Occurrence of Antibiotic Resistance Gene Cassettes aac ( 6 ′) -Ib , dfrA5 , dfrA12 , and ereA2 in Class I Integrons in Non-O1, Non-O139 Vibrio cholerae Strains in India

Abstract

Molecular mechanisms of multidrug resistance in Vibrio cholerae belonging to non-O1, non-O139 serogroups isolated during 1997 to 1998 in Calcutta, India, were investigated. Out of the 94 strains examined, 22 strains were found to have class I integrons. The gene cassettes identified were dfrA1, dfrA15, dfrA5, and dfrA12 for trimethoprim; aac(6)-Ib for amikacin and tobramycin; aadA1 and aadA2 for streptomycin and spectinomycin; and ereA2 for erythromycin resistance. To our knowledge, this is the first report of the presence of dfrA5, dfrA12, aac(6)-Ib, and ereA2 cassettes in class I integrons of V. cholerae. Forty-three of 94 strains also had plasmids, and out of these, 14 contained both class I integrons and plasmids. Pulsed-field gel electrophoresis followed by Southern hybridization revealed that in the 14 plasmid-bearing strains, class I integrons resided either on chromosomes, on plasmids, or on both. Our results indicated that besides class I integrons and plasmids, a conjugative transposon element, SXT, possibly contributed to the multiple antibiotic resistance.Cholera is a serious epidemic disease caused by the gramnegative bacterium Vibrio cholerae. Only V. cholerae strains belonging to the O1 and O139 serogroups are thought to be capable of causing epidemic cholera. Strains belonging to serogroups other than O1 and O139, collectively referred to as non-O1, non-O139 strains, are ubiquitously found in the aquatic environs (19) and are also capable of causing sporadic diarrhea. In 1996, an inexplicable upsurge in the incidence of cholera strains belonging to serogroups other than O1 and O139 occurred in Calcutta, India. After extensive molecular characterization, these strains were found to be devoid of the ctx filamentous phage (CTX) (31) and some other virulence genes (27). Based on these findings, it was concluded that some strains of V. cholerae belonging to different serotypes can cause diarrhea clinically indistinguishable from that associated with cholera (5) by a mechanism that could be distinct from that employed by the toxigenic V. cholerae O1 and O139 strains. The nomenclature "enteropathogenic V. cholerae" (EPVC) was proposed to include these serotypes (27). The incidence of EPVC had shown an upward trend from 1997 that continued into 1998. In the months of July and August 1998, the EPVC strains constituted one-third of the V. cholerae strains isolated from hospitalized patients (12). Recently a comparative study of clinical and environmental isolates of non-O1, non-O139 V. cholerae strains belonging to matching serogroups from our laboratories revealed that, despite sharing the same serogroups, the environmental and clinical isolates were genetically heterogeneous and also that the resistance to multiple antibiotics was more common among the clinical isolates (5). Multiple-antibiotic-resistant isolates of non-O1, non-O139V. choelrae strains were identified in children with diarrhea in Bangkok, Thailand (7).Reports of drug-resistant V. cholerae strains are appearing with increasing frequency (2...

Emergence of Salmonella epidemics: The problems related to Salmonella enterica serotyp Enteritidis and multiple antibiotic resistance in other major serotypes

“…Another possibility is the exchange between aadA2 and the two gene cassettes which would imply excision, mediated by the integron-encoded integrase, of aadA2 and its replacement by the other gene cassettes [64]. The array of gene cassettes found at the first attI1 site of the S. Albany strain was interestingly the same as those recently reported in integrons from Vibrio cholerae isolated in Thailand and India [36,142].…”

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).…”

“…Using PCR assays, all antibiotic-resistant V. cholerae O1 strains were examined for the presence of the SXT element and class 1 integron. The detection of SXT and intI1 was performed using primers and procedures described elsewhere (Thungapathra et al, 2002).…”

“…Over the past few years, ET causing Asiatic cholera has shown remarkable changes in its phenotypic and genetic characteristics (Nair et al, 2002). Recent molecular analysis of ET strains causing acute watery diarrhoea in Bangladesh shows them to be hybrids because they possess phenotypic and genotypic traits of the CL biotype against an ET background (Nair et al, 2002).…”

“…Over the past few years, ET causing Asiatic cholera has shown remarkable changes in its phenotypic and genetic characteristics (Nair et al, 2002). Recent molecular analysis of ET strains causing acute watery diarrhoea in Bangladesh shows them to be hybrids because they possess phenotypic and genotypic traits of the CL biotype against an ET background (Nair et al, 2002). Subsequent retrospective studies showed that all of the O1 ET strains isolated in Bangladesh since 2001 were hybrids of both CL and ET biotypes, while those isolated before 2001 contained all the ET attributes of the seventh pandemic V. cholerae O1 .…”