Use of a novel selective medium to detect methicillin-resistant Staphylococcus aureus in colonized patients of an intensive care unit.

Abstract

Detection of colonized patients is important for implementing control measures for methicillin-resistant Staphylococcus aureus (MRSA). Laboratory detection of MRSA carriers is increased by the use of selective screening media, helping control dissemination of such organisms. To evaluate three different media, including selective and nonselective media, in the detection of MRSA from clinical specimens of patients of an intensive care unit (ICU). Adult patients in the ICU of the Hospital Mãe de Deus, Porto Alegre, Brazil. A total of 224 specimens were obtained from the nares of patients and plated on blood agar, mannitol salt agar containing 2 microg/mL of oxacillin (MSAO), and oxacillin resistance screening agar base (ORSAB). The presence of MRSA was investigated in typical colonies growing on the three types of media. Discrepant results were resolved by detection of the mecA gene by polymerase chain reaction and the modified penicillin binding protein known as PBP2'. MRSA was detected in 32 (14.3%) of 224 specimens. Blood agar, MSAO, and ORSAB detected MRSA in 17, 31, and 28 specimens, respectively. After the coagulase test, no false resistance was observed. MSAO and ORSAB performed equivalently in the detection of MRSA of colonized patients and require a single supplementary test (coagulase) to confirm MRSA.