Mrsa Community

Sean Naughton
C09383352
Medical Microbiology

Introduction

A 46 year old male general practitioner presented with facial abscesses. The patient’s wife suffered from similar skin abscesses. Swabs were taken and MRSA was isolated. Based on the sensitivity patterns the consultant microbiologist suspected that it was a community acquired strain, and requested that the isolate be sent to the National MRSA Reference Laboratory.

Overview and Clinical significance

MRSA is a strain of Staph Aureus which does not respond to treatment from antibiotic drugs such as cefoxitin and methicillin (1), (2). This is generally associated as an organism which colonises patients in a hospital setting. It can cause infections from soft tissue infections to sepsis, pneumonia, tissue damage and necrosis. Community acquired MRSA is not just a hospital acquired strain that has escaped into the community. The genes encoding methicillin resistance in these organisms reside on different genetic residues to those of hospital acquired strains (3).CA-MRSA can have different traits causing the infections and typing of MRSA organisms can be done to detect if it is hospital or community acquired.



Isolation

The swab was received by the lab in an Amies transport medium which contains charcoal. The swab was inoculated onto Blood agar, and Uriselect and Neomycin blood. Blood agar is a non-selective medium which supports growth of most organisms. It requires and incubation period of 24-48 hours in air at 37 C. Uriselect is a differential chromogenic media that differentiates between organisms such as e.coli, coliforms and pseudomonads These organisms react differently with enzymes in the agar and produce a different colour. The Neomycin 75mg/L agar was incubated with a Metronidazole disc at 37 C, in anaerobic conditions for 48 hours. Any anaerobes growing on this plate will be susceptible to the Metronidazole disc. A gram stain was also performed and Gram positive cocci in clusters...