Multicenter Evaluation of BBL CHROMagar MRSA Medium for Direct Detection of Methicillin-Resistant Staphylococcus aureus from Surveillance Cultures of the Anterior Nares

Abstract

Active surveillance for methicillin-resistant Staphylococcus aureus (MRSA) is among the strategies recommended by the Society for Healthcare Epidemiology of America for control of nosocomial MRSA infections. Infection control and laboratory personnel desire rapid, sensitive, and inexpensive methods to enhance surveillance activities. A multicenter study was performed to evaluate a new selective and differential chromogenic medium, BBL CHROMagar MRSA (C-MRSA) medium (BD Diagnostics, Sparks, MD), which enables recovery and concomitant identification of MRSA strains directly from nasal swab specimens taken from the anterior nares. Specimens were inoculated to C-MRSA and Trypticase soy agar with 5% sheep blood agar (TSA II, BD Diagnostics). Mauve colonies on C-MRSA at 24 h and 48 h and suspicious colonies on TSA II were confirmed as Staphylococcus aureus by Gram stain morphology and a coagulase test. In addition, the results of C-MRSA were compared to results of susceptibility testing (five different methods) of S. aureus strains isolated on TSA II. A total of 2,015 specimens were inoculated to C-MRSA and TSA II. Three hundred fifty-four S. aureus isolates were recovered; 208 (59%) were oxacillin (methicillin) susceptible and 146 (41%) were oxacillin resistant (MRSA). On C-MRSA, 139/146 or 95.2% of MRSA isolates were recovered, whereas recovery on TSA II was 86.9% (127/146) (P ‫؍‬ 0.0027). The overall specificity of C-MRSA was 99.7%. When C-MRSA was compared to each susceptibility testing method, the sensitivity and specificity, respectively, were as follows: oxacillin MIC by broth microdilution, 94.4% and 96.7%; oxacillin screen agar, 94.3% and 96.7%; PBP2 latex agglutination, 93.7% and 98.5%; cefoxitin disk diffusion, 95.0% and 98.1%; and mecA PCR, 95.1% and 98.1%. In this study, C-MRSA was superior to TSA II for recovery of MRSA from surveillance specimens obtained from the anterior nares and was comparable to conventional, rapid, and molecular susceptibility methods for the identification of MRSA isolates.

Cloth-covered chiropractic treatment tables as a source of allergens and pathogenic microbes

“…For instance, S aureus is now suspected to be present in up to 40% of patients' anterior nares; and close to 1% of people may carry MRSA strains. 10 Seasonally, many viral pathogens come to mind, including influenza. Currently, the chiropractic profession in the United States does not have a suggested guideline that it has adopted for disinfecting of treatment tables, although there are available models in the literature.…”

A Preoperative Decolonization Protocol for Staphylococcus aureus Prevents Orthopaedic Infections

“…Mauve colonies present on either medium at 48 hours were verified as S. aureus by Gram's stain and coagulase testing (Staphaurex, Remel, Lenexa, Kansas). Mauve colonies growing on both media were reported as MRSA while colonies growing only on CHROMagar SA were reported as MSSA [3,4].…”

Changing epidemiology of methicillin-resistantStaphylococcus aureuscolonization in paediatric intensive-care units

“…Cultures were processed using standard microbiological methods [31]. [32], and isolates with inducible clindamycin resistance were reported as clindamycin resistant.…”