Evaluation of screening and commercial methods for detection of methicillin resistance in coagulase-negative staphylococci.

The National Committee for Clinical Laboratory Standards recommends 48 h of incubation by the oxacillin salt agar screen (OSAS) method for the detection of methicillin-resistant coagulase-negative staphylococci (CoNS). An earlier identification of methicillin resistance is desirable. The time to detection of the mecA gene by PCR was compared with the times to detection by OSAS, by the oxacillin disk diffusion (ODD) method, and with MicroScan Gram Positive Combo type 6 panels (MicroScan Inc. Sacramento, Calif.) and Vitek GPS-SA cards (bioMérieux Vitek Inc., Hazelwood, Mo.). The combination of the Vitek card and the ODD method detected 92 of 99 methicillin-resistant strains of CoNS at 24 h; however, 6 mecA-positive strains were phenotypically methicillin susceptible. We conclude that most methicillin-resistant CoNS can be detected and the results can be reported after overnight incubation by a combination of methods.

Polymerase chain reaction-and RNA hybridization-based method for the investigation of deep-seated candidiasis.

OBJECTIVE: To determine the usefulness of a polymerase chain reaction (PCR) and RNA hybridization method for the diagnosis of invasive candidiasis and to compare its sensitivity with blood cultures. DESIGN: Blood cultures and a blood sample for PCR were taken from patients with suspected invasive candidiasis. A 105 base pair conserved segment within the rDNA of Candida species was amplified. The amplicon was detected by hybridization and gel electrophoresis. SETTING: Intensive care units of two tertiary care hospitals. PATIENTS: One hundred and eighteen patients 16 years of age or older with four more risk factors for invasive candidiasis were enrolled. Present or recent past treatment with broad spectrum antibiotics, cancer chemotherapy, immunosuppressive drugs, granulocytopenia or granulocytosis, intravascular catheterization, tracheal intubation, recent abdominal surgery and parenteral nutrition were considered risk factors. RESULTS: Forty-three patients had invasive candidiasis. PCR detected infections in 28 and 26 patients (sensitivity 65.1% and 60.4%) by hybridization and gel electrophoresis, respectively. The sensitivity of blood cultures was 58.1%. Of 25 patients with positive blood cultures, 17 were positive by PCR with the hybridization method. Eleven patients with invasive candidiasis had negative blood cultures but were positive by PCR. CONCLUSION: PCR, especially with a hybridization detection method, is more sensitive than blood culture for invasive candidiasis and may facilitate the diagnosis of nonfungemic disease.