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Emergence of Tetracycline-Resistant Vibrio cholerae O1 Amit Roychowdhury, Arpita Pan, Dharitri Dutta, Asish Kumar Mukhopadhyay, T. Ramamurthy, Ranjan Kumar Nandy, Sujit Kumar Bhattacharya and Mihir Kumar Bhattacharya* National Institute of Cholera and Enteric Diseases, Kolkata, India (Received March 16, 2007. Accepted December 3, 2007) SUMMARY: Out of 2,235 diarrheal stool samples collected from patients admitted to the Infectious Diseases
Hospital, Kolkata, 343 cases were positive for Vibrio cholerae (341, V. cholerae O1 and 2, O139). During the
year 2004, infections caused by V. cholerae serotype Ogawa and Inaba were 93 and 7%, respectively, while in
2005, the Inaba isolation rate rose to 88% as compared to 12% for Ogawa. Susceptibility to antimicrobial agents
revealed that the O1 strains were resistant to multiple antibiotics (ampicillin, co-trimoxazole, furazolidone,
nalidixic acid and streptomycin) with reduced susceptibility to ciprofloxacin. Increased isolation of tetracycline-
resistant strains (27.3% for Ogawa and 15% for Inaba) was noted in 2005. It appears that the population might be
at risk of infection by the Inaba serotype and that tetracycline may not be useful for the treatment.
The disease known as ‘cholera’ is characterized by the pas- ATCC strains Escherichia coli 25922 were used as a stand- sage of voluminous watery stools, which rapidly leads to dehydration and if left untreated, may cause death. The Screening of 2,235 specimens collected from hospitalized toxigenic Vibrio cholerae strains belonging to O1 and O139 diarrheal patients resulted in detection of a total of 343 chol- serogroups are the causative agents of cholera. V. cholerae era cases during 2004 - 2005. Out of 343 cases, 341 cases were strains belonging to the O1 serogroup are further classified caused by V. cholerae O1 and 2 by the O139 serogroup.
into two biotypes, Classical and El Tor, and into two major Serotyping analysis showed that 104 cases (30.5%) belonged serotypes--Inaba and Ogawa. During the last decade, the to Inaba and 237 cases (69.5%) to Ogawa serotypes. Cholera dominance of Ogawa belonging to the O1 serotype with a due to O1 infection was found among 241 and 100 cases quiescent period during the O139 era was observed (1). We during 2004 and 2005, respectively. Among the 241 cases have witnessed the reemergence of V. cholerae O1 strains of during 2004, 224 (93%) were by Ogawa and 17 (7%) by El Tor biotype, serotype Inaba, among the cholera patients Inaba. While 93% (n = 241) cases were by Ogawa in 2004, admitted to the Infectious Diseases Hospital (IDH), Kolkata a dramatic drop to 12% (n = 100) Ogawa cases was observed since August 2004 (2). V. cholerae O1 strains can undergo in 2005. Conversely, infections due to Inaba strains increased shifting between the Ogawa and Inaba serotypes during sharply in 2005 and reached 88% (n = 100) as compared to epidemics or in areas where cholera is endemic (3). Cycles 7% (n = 241) cases in 2004. After almost 16 years of quies- of serotype shifting extending between 2 and 8 years have cence since 1989, a preponderance of the Inaba serotype already been reported (4). The detection in clinical cases of among cholera cases was observed in 2005. Detection of V.
V. cholerae that shows resistance to multiple drugs in- cholerae O139 from cholera cases was less significant. This cluding co-trimoxazole, nalidixic acid, furazolidone and trend started in 2003 and has continued up to the writing of fluoroquinolones, has complicated the situation (5,6). The this report. A declining trend in the isolation of V. cholerae present study was conducted to track and portray the nature O139 cases from 2003 possibly created a consonance for the of the newly emerged V. cholerae O1 Inaba strains, in Kolkata, Inaba serotype to reemerge. Incidence of V. cholerae O1 Inaba in different parts of India have been reported recently (2,8).
Stool samples or rectal swabs collected from patients Both the Inaba and Ogawa strains displayed similar re- enrolled in the surveillance system established at IDH, sistance profiles when tested for their susceptibility to Kolkata, were processed for the isolation and identification different antimicrobial agents including quinolones and of Vibrio spp. through initial plating on thiosulfate citrate bile fluoroquinolones. As shown in Table 1, most of the strains salt (TCBS) agar followed by biochemical analysis of the were resistant to ampicillin, co-trimoxazole, furazolidone, sucrose-fermenting yellow-colored colonies. The V. cholerae nalidixic acid and streptomycin and exhibited reduced strains were serotyped based on their agglutinibility with susceptibility to ciprofloxacin (reduced susceptibility of 90.7 monospecific antisera to O1 and O139. The O1 strains were and 0.0% for Ogawa and 90.0 and 20.0% for Inaba strains further classified into Ogawa or Inaba serotypes.
isolated during 2004 and 2005, respectively). Importantly, Susceptibility to different antimicrobial agents was carried isolation of tetracycline-resistant strains, 27.3 and 15% for out by the disc diffusion technique (7), and commercially Ogawa and Inaba, respectively, were noted in 2005. The V.
available discs (HiMedia, Mumbai, India) were used. The cholerae O1 strains interconvert between the Ogawa andInaba serotypes, and the mechanism for multidrug resistance *Corresponding author: Mailing address: National Institute of appears to be same for both serotypes.
Cholera and Enteric Diseases, P33 CIT Road, Scheme XM, The switching over of Ogawa to serotype Inaba as well as Beliaghata, Kolkata, India 700010. Tel: +91-33-2370-1176, Fax: its acquisition of resistance to tetracycline should serve as a +91-33-2370-5066, E-mail: mkbidh@gmail.com warning of possible future cholera outbreaks by multidrug Table 1. Susceptibility of V. cholerae O1 strains to different Percentage resistance of V. cholerae O1 REFERENCES
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ACKNOWLEDGMENTS
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of Health, Labor and Welfare of Japan (Project H17-Shinkou-3), and was also supported in part by the Japan International Cooperation Agency (JICA/

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