MOLECULAR EPIDEMIOLOGIC ANALYSIS OF VIBRIO-CHOLERAE O1 ISOLATES BY PULSED-FIELD GEL-ELECTROPHORESIS

Isolates of Vibrio cholerae O1 El Tor from two well-defined cholera ou tbreaks in Malaysia were analyzed by using pulsed-field gel electropho resis (PFGE). Isolates from sporadic cases occurring during the same t ime period mere also studied. Digestion of chromosomal DNA from these isolates of V. cholerae O1 with restriction endonucleases NotI (5'-GCG GCCGC3') and SfiI (5'-GGCCNNNN-3'), followed by PFGE, produced restric tion endonuclease analysis (REA) patterns consisting of 13 to 24 bands (ranging in size from 46 to 398 kbp). Analysis of the REA patterns ge nerated by PFGE after digestion with NotI and SfiI suggested the clona l nature and close genetic identity of the isolates obtained during ea ch of the two outbreaks (Dice coefficient, 0.93 to 1.0). Although they had very similar REA patterns, the two outbreak clones were not ident ical. Isolates of V. cholerae O1 from sporadic cases, on the other han d, appeared to be much more heterogeneous (five different REA patterns detected in the five isolates tested; Dice coefficient, 0.31 to 0.81) than those obtained during the two outbreaks. We conclude that PFGE o f V. cholerae O1 chromosomal DNA digested with infrequently cutting re striction endonucleases is a useful method for molecular typing of V. cholerae isolates for epidemiological purposes.