Mrsa Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Mrsa and links to relevant pages within the course.
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|Methicillin-Resistant Staphylococcus aureus (MRSA) Screen|
Perhaps the most efficient means for detecting methicillin-resistant staphylococci in clinical laboratories is the use of the agar dilution screening test. Illustrated in the image is a Mueller-Hinton agar plate containing 6 ug/mL of oxicillin, previously inoculated with a strain of Staphylococcus aureus. Oxacillin is used as a marker for methicillin resistance because it is more stable in the agar medium. Growth on this screening medium is presumptive for methicillin resistance. Thus, in the presence of growth, as shown here, a follow-up minimum inhibitory concentration (MIC) test must be performed to determine the exact level of resistance.
|Methicillin-Resistant Staphylococcus aureus (MRSA) Disk Test|
The disk diffusion test can also be used in the detection of methicillin-resistant Staphylococcus aureus. Illustrated in the image is the surface of a Mueller-Hinton agar plate previously inoculated with a strain of S. aureus suspected of being methicillin-resistant. Although the zone of inhibition is at the borderline for resistance (18 mm); the presence of small colonies within the zone of inhibition (yellow arrows) indicates the presence of heteroresistant strains. The interpretation here, therefore, is "methicillin-resistant" staphylococci, even though the zone diameter appears to be adequate. The detection of the heteroresistant strains indicates that minimum inhibitory concentration (MIC) studies are required.
Hershow RC. Khayr WF. Smith NL.: A comparison of clinical virulence of nosocomially acquired methicillin-resistant and methicillin-sensitive Staphylococcus aureus infections in a university hospital (University of Illinois at Chicago). Infection Control & Hospital Epidemiology. 13(10):587-93, 1992 OBJECTIVES: To compare the clinical virulence of nosocomially acquired methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) infections in 1989. DESIGN: A retrospective comparison of host factors, in-hospital exposures, sites of infections, and outcomes of patients with nosocomial MRSA and MSSA infections. PARTICIPANTS: Forty-four adult patients with nosocomial S.aureus infections. RESULTS: The 22 MRSA-infected and 22 MSSA-infected persons were similar regarding mean age, gender, underlying diseases, and exposure to surgery. Before developing infection, MRSA-infected persons were more likely to have received antibiotics and to have stayed in the hospital > 2 weeks. Bacteremia was the most common presentation in the MRSA and MSSA groups (55% and 59%, respectively). Infectious complications and death were infrequent in both groups. CONCLUSIONS: MRSA and MSSA strains infect patients with similar demographic features and underlying diseases, but MRSA infections are significantly more common among patients with previous antibiotic therapy and a prolonged preinfection hospital stay. Clinical presentations and outcomes did not differ significantly between the 2 groups. Thus, similar to studies in the early 1980s, our findings do not suggest greater intrinsic virulence of MRSA.
|Factors predisposing to infections with methicillin resistant Staphylococcus aureus (MRSA) include: (choose all that apply)||View Page|
|Patients with infections with MRSA have uniformly poorer outcomes than those infected with sensitive strains.||View Page|