Methicillin-resistant Staphylococcus aureus detection using chromogenic media: the Sheffield experience

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) continues to cause major problems, both in hospitals and the community. Microbiology departments need to review their methodology regularly to ensure that they are contributing in the most appropriate manner to the battle against MRSA. Media employing chromogenic enzymes to aid the isolation and identification of MRSA is a relatively new approach. In this study, 192 swabs from 112 different patients were inoculated on two chromogen-containing media and four other commonly used solid MRSA media to determine which gave the appropriate combination of sensititivity, specificity and speed of result. Methicillin-resistant S. aureus was isolated on at least one of the six media from 102 of the 192 swabs. Both chromogenic media proved to be statistically significantly more sensitive than the other media after overnight incubation and had a sensitivity of 96% after 48 hours' incubation. The recent introduction of chromogen-containing MRSA media offers microbiology laboratories the opportunity to isolate and confirm the majority of MRSA infections/colonisations in 24 hours, which should result in better patient care. The possible slight increase in costs should not provide a valid excuse for using inferior methodologies.

British Journal of Biomedical Science in 2016. What have we learned?

“…Antibiotic resistance continues to be a major international problem in clinical microbiology, as reflected by the high frequency of scientific research into this topic [38][39][40][41][42][43][44][45]. Although group B Streptococcus species are widely believed to be sensitive to penicillin, a screening method for the possibility of reduced sensitivity (i.e., resistance) has been developed [46].…”

Significantly Larger Numbers of Methicillin-Resistant Staphylococcus aureus Bacteria Are Recovered from Polymicrobial Respiratory and Wound Sites by Use of Chromogenic Primary Media than by Use of Conventional Culture

“…Overall, 192 swabs from wounds, nares, perineum/groin, eye, axilla, and throat were evaluated, with a positivity rate of 53.1% (62 swabs were taken from previously evaluated specimens known to be positive for MRSA) (4). Both chromogenic media had sensitivities of 96% by 48 h, although the extended incubation time did result in some false positives (4). The second study, by Pape et al, found BBL CHROMagar MRSA to be 100% sensitive and specific at 48 h for the isolation of MRSA from 124 positive blood cultures (13).…”

“…Nearly all studies that have evaluated chromogenic media for the detection of MRSA have used surveillance specimens, predominantly from the nares but also including specimens from axilla, groin, rectum, perineum, throat, and wounds (1-3, 7, 8, 10-12, 14, 15), and several studies have found additional reservoirs of MRSA by comparing alternate anatomical sites (1,2,7,11). Comparatively, there have only been two studies that have evaluated the use of chromogenic media for the isolation of MRSA from nonsurveillance clinical specimens (4,13). A British study by Davies et al compared two chromogenic media, MRSASelect agar (Bio-Rad) and CHROMagar MRSA (BioConnections), with four other, nonchromogenic formulations for MRSA detection (4).…”

“…Comparatively, there have only been two studies that have evaluated the use of chromogenic media for the isolation of MRSA from nonsurveillance clinical specimens (4,13). A British study by Davies et al compared two chromogenic media, MRSASelect agar (Bio-Rad) and CHROMagar MRSA (BioConnections), with four other, nonchromogenic formulations for MRSA detection (4). Overall, 192 swabs from wounds, nares, perineum/groin, eye, axilla, and throat were evaluated, with a positivity rate of 53.1% (62 swabs were taken from previously evaluated specimens known to be positive for MRSA) (4).…”