a large pool of antibiotic resistant and auxotrophic mutants was isolated from the staphylococcus aureus phage group 2 strains ut0002-19 and ut0017 by ( 1 ) antibiotic gradient plates , ( 2 ) trimethoprim selection , and ( 3 ) nitrosoguanidine mutagenesis , which sometimes was coupled by enrichment with either penicillin or methicillin .
C0030842
penicillin
C0025643
methicillin