Spectra MRSA, a new chromogenic agar medium to screen for methicillin-resistant Staphylococcus aureus.
A novel chromogenic medium, Spectra MRSA (Remel, Lenexa, KS), was designed to detect methicillin-resistant Staphylococcus aureus (MRSA) rapidly and more efficiently than traditional media (i.e., tryptic soy agar with 5% sheep blood [SBA] and mannitol salt agar [MSA]). A multicenter study (including four clinical trial sites and the Medical College of Wisconsin [MCW] Milwaukee, WI) compared the performance characteristics of Spectra MRSA to those of the traditional media for the detection of MRSA. For this study, 767 nasal swab specimens from the multicenter study (traditional medium used, SBA) and 667 nasal swab specimens from MCW (traditional medium used, MSA) were plated on each test medium and examined after 24 and 48 h of incubation. At 24 h, the sensitivity and the specificity of each medium were as follows: in the multicenter study, 95.4% and 99.7%, respectively, for Spectra MRSA and 93.6% and 100%, respectively, for SBA; at MCW, 95.2% and 99.5%, respectively, for Spectra MRSA and 88.7% and 94.0%, respectively, for MSA. The positive predictive values of each medium at 24 h were as follows: in the multicenter study, 98.1% for Spectra MRSA and 100% for SBA; at MCW, 95.2% for Spectra MRSA and 60.4% for MSA. In our evaluation, we found that Spectra MRSA was able to rapidly identify and differentiate methicillin-resistant S. aureus from methicillin-susceptible S. aureus on the basis of the utilization of chromogens that result in denim blue colonies, thus eliminating the need for biochemical analysis and antimicrobial susceptibility testing. Extending the incubation beyond 24 h did not significantly improve the recovery of MRSA and resulted in decreased specificity.
Peterson
Jess F
JF
Department of Pathology, Medical College of Wisconsin, 9200 West Wisconsin Ave., Milwaukee, WI 53226, USA.
Riebe
Katherine M
KM
Hall
Gerri S
GS
Wilson
Deborah
D
Whittier
Susan
S
Palavecino
Elizabeth
E
Ledeboer
Nathan A
NA
D000362:Agar; D001431:Bacteriological Techniques / Q000379:methods*; D002863:Chromogenic Compounds / Q000378:metabolism; D003116:Color; D003470:Culture Media / Q000737:chemistry*; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000302:isolation & purification* / Q000378:metabolism; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity; D013203:Staphylococcal Infections / Q000175:diagnosis* / Q000382:microbiology
D002863:Chromogenic Compounds; D003470:Culture Media; D000362:Agar