[Study on the rapid, secondary-growth mutants of Staphylococcus epidermidis (author's transl)].

Abstract

According to colony type, growth rate and development of secondary growth on the proteose-peptone No. 3 mannitol salt agar (PMS) and the nutrient agar (NA) media, Staphylococcus epidermidis may be classified into three groups. Group I includes strains which develop smooth colonies on both media. Group II consists of those which show rapid propagation of entire clones and develop secondary growth on the PMS medium, but grow only smooth colonies on the NA medium, and which may be called reversible mutants. Group III includes thoes which show secondary growth on both PMS and NA as well as other media, which may be called irreversible mutants. One percent proteose-peptone No. 3 and 5--7% NaCl are the essential ingredients for the induction of mutation, and mannitol can enhance it. Except the high sensitivity of the reversible mutants of human origin, the three groups of chicken origin showed similar drug susceptibility to biosynthesis inhibitors of protein and cell wall. On the HI medium, chloramphenicol inhibited secondary growth of irreversible mutants at 25.0 microgram/ml minimal antimutagenesis concentration (MAC), whereas streptomycin, penicillin, erythromycin and oxytetracycline did not at all. The irreversible mutants had higher resistance to biosynthesis inhibitors of DNA or RNA, e.g. mitomycin C (MMC), novobiocin (NOV) and rifampicin (RIF), than the other two groups. On the HI medium, MMC at the MAC of 0.16 microgram/ml, NA at 25.0 microgram/ml and NOV at 2.5 microgram/ml inhibited the secondary growth of irreversible mutants, but RIF did not. To the irreversible mutants, the MIC and MAC of NA on the PMS medium were both higher than those on the HI medium. The MACs of MMC and NOV on the PMS medium were also higher than those on the HI medium, but their geometric mean MIC remained almost unchanged on both media. Because the MACs of MMC (0.31 microgram/ml) and NA (100.0 microgram/ml) to the reversible mutants on the PMS medium were much similar to those of the irreversible mutants, it suggests that both groups had the similar mutation mechanism.