THE POSTANTIBIOTIC EFFECT OF SELECTED ANTIBIOTICS ON STAPHYLOCOCCUS-AUREUS NEWBOULD-305 FROM BOVINE INTRAMAMMARY INFECTION

The postantibiotic effect (PAE) was determined for selected antibiotics against Staphylococcus aureus Newbould 305 originating in vivo from mastitic milk and compared with the PAE for the same S. dureus strain cultured in vitro. The PAE was measured at 2 and 4 rimes the MIC for I and 2 h of exposure. The PAE of penicillin, pirlimycin, and tirmicosin were reduced against S. aureus 305 originating in vivo compared with S. aureus 305 grown in vitro. The PAE of cephapirin was increased against S. aureus originating in vivo. Minimal effect on PAE was noted for novobiocin. The PAE for rifampicin extended beyond the limits of the test parameters (> 180 min) for an antibiotic concentrations, media, and exposure times tested, except at 2 times the MIC and at 1 h exposure when the PAE was reduced to 60 min for S. dttreus 305 originating in vivo. The PAE of an antibiotic may be an important consideration in determining therapy intervals and antibiotic concentrations for treatment of bovine mastitis.