In-vitro susceptibility testing of Nocardia spp. and its taxonomic implication.

By disc diffusion, 28 clinical isolates of four species of Nocardia were tested against 16 antimicrobial agents. Among the drugs included in the study, only a few exhibited in-vitro activities. A species difference in susceptibility was noted for amoxicillin + clavulanic acid, kanamycin, gentamicin, chloramphenicol, minocycline and erythromycin, which was of clinical and taxonomic interest. All six N. brasiliensis and six N. otitidis-caviarum were susceptible to gentamicin and minocycline, while all 15 N. asteroides were not. In addition, N. otitidis-caviarum was susceptible to kanamycin and chloramphenicol, while the sensitivity of N. farcinica was less predictable. The only antibiotic to which members of all of the Nocardia species tested were susceptible was amikacin, which therefore appears to be a good candidate for the treatment of all forms of nocardial infections.