Evaluation of MRSASelect for Detecting Methicillin-Resistant Staphylococcus aureus from Surveillance Specimens / 병원감염관리

ABSTRACT

BACKGROUND: A rapid and sensitive surveillance culture has a pivotal role in infection control of methicillinresistant Staphylococcus aureus (MRSA). This study was aimed to compare the performance of MRSASelect (Bio-Rad, France) to that of mannitol salt agar containing 6 microgram/mL of oxacillin (MSA-OX) for detecting MRSA in surveillance cultures. METHOD: From May to June 2006, 86 nasal swabs and 21 sputum specimens were enrolled. All specimens were inoculated onto MRSASelect and MSA-OX, which were incubated for 2 days and 3 days, respectively, and colonies were read daily by a technologist. Pink colonies on MRSASelect and yellow colonies on MSA-OX were examined with Gram stain, Pastorex(R) Staph-plus (Bio-Rad) and mecA-PCR. After the final reading, both media were re-examined by a superviser. RESULTS: Of the 107 specimens cultured, 32 (29.9%) were positive for MRSA. Of these, 27 were detected by both media, one by MSA-OX only, and 4 by re-examination. The day-1 and day-2 sensitivities/specificities of MRSASelect were 78.1%/97.3% and 84.4%/97.3%, respectively, while those of MSA-OX were 53.1%/100% and 78.1%/92.1%, respectively. With MRSASelect, two more positives were detected at day 2, but their incubation was less than 18 hour at day 1. There were six false positive organisms detected three Enterobacter spp., one Acinectobacter spp., and two coagulase-negative staphylococci (CNS). But, the two CNS grew on MSA-OX only. CONCLUSION: MRSASelect with 1-day incubation showed a sensitivity equivalent to and a specificity better than MSA-OX with 2-day incubation. MRSASelect should be a useful medium for MRSA surveillance when it is read after an incubation of 18-28 hours with the confirmatory Gram stain of screen-positives.