Background and Aim: MRSA, or methicillin-resistant Staphylococcus aureus, has arisen as a nosocomial and community-acquired infection throughout the world. MRSA identification in the laboratory is difficult for a variety of reasons. The aim of this study was to investigate several phenotypic methods for the detection of MRSA compared with the PCR-based method as the gold standard. Materials and Methods: A total of 220 clinical isolates of S. aureus were recovered from diverse clinical specimens between August 1, 2019 and June 30, 2020 at Milad Hospital in Tehran, Iran. Cefoxitin discs, CHROMagar™,MRSA medium, and identification of the mecA gene by Polymerase Chain Reaction (PCR) as the gold standard method were used to assess methicillin resistance. Results and Conclusion: PCR testing revealed that 105 (47. 72%) of 220 S. aureus isolates were positive for the mecA gene. The results of the Cefoxitin disc diffusion method showed that it has similar sensitivity and specificity to PCR method. The sensitivity and specificity of CHROMagar™,MRSA medium were both 100%. The Cefoxitin disc diffusion method had the same sensitivity and specificity as the PCR method for detecting the mecA gene. For MRSA detection, the Cefoxitin disc diffusion method can be employed as an alternative to PCR.

Background and Objectives: Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of nosocomial and community acquired infections. Detection of MRSA in laboratories is very important for treatment and appropriate infection control. The aim of this study was to evaluate cefoxitin disk diffusion method for detection of MRSA and comparison of this method with other conventional methods. Methods: A total of 175 clinical isolates of S. aureus isolated from clinical specimens were studied. The isolates were identified by conventional laboratory methods. In this respect, E-test MIC, cefoxitin and oxacillin disk diffusion methods, and MAST ID Methicillin strips were used for detection of MRSA. All disk diffusion methods were performed as recommended by NCCL and manufacturers’ guidelines. Results: Using E-test MIC, 53 out of 175 strains of S. aureus were resistant to methicillin. In addition, disk diffusion method using oxacillin disk showed that 52 strains are resistant to methicillin. In this respect, 8 strains had intermediate resistance to methicillin. For cefoxitin disk diffusion method, 52 strains were resistant to methicillin. This method had a good correlation with E-test MIC method. Meanwhile, MAST ID methicillin strips detected 47 strains that were resistant to mehicillin. Sensitivity and specificity for both cefoxitin and oxacillin disk diffusion methods were 98%and 100% respectively. However cefoxitin was better than oxacillin for detecting intermediate resistant strains of S. aureus. Sensitivity and specificity for MAST ID methicillin strips were 91% and 100% respectively. Conclusion: This study revealed that cefoxitin disk diffusion method is a good alternative for oxacillin disk diffusion method for detection of MRSA. This method is more reliable for identification of intermediate resistant strains of S. aureus.

Background: Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most important pathogen in the hospital and community. Therefore, a precise identification of the antibiotic-resistant strains is essential to control the infection and prevent the MRSA transmission rates. The aim of this study was to determine a diagnostic value of cefoxitin susceptibility test compared with the oxacillin susceptibility test and E-test (Epsilometer test) for detection of MRSA.Materials and Methods: This study was conducted on 296 S.aureus isolated from the nasal specimen patients of referred to emergency department of Kashsn Shahid-Beheshti hospital.Resistance to methicillin was determined by oxacillin (1mg), and cefoxitin (30mg) disk diffusion methods based on CLSI guideline and according to no growth zone size and the minimum inhibitory antibiotic concentration by E-test. PCR assay was used as a gold standard for detecting mecA gene in MRSA isolates.Results: Thirty-two (10.8%), 28 (9.5%), 30 (10.1%), 26 (8.8%) out of 296 S.aureus were considered as MRSA strains using the oxacillin and cefoxitin disk diffusion methods, E-test and PCR, respectively. Sensitivity, specificity, positive and negative predictive values for the oxacillin diffusion method were 100%, 97.7%, 81.2% and 100%; for the cefoxitin disk diffusion method 96.2%, 98.8%, 89.3% and 99.6% and for E-test 100%, 98.5%, 86.7% and 100%, respectively.Conclusion: PCR assay is the best method for detecting MRSA; however, it is an expensive method. Phenotypic methods, especially the cefoxitin disk diffusion method, can be a good alternative to PCR for detection of MRSA.

Staphylococcus aureus are Gram positive bacteria known to acquire antibiotic resistance rapidly and pose a major challenge to clinicians worldwide. Infections by methicillin resistant Staphylococcus aureus (MRSA) are usually associated with increased mortality and prolonging of treatment. Samples (n = 706) from diverse sources (livestock, pets, animal handlers, human hospital) were collected and screened for the presence of MRSA by phenotypic and genotypic methods. The incidence of Staphylococcus aureus was greater in goats (42.00%; 28.20 - 56.80%, confidence interval [CI] 95.00%) followed by cattle (13.50%; 9.20 - 18.80%, CI 95.00%), humans (12.90%; 9.30 - 17.40%, CI 95.00%) and dogs (12.90%; 8.10 - 19.20%, CI 95.00%). Significantly higher incidence of MRSA was observed in dogs (65.00%; 40.80 - 84.60%, CI 95.00%), compared to other hosts namely cattle (48.00%; 26.50 - 64.30%, CI 95.00%), humans (35.00%; 20.20 - 52.50%, CI 95.00%) and goats (10.00%; 1.20 - 30.40%, CI 95.00%). All the S. aureus isolates were further screened for thermostable nuclease (nuc gene) by polymerase chain reaction (PCR). The incidence of nuc gene in cattle, dog, goat and human were found to be 3.30% (1.30 - 6.60%, CI 95.00%), 5.20% (2.30 - 9.90%, CI 95.00%), 28.00% (16.20 - 42.50%, CI 95.00%) and 9.10% (6.00 - 13.00%, CI 95.00%), respectively. Comparative evaluation of two PCR primers (mecA-162 and mecA-310) indicated the former one as more rational choice for detection of MRSA. Overall, the results of our study indicated possible risk of zoonotic transmission of MRSA from canines.

Background and Objective: Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most common microorganisms that is recovered from clinical bacterial isolates. Clinical and Laboratory Standards Institute (CLSI) recommends usage of cefoxitin when using the disk diffusion method to determine resistance against methicillin for S. aureus. The aim of our study was to evaluate the efficacy of cefoxitin disk diffusion test to detect MRSA and compare it with PCR methods for detection of mecA gene.Materials and Methods: S. aureus was isolated from patients in five selected hospitals of Tehran province and identified by biochemical conventional methods and PCR for nuc gene (specific for this bacterium). Cefoxitin disc diffusion test was performed using 30 mg disc according to recommendations of CLSI. PCR for amplification of the mecA gene was performed.Results: With phenotypic methods and PCR for nuc gene, identification of 101 isolates was confirmed as S. aureus. Disk diffusion method showed that all isolates were susceptible to vancomycin and linezolid antibiotics and 58 isolates were found to be methicillin resistant by cefoxitin disc diffusion. For these 58 isolates, mecA gene was positive.Conclusion: In the absence of availability of molecular biology techniques, the cefoxitin disc can be an alternative to PCR for detection of MRSA as a simple and economically low cost method.