Variable antibiotic susceptibility patterns among Streptomyces species causing actinomycetoma in man and animals

Background: Drug therapy is recommended in conjunction with surgery in treatment of actinomycetoma. The specific prescription depends on the type of bacteria (actinomycetoma) or fungi (eumycetoma) causing the disease and their in vitro antimicrobial susceptibility. Objectives: To investigate the antimicrobial susceptibility among isolates of Streptomyces spp. isolated from cases of actinomycetoma in man and animals in Sudan. Methods: Streptomyces strains (n = 18) isolated from cases of actinomycetoma were tested in vitro against 15 commonly prescribed antibacterial agents using MIC agar dilution method as per standard guidelines. Results: Streptomyces strains isolated from actinomycetoma fall into various phenotypic groups. All of the strains were inhibited by novobiocin (8 mu g/mL), gentamycin (8, 32 mu g/mL) and doxycycline (32 mu g/mL). Fusidic acid (64 mu g/mL) inhibited 94.4% of the strains; bacitracin, streptomycin, cephaloridine, clindamycin, ampicillin, rifampicin and tetracycline (64 mu g/mL) inhibited between 61.1 and 77.8% of the strains. All strains were found resistant to amphotericin B (64 mu g/mL), penicillin (20 mu g/mL) and sulphamethoxazole (64 mu g/mL). Conclusions: Saprophytic Streptomyces spp. cause actinomycetoma in man and animal belong to separate phenotypes and have a wide range of susceptibility patterns to antimicrobial agents, which pose a lot of difficulties in selecting effective in vivo treatment for actinomycetoma.