In vitro susceptibility of Mycobacterium fortuitum to N-formimidoyl thienamycin and several cephamycins

The comparative in vitro activity of N-formimidoyl thienamycin, cefmetazole, cefoxitin, cefotetan (YM-09330), and moxalactam against 13 isolates of Mycobacterium fortuitum was evaluated by agar dilution susceptibility testing. N-Formimidoyl thienamycin inhibited 10 to 12 strains at 6.25 micrograms/ml, cefmetazole inhibited 12 of 13 strains at 12.5 micrograms/ml, cefoxitin inhibited 11 of 13 strains at 25 micrograms/ml, and cefotetan inhibited 11 of 13 strains at 50 micrograms/ml. Moxalactam was less active than the other compounds tested, inhibiting only 9 of 13 strains at 50 micrograms/ml.