Antimicrobial susceptibilities of regional pathogenic strains of Nocardia isolated from mycetomas

The activity of antimicrobial agents against clinical isolates of Nocardia was studied by determination of the Minimal Inhibitory Concentrations (MICs) and Disk Diffusion Technique, according to the National Committee for the clinical Laboratory Standards (NCCLS). The object was: (a) to determine the 'in vitro' susceptibility of the strains that cause human mycetomas; (b) to determine the presence of different patterns of sensitivity among the regional strains; (c) to evaluate the Disk Diffusion Technique using disks commercially available with the antimicrobial concentrations normally used in the microbiological practice. Comparing the MIC values obtained with the values suggested by the National Committee for Clinical Laboratory Standards for Nocardia spp. (broth microdilution MIC breakpoints), we found that local strains are susceptible to amikacin, cefotaxime, ceftriaxone and TMP-SMZ; moderately susceptible to ampicillin and resistant to ciprofloxacin and erythromycin. The results obtained by both methods showed the presence of different patterns of sensitivity among the regional strains of N. brasiliensis. This showed strains sensitive and resistant to antibiotics. The Disk Diffusion Technique, even if it is not the adequate method to study the sensitivity patterns of different strains against antimicrobial agents, permits the differentiation between strains sensitive and resistant to antibiotics.