholerae isolated elsewhere, including Haiti, but fell on a distinct branch of the tree, showing they were independent outbreaks. Multi-Locus Sequence Typing (MLST) distinguishes two sequence types among the 38 isolates, that did not correspond to the clades defined by whole-genome sequencing. Multi-Locus Variable-length tandem-nucleotide repeat Analysis (MLVA) identified 16 distinct clusters.

Conclusions/Significance

The use of whole-genome sequencing enabled the identification of two clones of V. cholerae that circulated during the 2009 Chandigarh outbreak. These clones harboured a similar structure of ICEVchHai1 but differed mainly in the structure of CTX phage and VSPII. The limited capacity of MLST and MLVA to discriminate between the clones that circulated in the 2009 Chandigarh outbreak highlights the value of whole-genome sequencing as a route to the identification of further genetic markers to subtype V. cholerae isolates.     

Cholera at the beginning of the XXI century. Prognosis

The worldwide epidemiological situation in cholera El Tor at the beginning of this century is presented; among its characteristic features are continued extensive epidemics and outbreaks in African and Asian countries with cases of import of this infection to other continents. Outbreaks caused by a new variant of the infective agent of cholera, Vibrio cholerae O139, are still registered at limited territories in the countries of South-East Asia. In some CIS countries (Azerbaijan, Kazakhstan and Russia) unstable situation in cholera is still preserved due to cases of infection import mainly from Asian countries, as well as to the isolation of epidemically insignificant haemolysin-positive and haemolysin-negative V. cholerae O1 and O139, containing no ctx and tcpA genes, from surface water reservoirs and other environmental objects. In Russia prognosis for cholera is still unfavorable.     

Role of normal microflora in the treatment of vibrio carrier state in rat gnotobionts]

Materials on the study of interactions between Vibrio cholera El Tor and some indigenous bacteria of human intestinal tract, which proved to be active antagonists in vitro, are presented in this work. Experiments were conducted on gnotobiotic rats (Fisher), using various combinations and variants of the order of the microorganism administration; there were revealed no antagonistic relations between Virbrio cholerae El Tor and Escherichia coli M-17, Lactobacillus fermenti, Lactobacillus plantarum. Vibrio cholera El Tor disappeared completely from the intestinal tract of the rats after its contact with the fecal microflora of healthy rats.     

TcpA pilin sequences and colonization requirements for O1 and O139 Vibrio cholerae

The distribution, characterization and function of the tcpA gene was investigated in Vibrio cholerae O1 strains of the El Tor biotype and in a newly emergent non-O1 strain classified as serogroup O139. The V. cholerae tcpA gene from the classical biotype strain O395 was used as a probe to identify a clone carrying the tcpA gene from the El Tor biotype strain E7946. The sequence of the E7946 tcpA gene revealed that the mature El Tor TcpA pilin has the same number of residues as, and is 82% identical to, TcpA of classical biotype strain O395. The majority of differences in primary structure are either conservative or clustered in a manner such that compensatory changes retain regional amino acid size, polarity and charge. In a functional analysis, the cloned gene was used to construct an El Tor mutant strain containing an insertion in tcpA. This strain exhibited a colonization defect in the infant mouse cholera model similar in magnitude to that previously described for classical biotype tcpA mutants, thus establishing an equivalent role for TCP in intestinal colonization by El Tor biotype strains. The tcpA analysis was further extended to both a prototype El Tor strain from the Peru epidemic and to the first non-O1 strain known to cause epidemic cholera, an O139 V. cholerae isolate from the current widespread Asian epidemic. These strains were shown to carry tcpA with a sequence identical to E7946. These results provide further evidence that the newly emergent non-O1 serogroup O139 strain represents a derivative of an El Tor biotype strain and, despite its different LPS structure, shares common TCP-associated antigens. Therefore, there appear to be only two related sequences associated with TCP pilin required for colonization by all strains responsible for epidemic cholera, one primary sequence associated with classical strains and one for El Tor strains and the recent O139 derivative. A diagnostic correlation between the presence of tcpA and the V. cholerae to colonize and cause clinical is now extended to strains of both O1 and non-O1 serotypes.     

The comparative characteristics of Vibrio cholerae hemolysins]

Biochemical and biological properties of in vivo and in vitro hemolysins of cholera germs isolated by different authors as well as hemolysins of Vibrio parahaemolyticus and Escherichia coli have been comparatively characterized. According to the above data hemolysin of cholera germ El Tor is a thermolabile protein with molecular mass of 60-80 thou.; it is cytotoxic, enteropathogenic and lyses all the species of erythrocytes. Hemolysins of V. eltor and germs are immunologically related. Hemolysin of the cholera germ is thermostable and has molecular mass of 20-40 thou., that makes it similar to hemolysin of V. parahaemolyticus.     

