Screening for Vancomycin-Resistant and Intermediate S. aureus (VRSA & VISA) by the E-test in the hospitals of Bethlehem and Jerusalem Districts

Abstract

The glycopeptide antibiotic vancomycin is frequently used as the drug of choice for the treatment of infections caused by methicillin-resistant Staphylococcus aureus (MRSA). MRSA has been reported to cause severe life threatening infections that mandate the utilization of aggressive antimicrobial therapy such as the glycopeptides to clear these infections. However, the increase utilization of glycopeptides and in particular vancomycin has led to the emergence of vancomycin-intermediate S. aureus (VISA) and vancomycin-resistant S. aureus (VRSA). The present study was carried out to screen for the presence of VISA and VRSA in the hospitals of Bethlehem and East Jerusalem districts. A total of 190 S. aureus isolates from blood culture and abscesses were subjected to MIC testing using the E-test for vancomycin with concentration 0.016-256 µg/ml. All of the 190 S. aureus isolates were found to be sensitive to vancomycin according to the Clinical and Laboratory Standard Institute (CLSI) M40-A antimicrobial guidelines where vancomycin MIC ≤ 2µg/ml is considered as susceptible, MIC = 4-8 µg/ml is intermediate and MIC ≥ 16 µg/ml is resistant. Of the 190 S. aureus, 4.2% (8/190) were sensitive to vancomycin at a concentration ≤ 2 µg/ml, 40.5% (77/190) with a concentration ≤ 1.5 µg/ml, 46.8% (89/190) with a concentration ≤ 1 µg/ml, and 8.4% (16/190) with a concentration ≤ 0.5 µg/ml. The present study reveals that vancomycin still remains the drug of choice as no isolates in both districts were found to be either VISA or VRSA; However, the physicians must be aware that the misuse of prescribing vancomycin might lead to the emergence of VISA strains as 4.2% (8/190) of the tested isolates had the highest vancomycin MIC of ≤ 2 µg/ml.