Prevalence of Vibrio cholerae O1 El Tor variant in a cholera-endemic zone of Kenya
Suleiman M. SaidiNityananda ChowdhurySharda Prasad AwasthiMasahiro AsakuraAtsushi HinenoyaYoshio IijimaShinji Yamasaki
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Since 2007, Kenya has experienced an increase in cholera outbreaks characterized by a high fatality rate. In this study, we characterized 81 Vibrio cholerae isolates from diarrhoeal stool samples in Nyanza, a cholera-endemic lake region of Kenya, for virulence properties, clonality and antibiotic susceptibility. Eighty of these isolates were V. cholerae O1 El Tor variants carrying the classical ctxB gene sequence, while one isolate was V. cholerae non-O1/O139. All of the El Tor variants were of clonal origin, as revealed by PFGE, and were susceptible to ampicillin, tetracycline, ciprofloxacin, fosfomycin, kanamycin and norfloxacin. However, the isolates showed resistance to sulfamethoxazole/trimethoprim and streptomycin, and intermediate resistance to nalidixic acid, chloramphenicol and imipenem. The non-O1/O139 isolate carried the cholix toxin II gene (chxA II) and was susceptible to all antimicrobials tested except ampicillin. We propose that an El Tor variant clone caused the Nyanza cholera outbreak of 2007-2008.Keywords:
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We examined clinical samples from Nigerian patients with acute watery diarrhea for Vibrio cholerae during the 2010 cholera outbreak. A total of 109 suspected isolates were characterized, but only 57 V. cholerae strains could be confirmed using multiplex real-time PCR as well as rpoB sequencing and typed as V. cholerae O:1 Ogawa biotype El Tor. This finding highlighted the need for accurate diagnosis of cholera in epidemic countries to implement life-saving interventions.
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The millions of deaths from cholera during the past 200 y, coupled with the morbidity and mortality of cholera in Haiti since October 2010, are grim reminders that Vibrio cholerae , the etiologic agent of cholera, remains a scourge. We report the isolation of both V . cholerae O1 and non-O1/O139 early in the Haiti cholera epidemic from samples collected from victims in 18 towns across eight Arrondissements of Haiti. The results showed two distinct populations of V. cholerae coexisted in Haiti early in the epidemic. As non-O1/O139 V . cholerae was the sole pathogen isolated from 21% of the clinical specimens, its role in this epidemic, either alone or in concert with V . cholerae O1, cannot be dismissed. A genomic approach was used to examine similarities and differences among the Haitian V . cholerae O1 and V . cholerae non-O1/O139 strains. A total of 47 V . cholerae O1 and 29 V . cholerae non-O1/O139 isolates from patients and the environment were sequenced. Comparative genome analyses of the 76 genomes and eight reference strains of V . cholerae isolated in concurrent epidemics outside Haiti and 27 V . cholerae genomes available in the public database demonstrated substantial diversity of V. cholerae and ongoing flux within its genome.
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Vibrio cholerae O1 biotype El Tor (ET), the cause of the current 7th pandemic, has recently been replaced in Asia and Africa by an altered ET biotype possessing cholera toxin (CTX) of the classical (CL) biotype that originally caused the first six pandemics before becoming extinct in the 1980s. Until recently, the ET prototype was the biotype circulating in Peru; a detailed understanding of the evolutionary trend of V. cholerae causing endemic cholera in Latin America is lacking. The present retrospective microbiological, molecular, and phylogenetic study of V. cholerae isolates recovered in Mexico (n = 91; 1983 to 1997) shows the existence of the pre-1991 CL biotype and the ET and CL biotypes together with the altered ET biotype in both epidemic and endemic cholera between 1991 and 1997. According to sero- and biotyping data, the altered ET, which has shown predominance in Mexico since 1991, emerged locally from ET and CL progenitors that were found coexisting until 1997. In Latin America, ET and CL variants shared a variable number of phenotypic markers, while the altered ET strains had genes encoding the CL CTX (CTX(CL)) prophage, ctxB(CL) and rstR(CL), in addition to resident rstR(ET), as the underlying regional signature. The distinct regional fingerprints for ET in Mexico and Peru and their divergence from ET in Asia and Africa, as confirmed by subclustering patterns in a pulsed-field gel electrophoresis (NotI)-based dendrogram, suggest that the Mexico epidemic in 1991 may have been a local event and not an extension of the epidemics occurring in Asia and South America. Finally, the CL biotype reservoir in Mexico is unprecedented and must have contributed to the changing epidemiology of global cholera in ways that need to be understood.
