title: Three-way comparison of BBL CHROMagar MRSA II, MRSASelect, and spectra MRSA for detection of methicillin-resistant Staphylococcus aureus isolates in nasal surveillance cultures.
abstract: Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of hospital-acquired and life-threatening infections. Active surveillance programs for MRSA utilize either molecular or culture-based methods. A prospective study was performed to compare the performance of selective and differential chromogenic media, BBL CHROMagar MRSA II (CMRSA II; BD Diagnostics, Sparks, MD), MRSASelect (Bio-Rad Laboratories, Redmond, WA), and Spectra MRSA (Remel, Lenexa, KS), for the detection of MRSA in nasal swab specimens. A total of 515 compliant remnant nasal swab specimens were sequentially used to inoculate BBL Trypticase soy agar with 5% sheep blood (TSA II) and each chromogenic medium. After 24 h of incubation, colony color reactions and morphology on chromogenic media were compared to suspicious colonies on nonselective TSA II. MRSA on TSA II was confirmed by Gram staining, a coagulase test, and a cefoxitin disk test. The overall prevalence of MRSA and methicillin-susceptible S. aureus (MSSA) on TSA II was 12.4% (64/515) and 9.7% (50/515), respectively. When each chromogenic medium was compared to the standard culture method, the sensitivity and specificity, respectively, were as follows: CMRSA II, 87.7% and 98.6%; MRSASelect, 89.0% and 93.4%; and Spectra MRSA, 83.6% and 92.1%. The positive predictive values were highest for CMRSA II (91.4%), followed by MRSASelect (69.1%) and Spectra MRSA (63.5%). False-positive results on chromogenic media were mainly due to color interpretation. The negative predictive values for all three media were greater than 97%. In conclusion, CMRSA II gave the best overall results for detecting MRSA from nasal specimens.
authors.affiliation: Microbiology Laboratory, Indiana University Health Pathology Laboratory, Indianapolis, Indiana, USA. gdenys@iuhealth.org
authors.forename: Gerald A
authors.initials: GA
authors.lastname: Denys
authors.forename: Pamela B
authors.initials: PB
authors.lastname: Renzi
authors.forename: Kim M
authors.initials: KM
authors.lastname: Koch
authors.forename: Carol M
authors.initials: CM
authors.lastname: Wissel
mesh_terms: D001431:Bacteriological Techniques / Q000379:methods*; D002353:Carrier State / Q000175:diagnosis* / Q000382:microbiology; D002863:Chromogenic Compounds / Q000378:metabolism; D003116:Color; D003470:Culture Media / Q000737:chemistry*; D005189:False Positive Reactions; D006801:Humans; D008403:Mass Screening / Q000379:methods; D055624:Methicillin-Resistant Staphylococcus aureus / Q000302:isolation & purification*; D009666:Nose / Q000382:microbiology*; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D013203:Staphylococcal Infections / Q000175:diagnosis* / Q000382:microbiology; D013997:Time Factors
chemical_list: D002863:Chromogenic Compounds; D003470:Culture Media