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.

beta-Lactam susceptibility patterns and investigation of cephalosporin hydrolysing beta-lactamases of Gram-negative extraintestinal clinical isolates.

Of more than 3500 isolates of enterobacteriaceae, 48-69% were resistant to aminopenicillins and 11-45% to amoxycillin+clavulanic acid. Resistance to second and third generation cephalosporins was present in 11-17 and 3-8% of Escherichia coli, 47-56 and 15-52% of Klebsiella-Enterobacter, 36-57 and 16-27% of Proteus, Providencia and Morganella isolates. Pseudomonas aeruginosa strains varied in their resistance to antipseudomonal beta-lactams.

A synthetic gamma-lactone group with beta-lactamase inhibitory and sporulation initiation effects.

Previous studies showed that some lactones have beta-lactamase inhibitory or antibacterial effects, others--like A-factor (a gamma-butyrolactone) and its derivatives--stimulate sporulation in Streptomyces griseus strains. Our experiments were aimed at exploring whether synthetic gamma-lactones had such effects. None of the seven gamma-lactones studied showed antibacterial activity, but two of them inhibited beta-lactamases isolated from various bacteria.