Resistance to trimethoprim and other antibiotics in shigellae isolated in the province of Ontario.

Antimicrobial susceptibility determinations for three commonly used and seven seldom used antibacterial drugs against 482 strains of shigellae isolated in Ontario during 1977 and 1978 were carried out. Resistance to the first-line treatment drugs, ampicillin and tetracycline, occurred in 20.5 and 39.2% of strains, respectively. The emergence of trimethoprim-sulfamethoxazole resistance was noted for the first time in 3.2% of the strains in 1978. All strains retained their susceptibility to gentamicin, nalidixic acid, and polymyxin but were variably susceptible to chloramphenicol, cephalexin, and rifampin.