Resistance of Shigellae to Ampicillin and Other Antibiotics

Ampicillin resistance among shigellae has increased in the Washington area from 6% to 95% during the past four years. This parallels a similarly high incidence recently reported from England. There has been a concomitant but lesser increase in resistance to carbenicillin, the cephalosporins, tetracycline, and streptomycin. Chloramphenicol has remained effective in vitro. Aminoglycosides such as kanamycin, gentamicin, and neomycin have also maintained their in vitro efficacy against shigellae. There has also been a rapid increase in the development of multiresistant strains of shigellae. In this study, resistance patterns to sulfonamides, streptomycin, tetracycline, and ampicillin were common. Multiple drug resistance of shigellae was shown to be mediated by R-factor. The rapid spread of multiple resistance induced by R-factor among shigellae may be related to intensive use of ampicillin and other antibiotics during the past few years.