Antibacterial activity of selected beta-lactam and aminoglycoside antibiotics against cephalothin-resistant Enterobacteriaceae.

The in vitro antibacterial activity of four beta-lactam antibiotics (cefatrizine [BL-S640], cefamandole, cefoxitin, and carbenicillin) and three aminoglycosides (amikacin, gentamicin, and tobramycin) was determined against 197 strains of cephalothin-resistant Enterobacteriaceae. Eighty strains were found to be gentamicin-sensitive, and 117 were found to be gentamicin-resistant. Carbenicillin was the most active beta-lactam antibiotic against gentamicin-sensitive Serratia marcescens and Enterobacter spp. Cefoxitin was the most active beta-lactam antibiotic against the remaining gentamicin-sensitive and -resistant Enterobacteriaceae, including Providencia stuartii and indole-positive Proteus spp. Cefatrizine exhibited little activity against the organisms studied. Cefamandole was less active than cefoxitin and carbenicillin. Amikacin was the most effective agent in vitro. With the exception of S. marcescens, cefoxitin appeared to be the next most promising agent in vitro against gentamicin- and cephalothin-resistant Enterobacteriaceae.