beta-lactamase production in coagulase-negative micrococcaceae.

A total of 8 penicillin-susceptible and 55 penicillin-resistant coagulase-negative Micrococcaceae were investigated for their beta-lactamase production by one quantitative and three qualitative methods. Seven of the 8 penicillin-susceptible strains had no beta-lactamase production; one had a very low production. Among the 55 penicillin-resistant strains, 54 produced beta-lactamase (mean 63 units/mg bacteria). Methicillin/gentamicin-resistant strains produced less enzyme than strains susceptible to these antibiotics. The percentage extracellularity (mean 18%) was lower than in Staphylococcus aureus, whereas the induction ratio (mean 56) was higher. No significant difference between the different species could be observed, but 70% of the strains were Staphylococcus epidermidis. Among the 55 beta-lactamase producing strains, the microbiological clover-leaf method detected 51, the iodometric method 40 and the chromogenic cephalosporin method 38. None of the three qualitative methods gave any false positive reactions.