LABORATORY EVALUATION OF SEMISYNTHETIC ANTIBIOTICS AGAINST STAPHYLOCOCCI ISOLATED FROM BOVINE UDDER

Abstract

A comparison was made of the minimal inhibitory concentrations (MIC) of penicillin G, methicillin, oxacillin, and cephalosporin C for 16 non-penicillinase-producing strains of Staphylococcus aureus from cows with mastitis and on 22 penicillinase-producing strains (20 from cows with mastitis and 2 from humans), All strains were sensitive to methicillin, oxacillin, and cephalosporin C. The addition of whole or skim milk did not affect the tests. Strains with induced resistance to one of the three latter antibiotics developed resistance to the other two. By increasing the inocula of organisms in the test, the MIC was increased to the greatest extent with penicillin, to some extent with oxacillin, and negligibly with the other two antibiotics.