Journal of Pure and Applied MicrobiologyVol. 7 No. 4

Evaluation of Phenotypic Versus Genotypic Methods Commonly used in the Detection of Oxacillin Resistance in Staphylococcus aureus

Mounir M. Salem- Bekhit1,2 and Sherif H. Abd-Alrahman3,4

1Department of Pharmaceutics, College of Pharmacy, King Saud University, P. O. Box 2457, Riyadh, Saudi Arabia. 2Department of Microbiology and Immunology, Faculty of Pharmacy, Al-Azhar University, Cairo, Egypt. 3Biochemistry Department, College of Science, King Saud University, Riyadh, Saudi Arabia. 4Pesticides Residue and Environmental Pollution Department, Central Agricultural Pesticide Laboratory, Agricultural Research Center, Giza 12618, Egypt.

Received on 06 July 2013 and accepted on 03 September 2013



Accurate and early detection of methicillin-resistant S.aureus (MRSA) is great important for the management of infected patients and select the appropriate infection control measures. Accordingly, evaluation of the accuracy of the phenotypic and genotypic methods commonly used to determine the profile of antimicrobial resistance is essential to ensure that the most appropriate therapy is chosen. Two hundred and twenty eight strains of Staphylococcus sp. (106 S. aureus and 122 coagulase negative Staphylococcus sp.) were used to assess the accuracy of the methods of disk diffusion, oxacillin screening agar and agar microdilution, in comparison with polymerase chain reaction (PCR) for exploring resistance to oxacillin. The mecA gene was detected in 31 strains (20.7%), and 29 strains (19.3%) showed discrepant results in at least one of the methods. For S. aureus, all the methods showed 100% specificity and sensitivity except for the automated Microscan WalkAway, which showed 92.9% sensitivity and 85%. In relation to coagulase negative Staphylococcus sp, the cefoxitin disk had lower accuracy (85% sensitivity). Use of two methods should be the best option for improved sensitivity, offer a time-saving and accurate method of detection of oxacillin resistance in S. aureus.

Keywords : Staphylococcus aureus, mecA, MRSA, Oxacillin, Cefoxitin.