IOSR Journal of Pharmacy and Biological Sciences (IOSR-JPBS) ISSN: 2278-3008. Volume 4, Issue 6 (Jan. – Feb. 2013), PP 37-40 www.iosrjournals.org www.iosrjournals.org 37 | Page Antibiotic Resistance Pattern of Methicillin Resistant Staphylococcus aureus Isolated From Clinical Specimens Salah Uddin Khan 1 , Mahmood Ahmed Chowdhury 2 , Md. Abdul Hakim 3 1 Department of Microbiology, University of Chittagong , Bangladesh 2 Department of Microbiology, Chattagram Maa Shishu O General Hospital, Chittagong, Bangladesh 3 Department of Microbiology, University of Chittagong , Bangladesh Abstract: Methicillin Resistant S. aureus poses serious threat to human health since the mortality and morbidity rate due to S. aureus infection is significant. In the present study, a total of 37 S. aureus strains isolated from 1078 clinical were tested against various antibiotics. Antibiotic susceptibility of the isolated S. aureus was carried out using disk diffusion method. The MIC and MBC of different antibiotics were determined by tube dilution assay and disk diffusion technique. The maximum prescribed antibiotic groups were cephalosporins and penicillins. The most resistant group was penicillin followed by aminoglycoside, cephalosporins and quinolones. The order of resistance of S. aureus against various antibiotics was ampicillin (92.10%), cloxacillin (61.29%), cefradine (60%), ciprofloxacin (59.35%), gentamicin (58.06%). There was no resistant isolate against vancomycin; however, four isolates (10.52%) had shown intermediate sensitivity. MIC and MBC of five major groups of antibiotics namely, penicillins, cephalosporins, aminoglycosides, quinolones and vancomycin were also determined. In-vitro study of MBC of the five groups of antibiotics showed 2 to 3 fold two-fold dilution higher value than in MIC of each group of antibiotic. Only MBC of vancomycin was in the range of 1 to 2 two-fold dilutions higher than their MICs. Keywords - Antibiotic resistance, MRSA, MIC, MBC, Staphylococcus aureus I. Introduction Multidrug resistance is now a very common norm in S. aureus. The mortality of S. aureus bacteremia remains approximately 20–40% despite the availability of effective antimicrobials, which indicates the propensity of S. aureus to develop resistance. Some strains that infect hospitalized patients are resistant to most of the antibiotics used to treat infections, vancomycin being the only remaining drug to which resistance has not developed [1]. There are also reports of MRSA strains with less susceptibility toward Vancomycin [2]. Some identified genes to be the cause of such resistance. Staphylococcus cassette chromosome mec, encodes methicillin resistance in Staphylococcus aureus [3]. S. aureus resistance to penicillin is mediated by blaZ, the gene that encodes β-lactamase. Methicillin resistance requires the presence of the chromosomally localized mecA gene. The cause behind the resistance of quinolones to be the stepwise acquisition of chromosomal mutations. Vancomycin resistance has resulted from the probable conjugal transfer of the vanA operon from a vancomycin-resistant E. faecalis [4] . The study was thus conducted to observe the pattern of antibiotic resistance of S. aureus isolated from clinical samples. II. Material and Methods A total of 1078 samples received in the microbiology laboratory of Chattagram Maa Shishu O General Hospital, which include blood, pus and miscellaneous samples (swabs/sputum/body fluids). 2.1 Sample Processing 2.1.1 Blood Blood samples were collected from patients visiting OPD (Out Patients Department), different wards (IDP) and were brought to the pathology laboratory. Freshly drawn, 3-5 mL blood was immediately transferred to 50 mL of Tryptone Soya broth (CM0129-OXOID), and incubated at 37 o C for 24 hours. Then sub-cultured on Blood Agar (CM 0055- OXOID), Chocolate agar (by heating Blood Agar at 63 o C) and MacConkey Agar (CM 0007-OXOID) plates, and incubated for 24 hours at 37 o C. 2.1.2 Pus Pus samples were plated directly onto Blood Agar (CM 0055- OXOID), Chocolate agar (by heating Blood Agar at 63 o C) and MacConkey Agar (CM 0007-OXOID), and incubated for 24 hours at 37 o C.