COMPARISON OF SCREENING METHODS TO IDENTIFY METHICILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS

Screening methods to identify methicillin-resistant Staphylococcus aur eus (MRSA) were compared using 96 isolates representing 17 distinct cl ones. The sensitivity of four commercial agglutination tests was deter mined in comparison to the tube coagulation test, and the results rela ted to the presence of the coagulase gene, The broth screening test, a gar dilution test and disc diffusion test were carried out, and the re sults related to the presence of the mecA gene, Mannitol salt agar and Iso-Sensitest agar with varying salt supplements were used, All agglu tination tests had high rates of detection of Staphylococcus aureus (9 5.8-99.0%). Resistance in mecA gene-positive Staphylococcus aureus iso lates was correctly detected by the oxacillin broth test, the agar dil ution test and the disc diffusion test on mannitol salt agar, whereas on Iso-Sensitest agar detection rates were lower (between 68.5% and 94 .4%, depending on the salt supplement), Incubation of the Iso-Sensites t plates for 48 hours significantly improved the rate of detection of resistance, but increased the major error rate up to 71.4%, MecA gene- positive Staphylococcus aureus isolates not detected by the disc diffu sion test on Iso-Sensitest agar had significantly lower oxacillin mini mal inhibitory concentration values and were significantly less resist ant to a variety of antibiotics, Thus, mannitol salt agar might be a s uitable medium for use in the disc diffusion and agar dilution test to detect resistance to oxacillin in Staphylococcus aureus.