Investigation of beta-Lactamases in clinical isolates of Staphylococcus aureus for further explanation of borderline methicillin resistance.
BACKGROUND
Borderline methicillin resistance in Staphylococcus aureus is due to beta-lactamase overproduction and/or specific methicillinases.


METHODS
beta-Lactamase activity in culture supernatants and in cytoplasmic membrane fractions was estimated by bioassay and by SDS-PAGE combined with nitrocefin assay.


RESULTS
During the investigation of borderline methicillin-resistant Staphylococcus aureus (BORSA) strains VU94 and 822 two beta-lactamases were detected in the membranes, with molecular weights of 13 and 30 kDa. The latter could be found in the culture supernatants, too. In the presence of globomycin, this enzyme disappeared from the membrane, and the oxacillin-hydrolyzing activity of the membrane decreased to the level of susceptible strains. Both beta-lactamases were detected in the methicillin-resistant Staphylococcus aureus strain studied, but the susceptible strains possessed only the first enzyme.


CONCLUSIONS
The 30-kDa beta-lactamase proved to be a methicillinase, and it can be one of the main causes of the borderline phenotype of BORSA strains. The other enzyme is one of the smallest beta-lactamases published to date.
Keseru
Judit Szilvia
JS
Department of Human Genetics, University of Debrecen, Hungary. kevia@freemail.hu
Gál
Zsuzsanna
Z
Barabás
Gyorgy
G
Benko
Ilona
I
Szabó
István
I
D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism; D016106:Methicillin Resistance / Q000502:physiology*; D008826:Microbial Sensitivity Tests; D013211:Staphylococcus aureus / Q000145:classification / Q000187:drug effects* / Q000201:enzymology*; D001618:beta-Lactamases / Q000378:metabolism*
D008565:Membrane Proteins; D001618:beta-Lactamases