MOLECULAR TYPING OF SALMONELLA-TYPHI STRAINS FROM DHAKA (BANGLADESH) AND DEVELOPMENT OF DNA PROBES IDENTIFYING PLASMID-ENCODED MULTIDRUG-RESISTANT ISOLATES

Seventy-eight Salmonella typhi strains isolated in 1993 and 1995 from patients living in Dhaka, Bangladesh, were subjected to phage typing, ribotyping, IS200 fingerprinting, and PCR fingerprinting. The collecti on displayed a high degree of genetic homogeneity, because restricted numbers of phage types and DNA fingerprints were observed. A significa nt number of the S. typhi strains (67%) were demonstrated to be multip le drug resistant (MDR). The vast majority of the MDR strains were res istant to chloramphenicol, ampicillin, trimethoprim, streptomycin, sul famethoxazole, and tetracycline (R type CATmSSuT) a resistance phenoty pe that has also frequently been observed in India, Only two strains d isplayed a distinct MDR phenotype, R type AT-mSSuT. Pulsed-field gel e lectrophoresis demonstrated the presence of large plasmids exclusively in the MDR strains of both R types. The plasmids present in the S. ty phi strains of R type CATmSSuT could be conjugated to Escherichia coli and resulted in the complete transfer of the MDR phenotype. PCR finge rprinting allowed discrimination of MDR and susceptible strains. The D NA fragments enabling discrimination of MDR and susceptible S. typhi s trains by PCR were useful genetic markers for identifying MDR encoded by large plasmids of the H1 incompatibility group.