Purification of El Tor cholera enterotoxins and comparisons with classical toxin.

In 55 clinical isolates of Vibrio cholerae biotype El Tor, cholera toxin (CT) production was higher after growth in liquid medium first under relatively anaerobic conditions followed by excessive aeration (AKI conditions) as compared with growth under the optimal conditions for CT production from V. cholerae of classical biotype (median toxin level being 400 ng ml-1 and 1 ng ml-1 respectively, for the two different growth conditions). Large growth volumes further enhanced El Tor toxin production to levels at or above 3-5 micrograms ml-1 from several strains, which allowed for easy purification of toxin by salt precipitation, aluminium hydroxide adsorption and/or GM1 ganglioside affinity chromatography. However, such purified El Tor CT completely lacked the A subunit when examined by SDS-PAGE or by monoclonal anti-A subunit antibody GM1-ELISA. In contrast, when El Tor CT was prepared from bacteria grown in the presence of specific antiserum against soluble haemagglutinin/protease it contained the A subunit (unnicked) in the same proportion to the B subunit (1A:5B) as classical CT. Immunodiffusion-in-gel tests revealed that the B subunits of El Tor and classical CTs share major epitopes but also have one or more weaker biotype-specific epitopes. The two types of toxin were practically indistinguishable in various GM1-ELISA tests, and antisera raised against El Tor and classical CT, respectively, could also completely neutralize the heterologous as well as the homologous toxin activity in vivo. The results indicate that CTs from El Tor and classical V. cholerae, despite demonstrable epitope differences, are predominantly cross-reactive and give rise to antisera with strong cross-neutralizing activity.     

Genotypic and PFGE/MLVA analyses of Vibrio cholerae O1: geographical spread and temporal changes during the 2007-2010 cholera outbreaks in Thailand

Background

Vibrio cholerae O1 El Tor dominated the seventh cholera pandemic which occurred in the 1960s. For two decades, variants of V. cholerae O1 El Tor that produce classical cholera toxin have emerged and spread globally, replacing the prototypic El Tor biotype. This study aims to characterize V. cholerae O1 isolates from outbreaks in Thailand with special reference to genotypic variations over time.

Methods/Findings

A total of 343 isolates of V. cholerae O1 from cholera outbreaks from 2007 to 2010 were investigated, and 99.4% were found to carry the classical cholera toxin B subunit (ctxB) and El Tor rstR genes. Pulsed-field gel electrophoresis (PFGE) differentiated the isolates into 10 distinct pulsotypes, clustered into two major groups, A and B, with an overall similarity of 88%. Ribotyping, multiple-locus variable-number tandem-repeat analysis (MLVA), and PCR to detect Vibrio seventh pandemic island II (VSP-II) related genes of randomly selected isolates from each pulsotype corresponded to the results obtained by PFGE. Epidemiological investigations revealed that MLVA type 2 was strongly associated with a cholera outbreak in northeastern Thailand in 2007, while MLVA type 7 dominated the outbreaks of the southern Gulf areas in 2009 and MLVA type 4 dominated the outbreaks of the central Gulf areas during 2009–2010. Only MLVA type 16 isolates were found in a Thai-Myanmar border area in 2010, whereas those of MLVA types 26, 39, and 41 predominated this border area in 2008. Type 39 then disappeared 1–2 years later as MLVA type 41 became prevalent. Type 41 was also found to infect an outbreak area.

Conclusions

MLVA provided a high-throughput genetic typing tool for understanding the in-depth epidemiology of cholera outbreaks. Our epidemiological surveys suggest that some clones of V. cholerae O1 with similar but distinctive genetic traits circulate in outbreak sites, while others disappear over time.     

Genetic diversity of toxigenic and nontoxigenic Vibrio cholerae serogroups O1 and O139 revealed by array-based comparative genomic hybridization

Toxigenic serogroups O1 and O139 of Vibrio cholerae may cause cholera epidemics or pandemics. Nontoxigenic strains within these serogroups also exist in the environment, and also some may cause sporadic cases of disease. Herein, we investigate the genomic diversity among toxigenic and nontoxigenic O1 and O139 strains by comparative genomic microarray hybridization with the genome of El Tor strain N16961 as a base. Conservation of the toxigenic O1 El Tor and O139 strains is found as previously reported, whereas accumulation of genome changes was documented in toxigenic El Tor strains isolated within the 40 years of the seventh pandemic. High phylogenetic diversity in nontoxigenic O1 and O139 strains is observed, and most of the genes absent from nontoxigenic strains are clustered together in the N16961 genome. By comparing these toxigenic and nontoxigenic strains, we observed that the small chromosome of V. cholerae is quite conservative and stable, outside of the superintegron region. In contrast to the general stability of the genome, the superintegron demonstrates pronounced divergence among toxigenic and nontoxigenic strains. Additionally, sequence variation in virulence-related genes is found in nontoxigenic El Tor strains, and we speculate that these intermediate strains may have pathogenic potential should they acquire CTX prophage alleles and other gene clusters. This genome-wide comparison of toxigenic and nontoxigenic V. cholerae strains may promote understanding of clonal differentiation of V. cholerae and contribute to an understanding of the origins and clonal selection of epidemic strains.     

