Background and
Objectives:
Phenotypic
methods for
detection of
methicillin resistant Staphylococcus aureus (
MRSA) have been compared with the
gold standard which, as of now, is by the
detection of mecA
gene and femA
gene by
polymerase chain reaction (
PCR). Discrepancies in
detection have an adverse effect on
patient management, thereby highlighting the importance of accuracy in
detection. Our study aims to evaluate the
efficacy of
cefoxitin disk
diffusion test to detect
MRSA and compare it with other phenotypic and molecular
methods.
Methodology; The study was conducted from June 2006 to December 2007 and included 610
Staphylococcus aureus (S. aureus) isolates obtained from clinical samples. All isolates were tested for
MRSA using
oxacillin screen
agar plates with 6 µg/ml of
oxacillin,
cefoxitin disk
diffusion using 30 µg disk and MIC of
oxacillin. Selected isolates (55) were tested for presence of mecA
gene and Fem
A gene by
PCR.
Results:
Out of 610 isolates,
MRSA was identified in 34.09% by
cefoxitin disk
diffusion, 34.9% by
oxacillin screen
agar, 34.4% by MIC and 37.3% by
oxacillin disk
diffusion. When selected isolates were tested with molecular
methods, the
cefoxitin disk
diffusion and
PCR tests were comparable.
Discussion:
Prevalence of
MRSA (34.09%) is quite high as in other studies. The
oxacillin disk
diffusion test which was used routinely earlier is showing low
specificity (56%). Among all phenotypic
methods,
cefoxitin disk
diffusion and
PCR alone have
similar sensitivity and specificity.
Conclusion:
Results of
cefoxitin disk
diffusion test are in concordance with the
PCR for mecA
gene. Thus, the test can be an alternative to
PCR for
detection of
MRSA in
resource constraint settings.