Vancomycin susceptibility determination through various antimicrobial susceptibility tests in Methicillin-resistant Staphylococcus aureus (MRSA) strains isolated from a tertiary care hospital in Medellín.

ABSTRACT: Vancomycin has been the most effective antibiotic against infections caused by methicillin resistant Staphylococcus aureus (MRSA). To date there are no reports of Intermediate Vancomycin-Intermediate Staphylococcus aureus (VISA) or Vancomycin-Resistant Staphylococcus aureus (VRSA) in Colombia; however there is a high prevalence of MRSA and increased vancomycin use, which are contributing factors to their emergence. Additionally, routine methods used for detection of these strains such as automated and disc diffusion have limitations. OBJECTIVE To evaluate vancomycin susceptibility in a collection of MRSA strains isolated from patients between 2008-2010 in a University hospital of Medellin. MATERIALS AND METHODS 150 MRSA isolates were selected. The vancomycin minimum inhibitory concentration (MIC) was performed by Vitek-2 and Etest. Additionally, vancomycin screen agar plates were employed. RESULTS All of the isolates tested were susceptible to vancomycin, however, differences between the evaluated methods were observed: the 59.3% of the isolates (n = 89) showed an MIC ≤ 1 µg/mL by Etest, whereas by Vitek2, only the 22% (n = 33) of the isolates had this value. CONCLUSIONS We found a significant number of isolates with an MIC ≤ 1 µg/mL, which have been associated with increased risk of treatment failure. These results show the relevance of permanent surveillance of antibiotic resistance, to achieve the establishment of appropriate control strategies. comycin has been the most effective antibiotic against infections caused by methicillin resistant Staphylococcus aureus (MRSA). To date there are no reports of Intermediate Vancomycin-Intermediate Staphylococcus aureus (VISA) or Vancomycin-Resistant Staphylococcus aureus (VRSA) in Colombia; however there is a high prevalence of MRSA and increased vancomycin use, which are contributing factors to their emergence. Additionally, routine methods used for detection of these strains such as automated and disc diffusion have limitations. Key words: Antimicrobial Susceptibility Testing. Methicillin-resistant Staphylococcus aureus (MRSA). Resistance. Vancomycin.RESUMEN: La vancomicina ha sido el antibiótico más eficaz contra las infecciones causadas por Staphylococcus aureus resistente a la meticilina (SARM). En Colombia, hasta la fecha, no se han reportado aislamientos con sensibilidad intermedia o resistentes a vancomicina, no obstante se presenta una prevalencia alta de SAMR y un alto consumo de vancomicina, condiciones que favorecerían su aparición. Adicionalmente, los métodos automatizados y de difusión en disco, empleados de rutina para la detección de estas cepas presentan limitaciones. OBJETIVO Determinar la susceptibilidad a vancomicina en una colección de aislamientos de SARM obtenidos de pacientes durante los años 2008-2010 en un hospital universitario de la ciudad de Medellín. MATERIALES Y MÉTODOS Se seleccionaron 150 aislamientos de SARM en los cuales la susceptibilidad a vancomicina se determinó empleando agar de tamización BHI-vancomicina y la concentración Inhibitoria mínima (CIM) se determinó por Vitek-2 y Etest. RESULTADOS La totalidad de los aislamientos evaluados fueron sensibles a vancomicina. Se observaron diferencias entre los métodos evaluados, 59,3% de los aislamientos (n=89), presentaron una CIM ≤ 1 µg/mL, por Etest, mientras que por Vitek2 solo el 22% (n=33) presentaron este valor. CONCLUSIÓN Se determinó un numero importante de aislamientos con una CIM ≤ 1 µg/mL, las cuales se han asociado con mayor riesgo de falla terapéutica. Estos resultados evidencian la importancia de establecer una vigilancia constante de la resistencia a antibióticos, para lograr el establecimiento de estrategias adecuadas de control. Palabras clave: Pruebas de susceptibilidad antimicrobiana. Staphylococcus aureus meticilino resistente (SARM). Resistencia. Vancomicina