Mannitol salt agar-cefoxitin combination as a screening medium for methicillin-resistant Staphylococcus aureus.
In disk diffusion tests, cefoxitin is now considered a better indicator than oxacillin for the presence of the mecA gene in Staphylococcus aureus. A logical extension of this work is the incorporation of cefoxitin into media selective for methicillin-resistant Staphylococcus aureus (MRSA). This paper describes the development and subsequent testing of mannitol salt agar containing 4 mg/liter cefoxitin with a unique collection of well-characterized MRSA strains, including low-level methicillin-resistant strains and an equal number of known mecA-negative S. aureus strains. The agar supported the growth of 96.6% of the mecA-positive strains in the collection and inhibited the growth of 100% of the mecA-negative strains. These results suggest that selective media based on cefoxitin are superior to those based on oxacillin for the detection of MRSA.
Smyth
R W
RW
Department of Clinical Microbiology, Central Hospital, SE 351 85 Växjö, Sweden. robert.smyth@ltkronoberg.se
Kahlmeter
Gunnar
G
D002440:Cefoxitin / Q000494:pharmacology*; D003470:Culture Media; D008353:Mannitol / Q000494:pharmacology; D016106:Methicillin Resistance; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000254:growth & development
D003470:Culture Media; D008353:Mannitol; D002440:Cefoxitin