Z. Gal et al., Investigation of oxacillin-hydrolyzing beta-lactamase in borderline methicillin-resistant clinical isolates of Staphylococcus aureus, CHEMOTHERA, 47(4), 2001, pp. 233-238
Background: Mechanisms of borderline resistance of Staphylococcus aureus to
penicillinase-resistant penicillins (PRPs) may include hyperproduction of
classical penicillinase and/or production of beta -lactamase hydrolyzing al
so PRPs, Methods: beta -Lactamase activity of whole cells and purified enzy
mes was estimated spectrophotometrically and in isolated cytoplasmic membra
nes by bioassay with Bacillus subtilis as test strain. Results: Out of 53 c
linical isolates of S. aureus, 18 showed oxacillin MIC values from 0.5 to 2
mug/ml, which were reduced by sulbactam and/or clavulanic acid in the case
of four isolates producing large quantities of inducible, type A beta -lac
tamase. Cytoplasmic membranes isolated from these strains showed oxacillin-
hydrolyzing activity. One of these strains was grown also in the presence o
f globomycin, an antibiotic known to interfere with the anchorage of membra
ne lipoproteins; this treatment eliminated the oxacillin-hydrolyzing activi
ty. Conclusions: The resistance in these strains was due to a membrane-boun
d lipoprotein with oxacillin-hydrolyzing activity. Copyright (C) 2001 S.Kar
ger AG,Basel.