Genetic determinants of virulence, antibiogram and altered biotype among the Vibrio cholerae O1 isolates from different cholera outbreaks in India A.K. Goel a,b , S.C. Jiang b, * a Biotechnology Division, Defence Research & Development Establishment, Jhansi Road, Gwalior 474002, India b Department of Civil and Environmental Engineering, University of California, Irvine 92697, USA 1. Introduction Cholera is one of the most potent diarrheal diseases that continue to ravage many developing countries. This is one disease in modern time that is endemic, epidemic and pandemic in nature. Infections due to Vibrio cholerae have been reported from all over the world, although they are of primary importance in developing countries where endemic cholera remains a serious health threat and are particularly associated with poverty and poor sanitation (Lee, 2001). In 2007, WHO recorded a total of 177,963 cases including 4031 deaths, generating a case fatality rate of 2.3% (WHO, 2008). This represents a 25% decrease in the number of officially notified cases compared with 2006, but an increase of 46% in the mean number of cases reported during 2002–2005. These annual figures of WHO actually represent the tip of the iceberg, because the morbidity and mortality caused by V. cholerae is grossly underreported owing to surveillance difficulties and also for fear of economic and social consequences. Two distinctive epidemiological features of cholera are its tendency to appear in explosive outbreaks, often starting in several distinct foci simultaneously, and its propensity to cause true epidemics that progressively affect many countries in multiple continents over the course of many years (Kaper et al., 1995). The disease is manifested by profuse watery diarrhea, vomiting and dehydration, often associated with leg cramps due to electrolyte imbalance leading to severe dehydration and death. Generally, cholera is associated with poverty, malnutrition and overpopulation. World has already faced seven cholera pandemics in the past two centuries (Kaper et al., 1995). The traditional home of cholera is the Ganga delta of India and Bangladesh. However, it has been spread to many other countries over three continents. There are two biotypes of V. cholerae O1 strain, classical and El Tor which are believed to have evolved from separate lineages (Kaper et al., 1995). Among the two biotypes, El Tor strains have better adaptability to survive in the environment and in the human host as they colonize better in the intestinal epithelium (Finkelstein, 2006). Strains of classical biotype are suggested to be more toxigenic than El Tor strains (Huq et al., 1993). The ongoing 7th pandemic was caused by V. cholerae O1 El Tor that started from Indonesia in 1961 (Faruque et al., 1998). After 2001, hybrid strains Infection, Genetics and Evolution 10 (2010) 815–819 ARTICLE INFO Article history: Received 28 April 2009 Received in revised form 22 June 2009 Accepted 26 June 2009 Available online 4 July 2009 Keywords: Vibrio cholerae Cholera Pathogenicity Toxin Antibiotic resistant Evolution Biotype ABSTRACT Cholera diarrhea is still a major health challenge for a large part of globe. Global replacement of Vibrio cholerae classical biotype by El Tor biotype, emergence of O139 serogroup and rapid spread of antibiotic resistant strains indicate the continuous evolution in V. cholerae. In this study, 114 V. cholerae O1 serotype Ogawa isolates, collected from different cholera outbreaks in different regions of India between 2004 and 2007 were subjected to biochemical, immunological and molecular characterization. All the isolates were PCR positive for various toxigenic, pathogenic and regulatory genes, viz. ompW, ctxB, rfbO1, tcp, zot, rtxC, ace, hlyA, ompU and toxR. The antibiogram studies of isolates revealed the resistance towards several antibiotics including nalidixic acid, co-trimoxazole, streptomycin, nitrofurantoin and polymyxin B. However, antibiogram of the strains confirmed susceptibility to tetracycline and chloramphenicol in all the isolates. This study also substantiated the wide spread of class 1 integrons and SXT elements (mobile genetic elements for antibiotic resistance) in clinical isolates in India. Sequencing of cholera toxin (ctxB) gene revealed the replacement of traditional ctxB of El Tor biotype with ctxB of classical biotype in all the O1 El Tor strains collected since 2004. In addition, in 2007, a new variant of O1 El Tor strain with further modifications in ctxB of classical biotype is discovered among the Indian isolates. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +1 949 824 5527; fax: +1 949 824 2056. E-mail address: sjiang@uci.edu (S.C. Jiang). Contents lists available at ScienceDirect Infection, Genetics and Evolution journal homepage: www.elsevier.com/locate/meegid 1567-1348/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.meegid.2009.06.022