In vitro antimicrobial susceptibilities of Nocardia species

The in vitro activities of various quinolones, two new aminoglycosides, a new cephamycin analog (cefmetazole) and a new spectinomycin analog (trospectomycin), imipenem, and trimethoprim-sulfamethoxazole against 26 isolates of Nocardia asteroides, 7 isolates of N. brasiliensis, and 6 isolates of N. caviae were determined by a broth microdilution method. The three new quinolones, PD 117558, PD 117596 and PD 112739, inhibited 90% of N. asteroides at 1 to 2 micrograms/ml, and two new aminoglycosides, SCH 21420 and SCH 22591, inhibited 90% of N. asteroides at 2 to 4 micrograms/ml. Among the beta-lactams, cefmetazole was more active than imipenem. N. brasiliensis and N. caviae isolates were also very susceptible to the three quinolones (MICs for 50% of the isolates, 0.25 to 1 microgram/ml) and the two aminoglycosides (MICs for 50% of the isolates, 1 to 2 micrograms/ml). Cefmetazole was moderately active against N. brasiliensis, whereas imipenem showed poor activity against both of these species.