Study of Decreased Susceptibility to Vancomycin in Methicillin-Resistant Staphylococcus aureus Strains isolated from a Romanian Multidisciplinary Emergency Hospital

The clinical relevance of Staphylococcus aureus strains with heterointermediate susceptibility to vancomycin (hVISA) is still controversial, however they could be responsible for treatment failures in patients treated with vancomycin. The lack of standardization and the complexity of testing methods are the main challenge in indentifying such strains. The aim of our study was to evaluate the frequency of hVISA strains in Targu-Mures Clinical Emergency Hospital. One hundred twenty-two, non-duplicate, methicillin-resistant S. aureus (MRSA) isolates susceptible to vancomycin using standard E-test (MIC≤2 mg/L) were screened for heteroresistance with Glycopeptide Resistance Detection test (E-test GRD). Population analysis profile-area under the curve (PAP/AUC) method was used for confirmation. Twenty-four strains (19.5%) were found positive with the screening method. Two of them (1.63%) were confirmed having hVISA phenotype and no strains with intermediate vancomycin susceptibility (VISA) were detected. In conclusion, the rate of MRSA strains with reduced vancomycin susceptibility was low. However, their monitoring may be useful, taking into consideration the wide usage of glycopeptides in the treatment of serious MRSA infections. Relevanța clinică a tulpinilor Staphylococcus aureus cu susceptibilitate heterointermediară la vancomicină (hVISA) nu este complet elucidată, totuși acestea pot fi responsabile pentru eșec terapeutic la pacienții tratați cu vancomicină. Lipsa standardizării și complexitatea metodelor de detectare sunt provocări importante in identificarea acestor tulpini. Scopul studiului a fost evaluarea frecvenței tulpinilor hVISA în Spitalul Clinic Județean de Urgență Târgu-Mureș. O sută douăzeci și două de tulpini de S. aureus meticilino-rezistente (MRSA), susceptibile la vancomicina cu E-test standard (CMI≤2 mg/L), au fost testate pentru heterorezistență cu metoda E-test GRD (Glycopeptide Resistance Detection). Pentru confirmare s-a folosit analiza populațională. Douăzeci și patru de tulpini (19.5%) au fost selectate cu metoda screening. Două dintre acestea (1.63%) au fost confirmate fiind hVISA, nici un izolat nu avea susceptibilitate intermediară la vancomicină (VISA). Rata tulpinilor hVISA a fost scazută. Monitorizarea lor poate fi totuși importanta, luând in considerare ca glicopeptidele sunt larg utilizate pentru tratamentul infecțiilor severe cauzate de MRSA.