[Comparison of the value of disk diffusion methods and polymerase chain reaction for fixation of methicillin...

The detection of methicillin resistance with an appropriate method has a great importance in the treatment of infectious diseases caused by staphylococci. This study was set out to compare disk diffusion method as a phenotypic method, with polymerase chain reaction (PCR), as a genotypic method, for the detection of methicillin resistance in staphylococci. A total of 406 staphylococci strains that were isolated from clinical specimens in microbiology laboratories of adult hospital of Hacettepe University Medical Faculty were included into the study. Of 406 strains, 248 were identified as Staphylococcus aureus, and 158 were coagulase-negative staphylococci (CNS). When the disk diffusion test was compared to PCR for the detection of methicillin resistance, sensitivity and specificity were found as 100% for S. aureus (respectively, 106/106 and 142/142), whereas for CNS sensitivity was 100% (86/86) and specificity was 79% (57/72). For CNS, if zone diameter for resistance was accepted as < or = 14 mm instead of < or = 17 mm, all of the mecA positive strains were found as resistant, whereas three mecA negative strains appeared to be resistant by disk diffusion method [sensitivity: 100% (86/86), specificity: 95.8% (69/72)]. Although disk diffusion was found as a reliable method for the detection of methicillin resistance in S.aureus isolates, it couldn't show the same success in CNS. For that reason in order to obtain the zone diameter for CNS, further studies are needed.