Antibiotic sensitivity of some nocardioform bacteria and its value as a criterion for taxonomy.

We tested 151 strains representing the genera Nocarclia and Gordma, the taxon ‘ Mycobacterium ’ rhodochrous and a collection of strains isolated from bagasse for their in vitro susceptibility to 52 antimicrobial agents by using the impregnated filter-paper disc method. The ‘ bagasse’ isolates were resistant to most of the antimicrobial agents but the nocardiae, gordonae and rhodochrous groups formed a series with increasing sensitivity. The nocardiae were inhibited by low concentrations of a number of antibiotics, notably erythromycin, micoiiazole, gentamycin and tobramycin, which may be of value in treating Nocardia infections. Certain antibiotics, at suitable concentrations, provided data of value for the classification and identification of nocardioform bacteria.