Transition of drug susceptibilities of Vibrio cholerae O1 in Lao People's Democratic Republic.

The changes of drug susceptibilities of Vibrio cholerae O1 isolated during the past 7 years (1993-1999) in Lao PDR were investigated. The most noteworthy finding was the appearance of polymyxin B sensitive El Tor vibrios. Until 1996, the susceptibilities were almost as expected and cholera disappeared in 1997. When a cholera outbreak resurfaced in 1998, the susceptibilities of isolated V. cholerae O1 against tetracycline, sulfamethoxazol-trimethoprim, chloramphenicol and polymyxin B were quite different from those of previously isolated organisms. Minimum inhibitory concentrations (MICs) of tetracycline and chloramphenicol against the isolates in 1998 were about 16 times higher than those against the previous isolates, and the MICs of sulfamethoxazol-trimethoprim were about 256 times higher than those against the previous isolates, (trimethoprim 32 microg/ml: sulfamethoxazol 608 microg/ml). Eleven percent of the isolates (11/99) were as sensitive to polymyxin B as the classic cholera vibrios (MIC < 2 microg/ml). In 1999, the susceptibility pattern was almost the same as that in 1998 except for polymyxin B to which 58% of the isolates (21/36) became sensitive.