Induced in vitro Resistance of Staphylococci to Streptomycin and Penicillin

1. Under certain conditions strains of S. aureus develop resistance in vitro to streptomycin or to penicillin (G). 2. Greater variation occurs in the degree and rate at which resistance is acquired to penicillin than to streptomycin. 3. All of the streptomycin and penicillin-resistant strains studied showed some decrease in resistance upon transfer in broth free of the antibiotics. 4. Two of the penicillin-fast strains increased in resistance to streptomycin whereas the streptomycin-fast strains remained sensitive to penicillin. 5. Some streptomycin-fast staphylococcal strains show a change in pigment production and a reduction in the rate of carbohydrate fermentation.