Evaluation of MRSASelect for Discrimination of Methicillin-resistant Staphylococcus aureus from Other Staphylococci

Kim, Yong Kyun; Kim, Jae Seok; Lee, Hyoung Sun; Song, Wonkeun; Kim, Han Sung; Park, Ji Young; Cho, Hyoun Chan; Lee, Kyu Man

Abstract

BACKGROUND
It is now recognized that screening for methicillin-resistant Staphylococcus aureus (MRSA) in hospital is an effective infection control measure, and selective media-based methods have been commonly used. MRSASelect (MRSAS; Bio-Rad, Hercules, CA, USA) is MRSA selective agar incorporating chromogenic enzymatic substrates, and have been found to be more sensitive and specific than other selective media. The aim of present study was to evaluate MRSAS for discrimination of MRSA from other staphylococci by comparison with mannitol-salt agar with oxacillin (MSO) which is widely used as a MRSA selective medium.
METHODS
Ninety-eight staphylococcal strains which were isolated from blood culture specimen, representing 16 MRSA, 6 methicillin-susceptible S. aureus, 59 methicillin-resistant coagulase- negative staphylococci (MRCNS), and 17 methicillin-susceptible coagulase-negative staphylococci were tested. The isolated colonies from pure culture were directly inoculated onto MSO and MRSAS respectively. On MRSAS any growth appearing pink after 24 hours incubation, and on MSO any growth appearing yellow after 48 hours incubation was interpreted as positive for the presence of MRSA.
RESULTS
Sensitivities of MRSAS and MSO for MRSA detection were equal (93.8%). Specificities for MRSA discrimination from other staphylococci were 98.8% and 89.0%, and especially from MRCNS were 100% and 84.7%, for MRSAS and MSO, respectively.
CONCLUSIONS
The MRSAS showed equal sensitivity compared with MSO for the detection of MRSA. MRSAS showed higher specificity than MSO in discrimination MRSA from MRCNS. It was suggested that the implementation of MRSAS in MRSA screening could decrease the work needed for MRCNS identification.