Antibiotic Susceptibility Pattern of Gram-positive Cocci Cultured from

Abstract- 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 re-sistance 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 peni