RESEARCH understanding of factors that contribute to the emergence of new pathogenic strains. This work was supported in part by an American Society for Microbiology travel fellowship to Dr. Garg. Dr. Garg completed this work as part of her Ph.D. disserta- tion at University of Calcutta. She is a postdoctoral fellow at the University of Maryland School of Medicine, pursuing studies of thrombospondin in human microvascular endothelial cells. References 1. Bhattacharya SK, Bhattacharya MK, Nair GB, Dutta D, Deb A, Ramamurthy T, et al. Clinical profile of acute diarrhoea cases infect- ed with the new epidemic strain of Vibrio cholerae O139: designation of the disease as cholera. J Infect 1993;27:11–8. 2. Nair GB, Ramamurthy SK, Mukhopadhyay T, Garg S, Bhattacharya MK, Takeda T, et al. Spread of Vibrio cholerae O139 Bengal in India. J Infect Dis 1994;169:1029–34. 3. Comstock LE, Johnson JA, Michalski JM, Morris JG, Kaper JB. Cloning and sequence of a region encoding surface polysaccharide of Vibrio cholerae O139 and characterization of the insertion site in the chromosome of Vibrio cholerae O1. Mol Microbiol 1966;19:815–26. 4. Stroeher UH, Parasivam G, Dredge BK, Manning PA. Novel Vibrio cholerae O139 genes involved in lipopolysaccharide biosynthesis. J Bacteriol 1997;179:2740–7. 5. Bik EM, Bunschoten AE, Willems RJL, Chang ACY, Mooi FR. Genetic organization and functional analysis of the otn DNA essen- tial for cell-wall polysaccharide synthesis in Vibrio cholerae O139. Mol Microbiol 1996;20:799–811. 6. Basu A, Garg P, Datta S, Chakraborty S, Bhattacharya T, Yamasaki S, et al. Vibrio cholerae O139 in Calcutta, 1992–1998: incidence, antibi- ograms, and genotypes. Emerg Infect Dis 2000;6:139–47. 7. Faruque SM, Saha MN, Asadulghani, Bag PK, Bhadra RK, Bhattacharya SK, et al. Genomic diversity among Vibrio cholerae O139 strains isolated in Bangladesh and India between 1992 and 1998. FEMS Microbiol Lett 2000;184:279–84. 8. Stine OC, Sozhamannan S, Gou Q, Zheng S, Morris JG, Johnson JA. Phylogeny of Vibrio cholerae based on recA sequence. Infect Immun 2000;68:7180–5. 9. Garg P, Chakraborty S, Basu I, Datta S, Rajendran K, Bhattacharya T, et al. Expanding multiple antibiotic resistance among clinical strains of Vibrio cholerae isolated from 1992–7 in Calcutta, India. Epidemiol Infect 2000;124:393–9. 10. Kurazono H, Yamasaki S, Ratchtrachenchai O, Nair GB, Takeda Y. Analysis of Vibrio cholerae O139 Bengal isolated from different geo- graphical areas using macrorestriction DNA analysis. Microbiol Immunol 1996;40:303–5. 11. Maiden MCJ, Bygraves JA, Feil E, Morelli G, Russell JE, Urwin R, et al. Multilocus sequence typing: a portable approach to the identifi- cation of clones within populations of pathogenic microorganisms. Proc Natl Acad Sci U S A 1998;95:3140–5. 12. Dingle KE, Colles FM, Wareing DR, Ure R, Fox AJ, Bolton FE, et al. Multilocus sequence typing system for Campylobacter jejuni. J Clin Microbiol 2001;39:14–23. 13. Enright MC, Day NP, Davies CE, Peacock SJ, Spratt BG. Multilocus sequence typing for characterization of methicillin-resistant and methicillin-susceptible clones of Staphylococcus aureus. J Clin Microbiol 2000;38:1008–15. 14. Feil EJ, Smith JM, Enright MC, Spratt BG. Estimating recombina- tional parameters in Streptococcus pneumoniae from multilocus sequence typing data. Genetics 2000;154:1439–50. 15. Nallapareddy SR, Duh RW, Singh KV, Murray BE. Molecular typing of selected Enterococcus faecalis isolates: pilot study using multilo- cus sequence typing and pulsed-field gel electrophoresis. J Clin Microbiol 2002;40:868–76. 16. Kotetishvili M, Stine OC, Kreger A, Morris JG Jr., Sulakvelidze A. Multilocus sequence typing for characterization of clinical and envi- ronmental Salmonella strains. J Clin Microbiol 2002;40:1626–35. 17. Noller AC, McEllistrem MC, Stine OC, Morris JG, Boxrud DJ, Dixon B, et al. Lack of DNA sequence diversity among Escherichia coli O157:H7 isolates that are distinct by pulsed-field gel electrophoresis. J Clin Microbiol 2003;41:675–9. 18. Farfan M, Minana-Galbis D, Fuste MC, Loren JG. Allelic diversity and population structure in Vibrio cholerae O139 Bengal based on nucleotide sequence diversity. J Bacteriol 2002;184:1304–13. 19. Mukhopadhyay AK, Chakraborty S, Takeda Y, Nair GB, Berg DE. Characterization of VPI pathogenicity island and CTXΦ prophage in environmental strains of Vibrio cholerae. J Bacteriol 2001;183:4737–46. 20. Ewing B, Greene P. Base-calling of automated sequencer traces using Phred. II. Error probabilities. Genome Res 1998;8:186–94. 21. Ewing B, Hillier L, Wendl M, Greene P. Base-calling of automated sequencer traces using Phred. I. Accuracy assessment. Genome Res 1998;8:175–85. 22. Green P. 1998. Phrap, SWAT and CrossMatch. Available from: URL: http://www.washington.edu 23. Jeanmougin F, Thompson JD, Gouy M, Higgins DG, Gibson TJ. Multiple sequence alignment with Clustal X. Trends Biochem Sci 1998;23:403–5. 24. Swofford D. PAUP* beta version. Sunderland (MA): Sinauer Assoc; 2000. 25. Beltran P, Delgrado G, Navarro A, Trujillo F, Selander RK, Cravioto A. Genetic diversity and population structure of Vibrio cholerae. J Clin Microbiol 1999;37:581–90. 26. Spratt BG, Maiden MCJ. Bacterial population genetics, evolution and epidemiology. Philos Trans R Soc Lond Biol Sci 1999;354:701–10. 27. Wallace B. Basic populations genetics. New York: Columbia University Press; 1981. p. 429–32. 28. Israel DA, Salama N, Krishna U, Rieger UM, Atherton JC, Falkow S, et al. Helicobacter pylori genetic diversity within the gastric niche of a single host. Proc Natl Acad Sci U S A 2001;98:14625–30. 29. Ford HD, Ford EB. Fluctuation in numbers, and its influence on vari- ation, in Melitaea aurina, Rott. (Lepidoptera). Transactions of the Royal Entomological Society London 1930;78:345–51. 30. Carson HL. The population flush and its genetic consequences. In: Lewontin RC, editor. Population biology and evolution. Syracuse (NY): Syracuse University Press;1968. p. 123–37. Address for correspondence: O. Colin Stine, Department of Epidemiology and Preventive Medicine, University of Maryland School of Medicine, Baltimore, MD 21201, USA; fax: 410-706-1644; email: ostin001@umaryland.edu 814 Emerging Infectious Diseases • Vol. 9, No. 7, July 2003