Methicillin-resistant Staphylococcus aureus (MRSA) [M201] NEW!

Published: July 8th, 2009

Revised: January 14th, 2010

Staphylococcus aureus is a ubiquitous bacterial colonist of skin surfaces and mucosa in humans. This species is encountered commonly in acne and folliculitis, but also occurs as an agent of wound site infection, catheter-related infection, and deep tissue and organ infections in seriously ill people.

Historically, infections cause by S. aureus were treated successfully with penicillin. However, as a consequence of the widespread use of antibiotics, strains of this bacterium have emerged that resist treatment by penicillins and other drugs. Most common among these strains is so-called Methicillin-resistant Staphylococcus aureus, or MRSA, which occurs commonly in institutions, particularly hospitals and long-term care homes. In these settings, drug resistant strains can spread easily by contact, causing serious illnesses in susceptible people that resist treatment. Surfaces such as door handles, light switches and other surfaces can serve as environmental reservoirs of infectious material. In critical environments, the vigilant cleaning and monitoring of these surfaces is a critical component of an infection control strategy.

In this test, surfaces are sampled using swabs or TefTex wipes, and microbial DNA is isolated directly from the material collected. Dusts can also be sampled. PCR is used to amplify a portion of the gene responsible for methicillin resistance (mecA). The presence of mecA is a proxy for MRSA, and the results of this test are reported qualitatively, as presence/ absence of mecA in the sample. Users are cautioned that because this test uses the presence of a genetic signature of the bacterium, both living and non-living bacteria as well as cell-free bacterial DNA are similarly likely to yield positive test results. Thus, this test can provide a very conservative evaluation for the presence of MRSA, which may provide helpful guidance in public health interventions. As a culture-independent test, results can be available in as little as 4 hr from sample submission, depending on the service option requested. This method cannot distinguish between living and dead cellular material. A negative result does not necessarily refute the presence of potentially infectious material in the area tested, since only a small amount of material is subjected to the test. The testing of multiple replicate samples is helpful to establish confidence on the generalizability of results. A positive result, however, may provide information that is useful in public health interventions.

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