ABSTRACT
In this study the susceptibility of 58 coagulase-negative staphylococci (CoNS) strains and 58 Staphylococcus aureus strains to oxacillin was evaluated by a novel method called quantitative disk diffusion (DD) method. The results obtained were compared to phenotypic methods as agar dilution (AD) for oxacillin, disk diffusion (DD) for cefoxitin, and related to the presence of the mecA gene detected by PCR. Minimum inhibitory concentrations (MIC) determined by the quantitative DD method were equivalent to MICs determined in the AD method for S. aureus (Student's t test, p=0.99) and CoNS (Student's t test, p=0.97). Incongruent results between PCR mecA gene determinations and the quantitative DD method were obtained in 8 strains (5 S. aureus and 3 CoNS) where the mecA gene expression was blocked. However, oxacillin resistance was detected by the proposed method even in staphylococci strains showing low-level or heterogeneous resistance to the antibiotic while other phenotypic methods failed. The single quantitative DD method is not expensive, it can be performed in any laboratory and permits accurate identification of oxacillin resistant staphylococci.
Subject(s)
Cefoxitin/pharmacology , Diffusion , Drug Resistance, Bacterial , Microbial Sensitivity Tests/methods , Oxacillin/pharmacology , Staphylococcus/drug effects , Agar , Bacterial Proteins/metabolism , Penicillin-Binding Proteins , Staphylococcus/pathogenicity , Staphylococcus/physiologyABSTRACT
No Brasil, enterococos resistente à vancomicina (VRE) têm sido descritos como patógenos hospitalares, desde 1998. Durante um monitoramento de VRE em um hospital, foram detectadas duas cepas de Enterococcus faecalis com genótipo vanA, e sensibilidade à teicoplanina. Este é o primeiro relato do isolamento de enterococo fenótipo VanB e genótipo vanA de amostra clínica no Brasil.
Subject(s)
Cross Infection , Enterococcus faecalis , In Vitro Techniques , Gram-Negative Bacterial Infections , Phenotype , Drug Resistance , Vancomycin , Genotype , MethodsABSTRACT
Fifty-one vancomycin-resistant enterococci samples isolated from different geographic regions in Brazil were studied. All the isolates harboured the vanA gene as demonstrated by PCR analysis, and in a majority of strains the gene was associated with a transferable plasmid of 70 kb. A single variant of the prototype Tn1546 associated with common transferable vanA-containing plasmids has spread among the enterococcal strains circulating in Brazil. The VanA element integrity in these enterococci strains and the different pulsed-field gel electrophoresis patterns suggest horizontal transmission of the vancomycin resistance transposon in Brazilian strains.
Subject(s)
Bacterial Proteins/genetics , Carbon-Oxygen Ligases/genetics , DNA Transposable Elements , Enterococcus faecalis/genetics , Enterococcus faecium/genetics , Plasmids , Electrophoresis, Gel, Pulsed-Field , Enterococcus faecalis/drug effects , Enterococcus faecium/drug effects , Polymerase Chain Reaction , Vancomycin ResistanceABSTRACT
The aim of this study was to evaluate the accuracy of cefoxitin disc diffusion as a prediction of oxacillin resistance in coagulase-negative staphylococci (CoNS), and also to compare genotypic and phenotypic methods for detecting this resistance property. A total of 151 clinical CoNS isolates were tested by PCR for the presence of the mecA gene (gold standard method). The isolate susceptibilities were determined by the disc diffusion method with oxacillin (1 microg) and cefoxitin (30 microg) and by the agar dilution method for cefoxitin and oxacillin. Although none of the techniques showed 100% sensitivity and 100% specificity, the cefoxitin disc diffusion and oxacillin agar dilution were the best methods for detecting resistance to oxacillin among CoNS as these methods produced the best negative and positive predictive values. A combination of methods can be used routinely to identify resistance to oxacillin in CoNS.