The antibiotic resistance pattern of 1921 Staphylococcus strains isolated from animals and food within the last two years were examined using diffusion tests. Among them there were only 35 strains of S. aureus having an inhibition zone diameter of 15 mm or less, and 4 strains of coagulase-negative staphylococci (CNS) having a zone diameter of 18 mm or less to 1-µg oxacillin disk. These 39 strains were examined also by E-test to oxacillin and for the detection of the mecA gene by PCR in order to determine whether they might be real methicillinresistant staphylococci. Among the 39 strains there were only two that were susceptible to penicillin by disk diffusion method; however, further examination by the penicillinase test showed that they produced β-lactamase. While 19 (15 S. aureus, 4 CNS) strains were resistant and 7 strains were intermediate to oxacillin in disk diffusion test, the E-test gave 8 resistant and 5 intermediate results. Six out of the 8 oxacillin-resistant strains examined by disk diffusion and E-test harboured the mecA gene. Thus only 6 out of the examined 1921 strains proved to be mecA positive. These methicillin-resistant, mecA-positive strains (5 of the S. aureus strains and 1 of the S. epidermidis) originated from two dairy herds. The results prove that methicillin-resistant S. aureus (MRSA) strains in animals are really rare in Hungary. Eighteen strains were chosen and screened for minimal inhibitory concentration (MIC) of oxacillin with or without clavulanic acid or sulbactam, and three of them produced methicillinase enzyme.
Background: Borderline methicillin resistance in Staphylococcus aureus is due to β-lactamase overproduction and/or specific methicillinases. Methods: β-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 β-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 β-lactamases were detected in the methicillin-resistant Staphylococcus aureus strain studied, but the susceptible strains possessed only the first enzyme. Conclusions: The 30-kDa β-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 β-lactamases published to date.
A new type ofβ-lactamase has been isolated and characterized in Streptomyces griseus NRRL B-2682. The enzyme has membrane-bound and extracellular forms. Biochemical characterization of some of the properties of the enzyme showed that it belongs to the class A group of penicillinases. Comparison of the membrane-bound and extracellular forms of theβ-lactamases suggests that they seem to be differently processed forms of the same enzyme. The N-terminal amino acid sequence of the extracellular form of the β-lactamase showed a high degree of similarity to a D-aminopeptidase of another Streptomyces griseus strain. Secretion of the β-lactamase was affected by the differentiation state of the strain since in spontaneous non-sporulating mutants only the membrane-bound form was present. In accordance with this when sporulation of the wild-type strain was inhibited it failed to secrete extracellular β-lactamase. Addition of globomycin to the non-sporulating cells liberated the enzyme from the membrane, indicating that the protein is processed normally by signal peptidase II and a glyceride-thioether group, together with a fatty acid amide-linkage, is responsible for the attachment of the enzyme to the cellular membrane. Under sporulation-repressed conditions addition of peptidoglycan fragments and analogues or inhibition of cell wall biosynthesis by penicillin-G induced β-lactamase secretion and also restored sporulation both in solid and submerged cultures. These results confirm that β-lactamase secretion is tightly coupled to the sporulation process in S. griseus.
Background: Mechanisms of borderline resistance of Staphylococcus aureus to penicillinase-resistant penicillins (PRPs) may include hyperproduction of classical penicillinase and/or production of β-lactamase hydrolyzing also PRPs. Methods: β-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 µg/ml, which were reduced by sulbactam and/or clavulanic acid in the case of four isolates producing large quantities of inducible, type A β-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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.