Emergence of Vancomycin Intermediate Staphylococcus aureus (VISA) in a Tertiary Care Hospital in Lahore: An Alarming Situation

Abstract

Objectives: To assess the current situation of vancomycin MIC values and to find out the possible presence of
vancomycin intermediate or resistant Staphylococcus aureus strains in a tertiary care hospital of Lahore, Pakistan.
Study Design: Non-interventional, descriptive study.
Place and Duration of Study: Pathology Department, Post Graduate Medical Institute, Lahore from February 2013
to October 2013.
Methodology: A total of 50 consecutive isolates of methicillin resistant Staphylococcus aureus (MRSA) were
identified by using cefoxitin disc diffusion test. The confirmation of methicillin resistance was done by PBP2a
latex agglutination test. E-test strips (AB Biodisk, Biomeurix) were used for the determination of Vancomycin
MIC values for MRSA strains and results were interpreted according to clinical and laboratory standards institute
(CLSI) guidelines.
Results: Result of our study showed that the range of MIC values of vancomycin for MRSA was 1.5-4 ug/ml.
Among a total of 50 MRSA isolates, four strains (8%) were identified as vancomycin intermediate Staphylococcus
aureus (VISA) with MIC value of 4μg/ml. Mean vancomycin MIC value was 2.5ug/ml whereas MIC50 and
MIC90 values of vancomycin were 2ug/ml and 3ug/ml respectively.
Conclusion: The emergence of vancomycin Intermediate Staphylococcus aureus in our setup is an alarming
situation. The widespread use of vancomycin for the treatment of MRSA might have induced a selection pressure,
thus resulted in the emergence of these notorious resistance strains. Our study accentuates the need for
continuous monitoring of vancomycin MIC levels in MRSA infections. A strict regulation on irrational antibiotic
usages might be an effective approach in this direction. Proper infection control policies must be adopted to
prevent the transmission of resistance strains.