Long-term survival of E1 Tor cholera vibrios in naturally contaminated sewage]

El Tor cholera vibrios of Ogava serological type were revealed in the sewage of the locomotive shed for 15 months. In experiment with an oil catcher in naturally infected sewage El Tor vibrios survived 36 days, in storage of this sewage at the laboratory--39 days, in the artificially infected sewage of a settlement and of a milk plant--2 and 11 days, respectively, in the oil and disel fuel--14 months. Consequently, El Tor vibrio can survive in the sewage with a high oil product content for a long time.     

Antimicrobial susceptibility and molecular characterization of <Emphasis Type="Italic">Vibrio cholerae</Emphasis> from cholera outbreaks in Chennai

The genotype and antibiotic resistance pattern of the toxigenic Vibrio cholerae strains associated with cholera outbreaks vary frequently. Fifty-one V. cholerae strains isolated from cholera outbreaks in Chennai (2002–2005) were screened for the presence of virulence and regulatory genes by multiplex polymerase chain reaction (PCR) assay. Genotyping of the isolates was done by VC1 primers derived from enterobacterial repetitive intergenic consensus (ERIC)-related sequence in V. cholerae. All the isolates possessed toxigenic genes, such as ctxA, ctxB, tcpA, ace, ompU, toxR and zot. Two different El Tor genotypes and one O139 genotype could be delineated by VC1-PCR. One of the El Tor genotypes was similar to the El Tor strains isolated from Bhind district and Delhi during 2004. Antibiotic susceptibility testing revealed greater variability among the isolates tested. All the isolates were found to be susceptible to norfloxacin, ciprofloxacin and tetracycline. Thiry-three per cent of the isolates were found to be resistant to more than 4 antibiotics and could be termed as multiple antibiotic resistant. Coexistence of O139 serogroup along with the El Tor biotype could be identified among the strains recovered during the period 2002–2004. The O139 isolates were found to be more susceptible to the antibiotics tested when compared to the El Tor isolates.     

Biotype-specific tcpA genes in Vibrio cholerae

Abstract The tcpA gene, encoding the structural subunit of the toxin-coregulated pilus, has been isolated from a variety of clinical isolates of Vibrio cholerae , and the nucleotide sequence determined. Strict biotype-specific conservation within both the coding and putative regulatory regions was observed, with important differences between the El Tor and classical biotypes. V. cholerae O139 Bengal strains appear to have El Tor-type tcpA genes. Environmental O1 and non-O1 isolates have sequences that bind an E1 Tor-specific tcpA DNA probe and that are weakly and variably amplified by tcpA -specific polymerase chain reaction primers, under conditions of reduced stringency. The data presented allow the selection of primer pairs to help distinguish between clinical and environmental isolates, and to distinguish El Tor (and Bengal) biotypes from classical biotypes from classical biotypes of V. cholerae . While the role of TcpA in cholera vaccine preparations remains unclear, the data strongly suggest that TcpA-containing vaccines directed at O1 strains need include only the two forms of TcpA, and that such vaccines directed at (O139) Bengal strains should include the TcpA of El Tor biotype.     

Role of neuraminidase from cholera vibrions in the pathogenesis of experimental cholera]

A study was made of a possible effect of neuraminidase of cholera vibrios on cholera pathogenesis. It was shown that in intraintestinal injection of cholera vibrios of the El Tor biotype to nursling rabbits neuraminidase could be revealed in their intestine 5 to 8 hours after the infection. Addition of neuraminidase to the weakly cholerogenic strain cholera vibrios intensified its cholerogenic action in infection of the animals. The antineuraminidase serum administered to the infected rabbits prevented clinical manifestations of experimental cholera, although it failed to always eliminate the cholerogenic syndrome (revealed during autopsy). At the same time neuraminidase did not influence the capacity of cholerogen to produce the cholerogenic syndrome. The authors consider that the action of the enzyme should occur at the early stages of the pathogenic process, and could be associated with creation of conditions for the attachement of cholera causative agent to the intestinal wall or for the action of their exotoxin.