Hybrid & El Tor variant biotypes of Vibrio cholerae O1 in Thailand
M Na-Ubol1, P Srimanote2, M Chongsa-nguan1, N Indrawattana1, N Sookrung3, P Tapchaisri2, S Yamazaki4, L Bodhidatta5, B Eampokalap6, H Kurazono7, H Hayashi8, GB Nair9, Y Takeda9, W Chaicumpa10
1 Department of Microbiology & Immunology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
2 Graduate Studies, Faculty of Allied Health Sciences, Thammasat University, Pathumthani, Thailand
3 Office for Research & Development, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
4 Department of Veterinary Science, Graduate School of Life & Environmental Sciences, Osaka Prefecture University, Osaka, Japan
5 Department of Enteric Diseases, Armed Force Research Institute of Medical Science, US Army Component, Bangkok, Thailand
6 Bamrasnaradura Institute, Nonthaburi, Thailand
7 Obihiro University of Agriculture & Veterinary Medicine, Department of Animal & Food Hygiene, Hokkaido, Japan
8 Department of Microbiology & Nutrition, Chugoku-gakuen University, Okayama, Japan
9 National Institute of Cholera & Enteric Diseases, Kolkata, India
10 Department of Parasitology & Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
Emeritus Professor, Department of Parasitology, Faculty of Medicine Siriraj Hospital Mahidol University, Bangkok 10700
Source of Support: None, Conflict of Interest: None
Background & objectives : El Tor Vibrio cholerae O1 carrying ctxB C trait, so-called El Tor variant that causes more severe symptoms than the prototype El Tor strain, first detected in Bangladesh was later shown to have emerged in India in 1992. Subsequently, similar V. cholerae strains were isolated in other countries in Asia and Africa. Thus, it was of interest to investigate the characteristics of V. cholerae O1 strains isolated chronologically (from 1986 to 2009) in Thailand.
Methods: A total of 330 V. cholerae O1 Thailand strains from hospitalized patients with cholera isolated during 1986 to 2009 were subjected to conventional biotyping i.e., susceptibility to polymyxin B, chicken erythrocyte agglutination (CCA) and Voges-Proskauer (VP) test. The presence of ctxA, ctxB, zot, ace, toxR, tcpA C , tcpA E, hlyA C and hlyA E were examined by PCR. Mismatch amplification mutation assay (MAMA) - and conventional- PCRs were used for differentiating ctxB and rstR alleles.
Results: All 330 strains carried the El Tor virulence gene signature. Among these, 266 strains were typical El Tor (resistant to 50 units of polymyxin B and positive for CCA and VP test) while 64 had mixed classical and El Tor phenotypes (hybrid biotype). Combined MAMA-PCR and the conventional biotyping methods revealed that 36 strains of 1986-1992 were either typical El Tor, hybrid, El Tor variant or unclassified biotype. The hybrid strains were present during 1986-2004. El Tor variant strains were found in 1992, the same year when the typical El Tor strains disappeared. All 294 strains of 1993-2009 carried ctxBC ; 237 were El Tor variant and 57 were hybrid.
Interpretation & conclusions : In Thailand, hybrid V. cholerae O1 (mixed biotypes), was found since 1986. Circulating strains, however, are predominantly El Tor variant (El Tor biotype with ctxB C).