Methicillin resistance study in clinical isolates of coagulase-negative staphylococci and determination of their susceptibility to alternative antimicrobial agents

Aims: To achieve reliable detection of methicillin resistance in clinical i solates of coagulase-negative staphylococci. Methods and Results: Strains (105) were evaluated by normatized antimicrobi al susceptibility methods, and for the presence of the methicillin resistan ce-determining mecA gene, using the polymerase chain reaction. Correlation between phenotypic and genotypic methods was obtained in 87.6% of the sampl es. Six strains, classified as methicillin-susceptible by phenotypic assays , revealed the presence of the mecA gene, indicating that methicillin, resi stance expression was probably repressed. Another seven isolates failed to show mecA amplification after displaying methicillin resistance in phenotyp ic evaluations. The susceptibility of the methicillin-resistant isolates to other antimicrobial agents was variable. Conclusions: Genotypic determination of the mecA gene proved to be the most reliable method for detection of methicillin resistance. Significance and Impact of the Study: Correct assessment of methicillin res istance, such as that attained through genotyping, is essential for definin g therapeutic strategies, particularly when treating severely compromised p atients.