ABSTRACT
Oxacillin resistance was examined in 258 coagulase-negative staphylococci from Greek hospitals. mecA DNA was detected in 168 isolates, which were also resistant to oxacillin by agar dilution and disk diffusion, according to the current NCCLS breakpoints. Both methods exhibited a relatively low specificity misclassifying 21 and 19 of the 90 mecA-negative isolates respectively as oxacillin resistant. In contrast, an anti-PBP 2a latex agglutination test, applied after induction by oxacillin, correctly classified 163 mecA-positive (sensitivity 97%) and 88 mecA-negative isolates (specificity 97.7%).
Subject(s)
Bacterial Proteins , Carrier Proteins/analysis , Drug Resistance, Bacterial , Hexosyltransferases , Muramoylpentapeptide Carboxypeptidase/analysis , Oxacillin/pharmacology , Penicillins/pharmacology , Peptidyl Transferases , Staphylococcal Infections/microbiology , Staphylococcus/isolation & purification , Coagulase/metabolism , DNA, Bacterial/chemistry , DNA, Bacterial/genetics , Greece , Humans , Latex Fixation Tests/methods , Microbial Sensitivity Tests , Oxacillin/metabolism , Penicillin-Binding Proteins , Penicillins/metabolism , Polymerase Chain Reaction , Retrospective Studies , Staphylococcus/classification , Staphylococcus/genetics , Staphylococcus/metabolismABSTRACT
A sample of 450 consecutive, non-replicated coagulase-negative staphylococci (CoNS), collected from clinical specimens during the period 2000-2001 from the five major hospitals of Thessaly district (Central Greece) were investigated for resistance to methicillin. Most of the isolates had been collected in a sporadic fashion from the intensive care units and the surgical wards of the participating hospitals. The majority of the isolates (76%) were Staphylococcus epidermidis (50%), Staphylococcus haemolyticus (14.8%) and Staphylococcus hominis (11.1%). All 316 isolates (70%) were classified as resistant according to NCCLS breakpoints (MIC > or =0.5 mg/l); 268 (59.5%) of them were mecA-positive in a PCR-based assay. All isolates with MIC > or =8 mg/l carried the gene, while, only 23.8% of isolates with MIC, 0.5-4 mg/l were carriers. Only 9% of the mecA-positive isolates were found to be sensitive to various non-beta-lactams, while 41.8% of the isolates were resistant to more than three antimicrobial groups apart from beta-lactams. Molecular typing by PFGE showed apparent heterogeneity among isolates of each species and the absence of predominant clones.
Subject(s)
Cross Infection/microbiology , Methicillin/pharmacology , Penicillins/pharmacology , Staphylococcal Infections/microbiology , Staphylococcus/drug effects , Coagulase/analysis , Coagulase/genetics , Cross Infection/epidemiology , Genotype , Greece/epidemiology , Hospitals , Humans , Intensive Care Units , Methicillin Resistance/genetics , Microbial Sensitivity Tests , Staphylococcal Infections/epidemiology , Staphylococcus/enzymology , Staphylococcus/geneticsABSTRACT
A total of 250 consecutive Staphylococcus aureus clinical isolates were collected during the period 1999-2000 from the five major hospitals of the district of Thessaly (Central Greece). Thirty seven (14.8%) of the isolates were mecA-positive (MRSA) in a PCR-based assay; all exhibited resistance to oxacillin (agar dilution MICs > or =4 mg/L) and were also resistant to multiple antibiotics. Most of the MRSA isolates had been collected in the intensive care units and the surgical wards of the participating hospitals in a sporadic fashion. The MRSA incidence found here was significantly lower than reported in previous studies from Greece. Molecular typing by PFGE showed that the MRSA isolates were distributed between three pulsotypes. Evaluation of various conventional methods for assessing methicillin resistance showed that oxacillin agar dilution and immunological detection of PBP2a with the Slidex MRSA Detection kit were the most reliable in this setting. Misclassifications of isolates exhibiting low-level resistance (oxacillin MIC 2-4 mg/L) occurred with the salt agar screen, the oxacillin disk diffusion and the ATB Staph System methods.
