Tehran University of Medical Sciences Acta Medica Iranica 0044-6025 47 4 2009 08 15 329 334 EN Marzieh Aligholi Department of Microbiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Mohammad Emaneini Department of Microbiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Fereshteh Jabalameli Department of Microbiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Shadi Shahsavan Department of Microbiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Zohreh Abdolmaleki Department of Veterinary Pharmacology, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran. Hossein Sedaghat Department of Microbiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Nematollah Jonaidi Health Research Center, Baqiyatallah University of Medical Science, Tehran, Iran. 2015 09 28 Bacterial resistance to antibiotics is a serious problem and is increasing in prevalence world-wide at an alarming rate. The antimicrobial susceptibility patterns of 1897 gram-positive bacterial Isolates were evaluated. The minimum inhibitory concentration (MIC) of isolates which comprised Staphylococcus aureus (927 isolates), coagulase-negative staphylococci (CNS; 425 isolates), Enterococcus faecalis (320 isolates), Enterococcus faecium (157 isolates), and pneumococci (50 isolates) collected from 3 teaching hospitals in Tehran were determined by agar dilution method according to Clinical and Laboratory Standards Institute (CLSI) guidelines. The presence of mecA gene was investigated in methicillin-resistant staphylococci by PCR method and vanA and vanB genes were targeted in enterococcal isolates by Multiplex PCR method. The resistance rate to methicillin among S. aureus and CNS isolates were 33% and 49%, respectively. All S. aureus isolates were susceptible to vancomycin .The lowest rate of resistance in all S. aureus isolates was found for rifampicin (<4%). The vancomycin resistance rate in enterococci isolates was 11% which was more frequent among E. faecium (19%) than E. faecalis (4%), all resistant isolates carrying vanA. High-level resistance to gentamicin and streptomycin, were detected in 47% and 87% of enterococcal isolates respectively. The rate of penicillin resistance in pneumococci was 3% and about 27% of isolates had reduced susceptibility to penicillin. The prevalence of erythromycin resistant among pneumococci was 58%. All pneumococcal isolates were susceptible to ceftriaxone, rifampicin and vancomycin. Our data highlight the importance of access to updated bacterial susceptibility data regarding commonly prescribed agents for clinicians in Iran. https://acta.tums.ac.ir/index.php/acta/article/view/3601 https://acta.tums.ac.ir/index.php/acta/article/download/3601/3577