Evidence for a methicillin-hydrolysing β-lactamase in Staphylococcus aureus strains with borderline susceptibility to this drug |
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Authors: | Orietta Massidda Maria Pia Montanari Pietro Emanuele Varaldo |
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Affiliation: | Dipartimento di Biologia Molecolare, Sezione Microbiologia, Università degli Studi di Siena, Italy. |
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Abstract: | A new beta-lactamase that hydrolyses methicillin was found in the membrane fraction of two clinical isolates of Staphylococcus aureus with borderline susceptibility to this drug. 'Methicillinase' activity was detected in renatured sodium dodecyl sulfate polyacrylamide gel electrophoretograms of staphylococcal membrane proteins. The enzyme activity appeared to be inducible and was more easily detected using penicillin G (or methicillin) rather than nitrocefin as substrate. Similar activity was not detected in the membrane fraction of a methicillin-susceptible strain. These results suggest that, in the two borderline susceptible strains, rather than a hyperproduction of the penicillinase a specific methicillin-hydrolysing activity is responsible for the borderline susceptible phenotype. |
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Keywords: | Staphylococcus aureus Penicillinase-resistant penicillin (PRP) Borderline susceptibility β-Lactamase |
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