AbstractBackground: Carbapenemase-resistant Enterobacteriaceae is a major threat to public health. These microorganisms are resistant to all types of beta-lactam antibiotics.Methods: This cross-sectional study was conducted on 51 Enterobacteriaceae isolates from clinical samples in Sina Hospital and Tehran Heart Center in Iran from 2016 to 2018. Antibiotic susceptibility test was performed by disk diffusion method. Carbapenem-resistant isolates were identified by the Modified Hodge Test (MHT) and Polymerase Chain Reaction (PCR) for surveying the presence of VIM, NDM, IMMP, and OXA-48 genes.Results: Out of 51 clinical samples, 38 isolates were positive for both MHT and PCR tests, and 5 isolates were negative in both tests. The results of both tests are similar in 84.3% of the isolates.Conclusion: The MHT is an appropriate and easy method for approving carbapenemase production. Also, a laboratory can detect the carbapenemase production by identification of the KPC genes.

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 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 Objective: Resistance of Staphylococcus aureus to antibiotics is one of the major global health problems in human societies. Thus, evaluation of pattern of antibiotic resistance in its different strains is very important. This study was carried out to evaluate the antibiotic resistance in Staphylococcus aureus isolated from clinical samples by disk diffusion and PCR methods.Methods: In this laboratory- descriptive study, 50 isolates of Staphylococcus aureus to be identified from clinical specimens. Methicillin resistance was examined using PCR and antibiotic susceptibility of isolates was tested by disk diffusion method.Results: 50 isolates were resistant to methicillin, ampicillin and penicillin. The resistance of isolates to erythromycin, Gentamicin, Clindamycin and Ciprofloxacin were 48%, 34%, 34%, 34%, respectively. The PCR method showed that 98% of Methicillin Resistance of Staphylococcus aureus isolates carried the methicillin resistant gene.Conclusion: This study indicated that 98% isolates harbor mecA genes and more resistant to methicillin related mecA genes.