Rapid testing methods for the detection of methicillin-resistance Staphylococcus aureus

Abstract

Appropriate early antimicrobial therapy of patients with serious infections caused by S. aureus is well recognized as an important factor for a favorable outcome. The fact that MRSA strains often are multi-resistant leaves only few antibiotics available for the therapy of MRSA infections. As a consequence, clinicians in many countries resort to the use of glycopeptides to broadly cover the patient for a possible MRSA infection until the results of cultures and susceptibility testing are available. Such use of glycopeptides clearly increases the selective pressure for vancomycin resistance, an issue which is of great concern in view of the increasing problem with vancomycin-resistant enterococci. Moreover, there is an additional risk that the overuse of vancomycin may lead to the development of vancomycin-resistant stains of MRSA, a situation for which no treatment would be available! Finally, therapy with glycopeptides results in higher cost as compared to ß-lactamase stable penicillins due to the higher cost of the drug as well as higher associated costs of therapy such as vancomycin levels. Rapid/accurate detection of MRS A is important in order to decrease the use of glycopeptide antibiotics. Furthermore, rapid and accurate detection increases the possibilities of reducing or even controlling the spread of MRSA. DNAbased rapid assays have been developed and should be available commercially soon. At present, these rapid assays are also being evaluated against methicillin resistance in coagulase negative staphylococci (CNST). Such resistance is also encoded by the mecA gene. CNST infections are increasing, especially in immunocompromised patients with methicillin resistance being very common in these strains. The existing phenotypic susceptibility methods detection of methicillin resistance is so unreliable when testing CNST that many clinicians choose to treat with glycopeptide antibiotics regardless of the test results.