Antimicrobial Resistance Pattern and Minimum Inhibitory Concentration of Vancomycin among Staphylococcus aureus and Coagulase-Negative Staphylococci Isolated from Clinical Specimens of Children in Tabriz

Staphylococci are among common causes of community acquired and nosocomial infections around the world. Over the last decade, the resistance of these bacteria in hospital environments is increasing to various antibiotics such as vancomycin. The aim of present study was to determine the antimicrobial resistance pattern and Minimum Inhibitory Concentration (MIC) values among a clinical collection of staphylococci isolated from hospitalized children in Tabriz. In this prospective and descriptive study, 88 staphylococcal isolates including 53 S. aureus and 35 coagulase-negative staphylococcus species were recovered from various clinical specimens referred to microbiology laboratory of Children Hospital during study period (April 2011 to March 2012). Susceptibility of the isolates against 15 different antimicrobial agents and MIC values of vancomycin was tested using standard disk diffusion and E-test methods respectively. According to the results of drug susceptibility testing, vancomycin and rifampin were the most effective but clindamycin and penicillin were the least effective drugs against tested isolates. Accordingly, the prevalence of methicillin resistant Staphylococcus aureus (MRSA) strains was determined more than 80%. According to MIC values, 13.2% of S. aureus and 3.3% of coagulase-negative staphylococcus isolates showed intermediate resistance to vancomycin. None of the isolates was fully resistant to vancomycin isolates in this study. Although fully vancomycin resistant staphylococci was not found among tested isolates in this study, there was VISA strains. Since there are reports on the emergence of VRSA strains from Iran and other countries, it is necessary for the clinician to care in prescription of vancomycin as a selective drug against staphylococcal infections. Moreover, the necessity of MIC measurement in determining of vancomycin susceptibility is more apparent.