Divergent disk susceptibility of coagulase-negative staphylococci to penicillinase-resistant penicillins and augmentin (amoxycillin/clavulanic acid).

30 representative intrinsically penicillin-resistant coagulase-negative staphylococcal (CONS) isolates yielded discrepant agar disk diffusion test (Bauer-Kirby) results for augmentin. Clavulanic acid (2.5 micrograms/ml) enhanced the activity of amoxycillin from 8- to greater than or equal to 128-fold (mean = 26-fold); MICs of amoxycillin (combined with 2.5 micrograms/ml clavulanate) ranged from 1-16 (mean = 3) micrograms/ml. It is recommended that clinical microbiology laboratories withhold 'susceptible' augmentin disk tests results from their reports regarding intrinsically penicillin-resistant CONS isolates. No such discrepancies were encountered among clinical isolates of Staphylococcus aureus.