Investigation of reduced vancomycin susceptibility in methicillin-resistant staphylococci

Staphylococci are among the most important aetiological agent of nosocomial and community-acquired infections, although found in human normal flora. Particularly in methicillin resistant S. aureus infection treatment have been experienced great difficulties. Methicillin resistant S. aureus strains are resistant to beta lactam and most of the non beta lactam antibiotics. Therefore, glycopeptide antibiotics are the first option in the treatment of severe infections caused by methicillin resistant S. aureus. The study which aimed to investigate, presence of vancomycin resistance in methicillin resistant staphylococci, was conducted between January 2010 and November 2013. Total of 331 staphylococcal strains which were isolated from the variety of clinical samples (urine, sputum, blood, wound swabs, bronchial lavage fluid, catheter...etc.) which were sent to Clinical Microbiology laboratory of Duzce University Faculty of Medicine Research and Application Hospital were analyzed. Only methicillin resistant coagulase negative staphylococci and methicillin resistant S. aureus were included to the study. To detect methicillin resistance oxacillin screening agar, cefoxitin disk diffusion test and to detect vancomycin resistance vancomycin screening agar, standard E test, macro E test and PAP methods were used. 115 (54,2 %) of S. aureus isolates were found as methicillin resistant S. aureus. 66 (51,2%) of coagulase negative staphylococci isolates were found as methicillin resistant coagulase negative staphylococci. Only two of the 181 methicillin resistant staphylococci strains which inoculated to vancomycin screening agar were growed in first 24 hours. Both of them were S. aureus. These methicillin resistant S. aureus strains were found sensitive to vancomycin on standard and macro E test methods. There was not found any growth of vancomycin resistant strains with PAP method. As a result of these data, there was no growth of VIS and h/VIS strains in our hospital. It should be kept in mind that; in the treatment of suspected methicillin-resistant S. aureus infected patients, it should be kept in mind that usage of glycopeptides may lead to development of future hVISA and VISA, screening for vancomycin resistance should be performed in patients who do not respond to treatment. As a result, that it needs to be attentive in the usage of these exclusive antibiotics and as well as during pre-treatment and treatment close follow-up in microbiological aspect of patients was necessary and important had been considered. Key words: Staphylococcus aureus, coagulase negative staphylococci, methicillin, vancomycin, resistance, hVISA, VISA.