Investigation of Reduced Vancomycin Susceptibility in Methicillin-Resistant Staphylococcus aureus Strains

Metisiline Dirençli Staphylococcus aureus Suşlarında Vankomisine Karşı Azalmış Duyarlılığın Araştırılması

Abstract

Objective: Staphylococcus aureus is one of the most important factors that leads to community-acquıired and nosocomial infections in the whole world. Vancomycinresistant S. aureus (VRSA) bacteria can be detected in routine sensitivity tests because they have very high minimal inhibitory concentration values aganist vancomycin. Vancomycin-intermediate S. aureus (VISA)/ heterogenous VISA (hVISA) bacterial strains can not be detected using routine sensitivity tests applied in laboratories. In our study we aimed to search the frecuency of VISA and hVISA strains isolated from various samples sent to our hospital microbiology laboratory between January 2008-August 2013. Fifty-two MRSA bacteriel strains.samples isolated and stocked in microbiology laboratory of our hospital at -80°C were used to investigate the freguency of VISA and hVISA isolates.Materials and Methods: These samples were first subjected to molecular tests by multipleks polymerase chain reaction (PCR) method for detecting mecA, nuc and 16S genes. Vancomycin microdilution, gradient test, vancomycin screen agar (BHIA-V6) were applied on these samples. Macrogradient test and PAP-AUC method were runned on nine bacterial strains which were reproduced in screen agar.Results: mecA gene zone was displayed in 52 bacterial strains by PCR. All bacterial strains are found to be sensitive to vancomycin (MIK≤2 µg/ml) by using gradient test and broth microdilution method. Bacterial growth was observed within the first 24 (n=8), and 48 hours (n=1) in indicated number of samples in brain heart infusion (BHIV6) agar screen test which contained 6 µg/ml vancomycin. In macrogradient test MIK values were found to be ≥8 µg/ml in 5 strains, and ≤8 µg/ml in four bacterial strains Nine bacterial strains (17.3%) were evaluated to be hVISA according to the population analysis profile results.Conclusion: According to these results we found that MRSA strains which have decreased sensitivity aganist vancomycin also present in our hospital. These bacterial strains can not be detected with routine laboratory tests. These bacterial strains should be identified to prevent unsuccesful treatment because nowadays glycopeptide antibiotics are the first choice in the treatment of MRSA

Özet

Amaç: Staphylococcus aureus, tüm dünyada toplum ve hastane kaynaklı enfeksiyonlara yol açan en önemli etkenlerden biridir. Metisiline dirençli Staphylococcus aureus (MRSA)'da bakteriler vankomisine karşı çok yüksek minimal inhibitör konsantrasyon değerlerine sahip olduğundan, rutin duyarlılık testlerinde tespit edilebilmektedir. "Vankomisin-intermediate" S. aureus (VISA)/heterojen VISA (hVISA) suşlarının ise laboratuvarlarda uygulanan rutin duyarlılık testleriyle saptanması güçtür. Çalışmamızda, Ocak 2008-Ağustos 2013 tarihleri arasında hastanemiz mikrobiyoloji laboratuvarına gönderilmiş çeşitli örneklerden izole edilip -80°C'de stoklanmış 52 adet MRSA suşu kullanılarak VISA ve hVISA izolatlarının sıklığının araştırılması amaçlanmıştır. Gereç ve Yöntem: Bu örnekler öncelikle multipleks polimerize zincir reaksiyonu (PZR) yöntemi ile mecA, nuc ve 16S genleri açısından moleküler olarak test edildi. Bu suşlara vankomisin mikrodilüsyon, gradient test, vankomisin agar tarama (BHI-V6) uygulandı. Agar taramada üreyen dokuz suşa makrogradient test ve PAP-AUC yöntemi uygulandı.Bulgular: Elli iki suşta PZR ile mecA gen bölgesi gösterildi. Gradient-test ve buyyon mikrodilüsyon yöntemi ile tüm suşların vankomisine duyarlı (MİK değeri =8 ?g/ml olarak, dört suşun MİK değeri