Z Gál1, P Kovács, F Hernádi, G Barabás, L Kiss, A Iglói, I Szabó. 1. Department of Pharmacology, Medical and Health Science Center, and Institute of Biochemistry, Faculty of Sciences, University of Debrecen, Debrecen, Hungary.
Abstract
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.
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.
Authors: Xiaoliang Ba; Ewan M Harrison; Giles F Edwards; Matthew T G Holden; Anders Rhod Larsen; Andreas Petersen; Robert L Skov; Sharon J Peacock; Julian Parkhill; Gavin K Paterson; Mark A Holmes Journal: J Antimicrob Chemother Date: 2013-11-11 Impact factor: 5.790