Role of a large plasmid in mediation of multiple drug resistance in Salmonella typhi and paratyphi A in Bangladesh.

From 405 patients of suspected typhoid fever, 94 Salmonella typhi and 17 Salmonella paratyphi A, were isolated from blood and/or stool at the Institute of Postgraduate Medicine and Research, Dhaka during March 1992 to February 1993. Forty seven percent of the isolates were resistant to multiple drugs which included amoxicillin, ampicillin, chloramphenicol and co-trimoxazole. A large plasmid of 140 MDa was isolated from 73% of multidrug resistant (MDR) strains. However, no plasmid was isolated from any of the strains sensitive to above mentioned antibiotics. Majority of MDR Salmonella transferred resistance to E. coli K-12 (Lac+, F-, NxR.) by conjugation method. The transconjugants were similarly resistant to multiple drugs. All Salmonella were sensitive to ciprofloxacin and ceftriaxone.