Colorex™ MRSA is a chromogenic medium for the selective isolation of Methicillin-Resistant Staphylococcus aureus (MRSA). The medium can be used for the routine screening of clinical specimens for MRSA from a variety of sampling sites such as the nose, throat and groin. The medium incorporates a nutritious peptone base medium and a number of selective agents to inhibit most Gram-negative and Gram-positive bacteria as well as yeasts and moulds. The chromogenic detection of specific enzyme activity leads to the formation of pink/mauve colonies indicating MRSA (including low level resistant and hetero-resistant strains) following incubation at 37°C for 18 to 24 hours. Other organisms, if present are indicated by blue or colourless colonies. Any presumptive isolates must be confirmed using serological and/or biochemical techniques available to the laboratory. The use of this chromogenic medium does not diminish the requirement for conventional antimicrobial susceptibility tests for the confirmation of methicillin resistance.
- Storage temperature: 2 to 8°C, store in the dark
- Appearance: firm gel
- Colour: straw
- Recommended incubation: aerobically at 37°C for 16 to 24 hours
- pH: 6.9 ± 0.2
- Plate size: 90mm
- Fill volume: 18 to 22mL
Limitations:
- S. aureus strains that possess a low MIC to the selective agent present in the medium but are mec A negative may form colonies on the medium
- Some MRSA strains may form typical colonies surrounded by a matte halo, the formation of the halo serves no diagnostic function
- Certain methicillin-resistant coagulase-negative staphylococci (CNS) may produce characteristic colonies; in some cases differentiation may be achieved by examination of the colour of these colonies, as they may be considerably darker in colour (bluish purple to a very dark pink/magenta)
- Certain bacterial species other than staphylococci may produce colonies with a characteristic colour
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