Studies on the Penicillinase of Staphylococcus albus.

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Abstract
Summary and conclusions The properties of penicillin G-beta-lactamase from 12 strains of Staph. albus (Staph. epidermidis) were compared with those of Staph. aureus 60/1. The enzymes from both sources were similar in that: 1) they were inducible; 2) they were intra as well as extracellular; the extracellular enzymes were filterable through Millipore filters of 0.3 μ porosity, but not through Seitz filters; 3) their pH optima were close (pH 6.4–6.6). The enzyme activities of acetone-ether extracted cells of 24 hr-induced broth cultures of Staph. albus varied from 0.1–80.3 units/ml (pH 6.4, 37°C); that of corresponding Staph. aureus cells was 18.2 units/ml. Vmax values varied over a similar range. Km values varied from 9.1 to 83.3 μM penicillin G for Staph. albus strains; Km for Staph. aureus 60/1 was 10.0 μM. There was a close correlation between MIC and enzyme activity for Staph. albus strains, particularly when activity was measured at substrate conc. equal to MIC (Fig. 4). When thus compared, the strains fell into 2 distinct groups, one comprising 5 methicillin-resistant strains (MIC ≥ 12.5 μg/ml) and the other the methicillin-sensitive ones (MIC ≤ 6.25 μg/ml). It is concluded that the level of resistance to penicillin G in Staph. albus is the result of both the activity of the penicillinase it produces and the level of its “inherent”or natural resistance, the latter being higher for the methicillin-resistant than for the methicillin-sensitive cells.