[Mechanism of multiresistant Salmonella typhi].

From November 1988 to June 1989, 142 strains of S. typhi were isolated from patients of typhoid fever in Qingpu County, Shanghai These strains were highly sensitive to ceftazidime, ceftriaxone, ofloxacin and enoxacin, the sensitive rates to chloramphenicol, co-trimoxazole and ampicillin being from 67% to 83%. Of these 142 strains, twenty-two were multiresistant strains, being resistant to chloramphenicol, co-trimoxazole, ampicillin, cefazolin, gentamicin, piperacillin and tetracycline. Beta-lactamase production was the possible mechanism of resistance of S.typhi to beta-lactam antibiotics. Plasmid analysis by agarose gel electrophoresis showed that a plasmid band of 98Md was found in all multiresistant strains as well as the conjugates, while in sensitive strains, no plasmid band was found. The 98Md large plasmid seemed to be closely related to the multiresistance of S.typhi. Phage typing of S.typhi strains in Qingpu area revealed that M1 was the most prevalent type and A, E1, D2 etc followed in order of frequency. M1 type seemed to be closely related to the resistance to chloramphenicol, co-trimoxazole and ampicillin.