Cholera Due to Altered El Tor Strains of Vibrio cholerae O1 in Bangladesh

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.Vibrio cholerae O1 has two biotypes, namely, classical and El Tor, which are believed to have evolved from separate lineages (7,8), and these biotypes have traditionally been differentiated by a number of phenotypic traits. Comparative genomic analyses have recently revealed a high degree of conservation among diverse strains of V. cholerae but have also shown genes that differentiate the classical biotype from the El Tor biotype (3). Apart from these phenotypic and genetic differences, there are also dissimilarities in the infection patterns of disease caused by the two biotypes. These include the occurrence of more asymptomatic than symptomatic carriers of El Tor strains, who outnumber active patients by a ratio of up to 50:1 (14), better survival of El Tor strains in the environment and in the human host, and more efficient host-to-host transmission of El Tor strains than of classical strains (5). There is firm evidence that the fifth and sixth pandemics of cholera were caused by the classical biotype, while the ongoing seventh pandemic is caused by the El Tor biotype, which has now globally replaced the classical biotype.Cholera toxin (CT), the principal toxin produced by V. cholerae O1 and O139, is responsible for most of the manifestations of the disease cholera. Based on the B subunit of CT, two immunologically related but not identical epitypes have been described: CT1 is the prototype elaborated by classical biotype strains and by U.S. Gulf Coast strains, while CT2 is produced by the El Tor biotype and O139 strains (4). Another classification identifies three types of ctxB genes based on three nonrandom base changes resulting in changes in the deduced amino acid sequence. Genotype 1 is found in strains of the classical biotype worldwide and in U.S. Gulf Coast strains, genotype 2 is found in El Tor biotype strains from Australia, and genotype 3 is found in El Tor biotype strains from the seventh pandemic and the Latin American epidemic (12). Thus, the V. cholerae O1 El Tor biotype of the ongoing seventh pandemic produces CT of the CT2 epitype and genotype 3, while the classical biotype CT belongs to the CT1 epitype and genotype 1. In this study, we examined a collection of clinical V. cholerae O1 strains isolated in Bangladesh during the past four and a half decades, using monoclonal antibodies (MAbs) produced to classical and El Tor CTs, and found that V. cholerae O1 El Tor strains isolated since 2001 in Bangladesh produce the CT subtype of the classical biotype.One hundred eighty-five strains of V. cholerae O1, consisting of 31 strains of the classical biotype isolated between 1960 and 1990 and 113 strains of the El Tor biotype and 41 hybrid strains of V. cholerae O1 (strains that could ...

Isolation, characterization and mode of antimicrobial action againstVibrio choleraeof methyl gallate isolated fromAcacia farnesiana

“…The main virulence factors of V. cholerae are cholera toxin (CT) and toxin coregulated pili (TCP), which are encoded by the genes ctxAB and tcpA, respectively (Nair et al 2006). In this work, no effect of methyl gallate on the expression of the enterotoxin gene (ctxAB) was detected, which undoubtedly indicates that the inhibitory activity reported is mainly due to its effect on the membrane of V. cholerae.…”

A large cholera outbreak due to a new cholera toxin variant of the Vibrio cholerae O1 El Tor biotype in Orissa, Eastern India

“…Previously, changes in the amino acid sequence of El Tor strains at positions 39 and 69 have been reported and these sequences were similar to those of classical strains (Ansaruzzaman et al, 2004). Subsequently, these El Tor strains producing classical CT were isolated from many parts of various Asian countries (Nair et al, 2006 relationships. ERIC-PCR with genomic DNA of various V. cholerae strains resulted in amplification of multiple fragments of DNA with sizes ranging from 0.6 to 1.8 kb (Fig.…”

“…There are certain structural and functional peculiarities in the pathogenicity genes of El Tor vibrios that make the symptoms of cholera milder but longer lasting than the symptoms of the classical biotype strains (Smirnova et al, 2004). However, in the recent past, evolution among El Tor strains by the emergence of hybrid biotype strains with altered cholera toxin (CT) has been noticed (Nair et al, 2006). Although several toxins have been reported from V. cholerae, CT is still the major one responsible for most of the manifestations of cholera (Kaper et al, 1995).…”

Genetic characteristics of drug-resistant Vibrio cholerae O1 causing endemic cholera in Dhaka, 2006–2011

“…Genotypes 1, 2, 3, 7, 10 and 11 were found in serogroup O1 strains, genotypes 3, 4, 5 and 6 were found in serogroup O139 strains, and genotypes 8 and 9 were found only in serogroups O27 and O37, respectively (Marin & Vicente, 2012). A significant and recent incident in the history of cholera has been the emergence of V. cholerae altered ET, which has the ctxB gene of V. cholerae CL biotype , and which has been recognized as a new pandemic pathogen with the capacity to spread globally (Chin et al, 2011;Nair et al, 2002Nair et al, , 2006, causing more severe disease (Siddique et al, 2010). According to a recent study, a new ctxB variant of V. cholerae with an amino acid substitution at position 20 [histidine (H)Aasparagine (N)], designated genotype 7, was found to be associated with a large cholera outbreak in India (Kumar et al, 2009).…”