Evaluation of Brilliance MRSA 2 Agar for Detection of Methicillin-Resistant Staphylococcus aureus in Clinical Samples

Abstract

We compared 2 chromogenic media (Oxoid Brilliance MRSA 2 agar [Thermo Fisher Scientific] and MRSA-ID [bioMérieux]) for the detection of methicillin-resistant Staphylococcus aureus (MRSA) in 1,368 hospital samples. For both media, broth enrichment was essential to obtain satisfactory diagnostic performance. Although with direct cultures only, the diagnostic performance (particularly sensitivity) of Brilliance MRSA 2 agar appears better than that of MRSA-ID, no difference in sensitivity or specificity between the media was detected after inclusion of an enrichment step. R apid and accurate screening of patients for methicillin-resistant Staphylococcus aureus (MRSA) is essential to control MRSA in hospitals. Several chromogenic selective media have been developed to facilitate such screening. We previously compared the diagnostic performances of two of these media, Brilliance MRSA agar (Thermo Fisher Scientific) and MRSA-ID (bioMérieux, France), for the detection of MRSA in nose and throat samples taken from veterinarians and their household members (1). Although sensitivities were high and similar for both media, the specificity of the Brilliance MRSA agar (88.7%) was substantially less than that of MRSA-ID (98.5%). Since then, the manufacturer of the Brilliance MRSA agar has redeveloped the medium to improve its accuracy, particularly the specificity, which would reduce the number of confirmatory tests required. In the current study, we compared the performances of the new Brilliance MRSA 2 agar and MRSA-ID for the detection of MRSA.The study was conducted in the Laboratory for Microbiology and Infection Control in Amphia Hospital, Breda, The Netherlands. In this laboratory, the MRSA-ID medium was used for the routine screening for MRSA, and the Brilliance MRSA 2 agar was included as a comparator for this study. The composition of each chromogenic medium is proprietary. The selective mixture inhibits the growth of methicillin-sensitive staphylococci and most other bacteria and yeasts. Contrary to MRSA-ID medium, the performance of Brilliance MRSA 2 agar is not affected by light exposure, which is a practical advantage in its use. On Brilliance MRSA 2 agar, MRSA forms distinctive blue colonies, while such colonies on the MRSA-ID medium are green.Rectal, throat, and nose swabs were collected between December 2011 and July 2012 using the ESwab transport medium (Copan Diagnostics). ESwab containers were vortexed, and swabs were used to inoculate both MRSA-ID agar and Brilliance MRSA 2 agar plates and a Columbia agar plate with 5% sheep blood (SBA growth control). The order in which samples were inoculated on the 2 chromogenic media was alternated weekly. The fluid remaining from the ESwab container (500 to 1,000 l) was inoculated in Mueller-Hinton broth (6.5% NaCl) that was subcultured after 18 to 24 h of incubation at 36 to 37°C in normal atmosphere on both chromogenic media and on a Columbia agar plate with 5% sheep blood (SBA). The latter was included as a backup to detect the presence of MRSA strains that would r...

Evaluation of two commercially available chromogenic media for confirmation of methicillin-resistant Staphylococcus aureus from human, animal, and food samples

“…These results are similar to those obtained previously in human clinical samples (McElhinney et al, 2013;Veenemans et al, 2013). However, a significantly lower performance was observed in the MRSA confirmation of food-derived isolates by using Brilliance MRSA 2 agar in comparison to PCR-based MRSA confirmation (p = 0.003) or ChromID MRSA agar Table 1 Comparative diagnostic performance of Brilliance MRSA 2 Agar and ChromID MRSA agar for detection of animal, human and food isolates of methicillin-resistant Staphylococcus aureus.…”

“…Several commercially available chromogenic media have been developed to facilitate the screening of MRSA, and some studies have assessed their diagnostic performance (McElhinney et al, 2013;Veenemans et al, 2013;Verkade et al, 2011). However, they have been mainly focused in human clinical samples, and there is a knowledge gap regarding MRSA from animal and food samples.…”

Prospective Two-Center Comparison of Three Chromogenic Agars for Methicillin-Resistant Staphylococcus aureus Screening in Hospitalized Patients

“…The sensitivity of the SMART agar was statistically significantly higher at 24 h than that with chromID, but no difference in sensitivity between the SMART and OX2 agars was observed. However, 30 (29.7%) of MRSA isolates detected in the present study would have been missed by the SMART agar if screening samples had been inspected only at 18 to 24 h. As previously reported, an EB step increases the yield for MRSA detection, which is also the case for the new SMART agar (8,10,15). A difference in the specificity of the SMART agar plates was noted between the two study sites at 48 h of incubation.…”

“…Several chromogenic agars have been specifically developed for MRSA screening. These media show superior sensitivity and specificity compared to those of conventional selective plates (8)(9)(10). The purpose of this study was to compare the performance of the new bioMérieux chromID MRSA SMART (SMART) agar with bioMérieux chromID MRSA first generation (chromID) and Oxoid Brilliance MRSA version 2 agar (OX2) with and without enrichment broth (EB).…”

Large Outbreak Caused by Methicillin Resistant Staphylococcus pseudintermedius ST71 in a Finnish Veterinary Teaching Hospital – From Outbreak Control to Outbreak Prevention

“…Some degree of misclassification may have occurred due to the imperfect sensitivity of the MRSP screening method. Studies have reported the sensitivity of similar methods for MRSA in humans or livestock to be up to 98% [25] – [28] . Comparable methods have been used for MRSP detection in at least two studies [29] , [30] , but currently no reference standard for the screening of MRSP exists.…”