Cefoxitin disc diffusion test for detection of meticillin-resistant staphylococci.

Staphylococci are the main causative agents of nosocomial diseases. Over the last few years, the increase in the number of meticillin-resistant (MR) staphylococci has become a major clinical problem. Accuracy and promptness in the detection of meticillin resistance are of key importance in ensuring the correct antibiotic treatment in infected patients and control of MR staphylococci in the hospital environment. This study evaluated the accuracy of a cefoxitin disc diffusion (DD) test for the detection of meticillin resistance in staphylococci. A total of 144 clinical isolates [97 Staphylococcus aureus and 47 coagulase-negative staphylococci (CoNS)] were tested using a mecA gene PCR, a DD test (oxacillin, 1 mug disc; cefoxitin, 30 mug disc), determination of oxacillin MIC by agar dilution (AD), and an oxacillin screen agar test at oxacillin concentrations of 4 and 6 mug ml(-1). Of the 97 S. aureus and 47 CoNS isolates, 73 (75.26 %) and 30 (63.83 %), respectively, were mecA-positive. The sensitivity and specificity of the cefoxitin DD test were 94.44 and 95.83 %, respectively, for S. aureus and 80 and 100 %, respectively, for CoNS. The oxacillin DD method was 100 % sensitive and 58.33 % specific for S. aureus, and 86.67 % sensitive and 70.59 % specific for CoNS. The AD test was highly sensitive (98.63 %) and specific (98.53 %) for S. aureus and CoNS (83.33 % sensitive and 94.12 % specific). The cefoxitin DD test for meticillin-resistance detection was more specific but less sensitive than the oxacillin DD test. Use of DD tests for both cefoxitin and oxacillin can help in more accurate prediction of meticillin resistance. Centres that are not equipped to carry out PCR can use AD methods for confirmation of meticillin resistance, especially in oxacillin-resistant and cefoxitin-sensitive cases.