Investigation of oxacillin-hydrolyzing beta-lactamase in borderline methicillin-resistant clinical isolates of Staphylococcus aureus.
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 also PRPs.


METHODS
beta-Lactamase activity of whole cells and purified enzymes was estimated spectrophotometrically and in isolated cytoplasmic membranes by bioassay with Bacillus subtilis as test strain.


RESULTS
Out of 53 clinical isolates of S. aureus, 18 showed oxacillin MIC values from 0.5 to 2 microg/ml, which were reduced by sulbactam and/or clavulanic acid in the case of four isolates producing large quantities of inducible, type A beta-lactamase. Cytoplasmic membranes isolated from these strains showed oxacillin-hydrolyzing activity. One of these strains was grown also in the presence of globomycin, an antibiotic known to interfere with the anchorage of membrane lipoproteins; this treatment eliminated the oxacillin-hydrolyzing activity.


CONCLUSIONS
The resistance in these strains was due to a membrane-bound lipoprotein with oxacillin-hydrolyzing activity.
Gál
Z
Z
Department of Pharmacology, Medical and Health Science Center, and Institute of Biochemistry, Faculty of Sciences, University of Debrecen, Debrecen, Hungary.
Kovács
P
P
Hernádi
F
F
Barabás
G
G
Kiss
L
L
Iglói
A
A
Szabó
I
I
D006801:Humans; D006868:Hydrolysis; D016106:Methicillin Resistance / Q000235:genetics / Q000502:physiology*; D010068:Oxacillin / Q000378:metabolism* / Q000494:pharmacology; D010406:Penicillins / Q000378:metabolism* / Q000494:pharmacology; D013211:Staphylococcus aureus / Q000145:classification / Q000187:drug effects* / Q000201:enzymology; D001618:beta-Lactamases / Q000502:physiology*
D010406:Penicillins; D001618:beta-Lactamases; D010068:Oxacillin