Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 13 4 2021 08 11 442 448 Negin Abdizadeh Department of Animal Biology, Faculty of Natural Sciences, University of Tabriz, Tabriz, Iran Mehri Haeili Department of Animal Biology, Faculty of Natural Sciences, University of Tabriz, Tabriz, Iran Hossein Samadi Kafil Drug Applied Research Center, Tabriz University of Medical Sciences, Tabriz, Iran Amin Ahmadi Pharmaceutical Nanotechnology Research Center, Biomedicine Institute, Tabriz University of Medical Sciences, Tabriz, Iran Mohammad Mehdi Feizabadi Department of Microbiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran; Thoracic Research Center, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran 2021 01 31 2021 06 25 Background and Objectives: Ceftaroline (CPT) is a novel cephalosporin with potent activity against methicillin-resistant Staphylococcus aureus (MRSA). Despite its recent introduction, CPT resistance in MRSA has been described worldwide. We aimed in the current study to evaluate the in vitro activity of CPT against 91 clinical MRSA and 3 MSSA isolates. Materials and Methods: Susceptibility of isolates to CPT was tested using E-test and disk diffusion (DD) method. The nucleotide sequence of the mecA gene and molecular types of isolates with reduced susceptibility to CPT were further studied to identify resistance conferring mutations in PBP2a and the genetic relatedness of the isolates respectively. Results: Overall, 92.5% of isolates were found to be CPT susceptible (MICs≤1mg/l) and 7 MRSA isolates were characterized with MIC=2mg/l and categorized as susceptible dose dependent. Compared to E-test, DD revealed a categorical agreement rate of 93.6% and the obtained rates for minor, major /very major error were found to be 6.3% and 0% respectively. The MRSA isolates with increased CPT MICs (n=7), belonged to spa types t030 (n=6) and t13927 (n=1) and all carried N146K substitution in PBP2a allosteric domain, except for one isolate which harbored a wild-type PBP2a. Conclusion: While resistance to CPT was not detected we found increased CPT MICs in 7.69% of MRSA isolates. Reduced susceptibility to CPT in the absence of mecA mutations is indicative of contribution of secondary chromosomal mutations in resistance development. https://ijm.tums.ac.ir/index.php/ijm/article/view/2965 https://ijm.tums.ac.ir/index.php/ijm/article/download/2965/1364