Increasing Trend of Heterogeneous Vancomycin Intermediate Staphylococcus aureus in a Tertiary Care Center of Northern India

Abstract

Heterogeneous vancomycin intermediate Staphylococcus aureus (hVISA) strains are increasingly reported, and their association with vancomycin treatment failure is a well-known problem worldwide. A total of 500 clinical isolates of methicillin-resistant S. aureus were screened for hVISA by four different methods from May 2011 to May 2014. The number of strains screened for hVISA from May to April in 2011–2012, 2012–2013, and 2013–2014 were 198, 123, and 179, respectively. hVISA strains were studied by transmission electron microscopy (TEM) for cell wall thickness and also for their ability to form biofilm on a polystyrene microtiter plate. hVISA strains detected by four different methods—brain heart infusion agar with vancomycin with 4 mg/L/gradient plate/macro E-test/and glycopeptide resistance detection (GRD) E test—were as follows: 11.6%/10%/9%, and 9.5% in 2011–2012, 12.1%/9.7%/8.9%, and 10.5% in 2012–2013, and 13.9%/11.7%/11.1%, and 12.8% in 2013–2014, respectively. Population analysis profile–area under curve analysis confirmed hVISA in 4.5% (9/198), 6.5% (8/123), and 6.7% (12/179) in respective years; 24% (7/29) of hVISA isolates were nonsusceptible to daptomycin. TEM showed a significant increase in cell wall thickness of hVISA isolates (p<0.001) with a distinct reduction in their biofilm formation ability.