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ABSTRACT We determined the types of cholera toxin (CT) produced by a collection of 185 Vibrio cholerae O1 strains isolated in Bangladesh over the past 45 years. All of the El Tor strains of V. cholerae O1 isolated since 2001 produced CT of the classical biotype, while those isolated before 2001 produced CT of the El Tor biotype.
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ABSTRACT Vibrio cholerae O1 El Tor variant strains produced much more cholera toxin than did prototype El Tor strains. The amount of cholera toxin produced by El Tor variant strains both in vitro and in vivo was more or less equivalent to that produced by classical strains.
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Soon after its entry into the Indo-Pakistan subcontinent in 1964, cholera El Tor progressively replaced classical cholera. One of the probable reasons for this was found from laboratory studies of the interaction of the two choleragenic vibrios, V. cholerae and V. El Tor. It was observed, in both in vitro and in vivo experiments, that in mixed culture El Tor vibrios from cholera cases are capable of outgrowing and rapidly eliminating V. cholerae. The apathogenic El Tor strains from the Middle East countries differed significantly from the pathogenic type of El Tor strains isolated from cholera cases in that the former did not inhibit the growth of V. cholerae strains. The possible mechanism of interaction of the pathogenic El Tor vibrios and V. cholerae was studied in detail. Various possibilities, including higher rates of multiplication of El Tor vibrios, competition for nutrients, secretion of inhibitory substances and liberation of lethal bacteriophage or vibriocins by El Tor vibrios, were examined. Although it was not possible to establish the actual mechanism of this interaction, the possible biological effect on the epidemiology of cholera was evident.
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Vibrio cholerae O139 is a recently identified non-O1 V. cholerae strain responsible for outbreaks of epidemic cholera in India, Bangladesh, and Thailand in the past 2 years. Other workers have demonstrated the presence of the cholera toxin genetic element in V. cholerae O139, unlike the situation for other non-O1 V. cholerae strains. We sought to compare further this strain with strains of V. cholerae O1, classical and El Tor biotypes, by classic microbiologic methods, Southern blot analysis for restriction fragment length polymorphisms with probes for iron-regulated genes of V. cholerae O1, and comparisons of outer membrane protein profiles. Our results were similar for V. cholerae O139 and the El Tor biotype of V. cholerae O1, with the exception of the constitutive expression in V. cholerae O139 of OmpS, an outer membrane protein that was maltose inducible in comparison strains of V. cholerae O1.
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In October 1992, a new strain of cholera, subsequently designated Vibrio cholerae O139 Bengal, was detected in Madras, India. This strain spread rapidly through the Indian subcontinent and has now been reported in many parts of Asia, with additional cases identified in travelers to North American and the Middle East. Phylogenetically, V. cholerae O139 Bengal is very closely related to "standard" V. cholerae O1 El Tor strains; it produces cholera toxin and causes an illness identical that seen with V. cholerae O1. However, prior immunity to V. cholerae O1 El Tor does not appear to protect against illness caused by V. cholerae O139 Bengal. O139 Bengal strains have a short, "semi-rough" O side chain and are encapsulated, changes that are likely to have accounted for their ability to cause disease in persons with prior exposure to cholera. These changes in surface structures appear to have resulted from a limited number of genetic modifications. The appearance of V. cholerae O139 Bengal may well herald the beginning of the eighth pandemic of cholera--and underscores the tremendous potential within nature for creation of new strains of "old" pathogens.
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The review deals with the properties of Vibrio cholerae (classical, El Tor, 0139, non-01/non-0139 strains) circulating worldwide during the seventh cholera pandemic. Particular attention is given to the variability in the cholera pathogen: the replacement of classical Vibrio cholerae by the El Tor biotype and subsequently the emergence of serogroup Vibrio cholerae 0139 and genetically altered El Tor Vibrio cholerae; the causes giving rise to these changes and spread of Vibrio cholera in the countries of the Asian continent. A large genetic variability found in Asian strains suggests that there is a real possibility of the emergence of new clones with new properties, including those with an epidemic potential. The Vibrio cholerae strains, that periodically appear in Asia and have an epidemic potential and new properties, spread over all continents, by causing cholera infection. The cholera pathogen adapts to new existence conditions in some cases, by altering some properties and, by having been rooted in a certain area, causes mainly sporadic cases of the disease. These Vibrio cholerae strains, unlike the Asian strains (the pathogens of the seventh pandemic), may be virulent, by preserving the virulence genes in the genome; however, they are, in most cases, non-endemic and unable to spread widely.
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