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

Area of Science:

• Microbiology
• Infectious Diseases
• Antimicrobial Resistance

Background:

• Heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) strains are increasingly reported globally.
• These strains are associated with vancomycin treatment failure, posing a significant clinical challenge.

Purpose of the Study:

• To screen clinical isolates of methicillin-resistant S. aureus (MRSA) for hVISA.
• To investigate the characteristics of hVISA strains, including cell wall thickness and biofilm formation.
• To assess the susceptibility of hVISA isolates to daptomycin.

Main Methods:

• Screening of 500 MRSA clinical isolates for hVISA using four different methods: Brain Heart Infusion agar with vancomycin, gradient plate, macro E-test, and GRD E test.
• Transmission electron microscopy (TEM) to evaluate cell wall thickness.
• Polystyrene microtiter plate assay to assess biofilm formation.
• Population analysis profile-area under the curve (PAP-AUC) for confirmation.

Main Results:

• The prevalence of hVISA varied by detection method and year, ranging from 9% to 13.9% in initial screening and 4.5% to 6.7% by PAP-AUC.
• Transmission electron microscopy revealed a significant increase in cell wall thickness in hVISA isolates (p<0.001).
• hVISA isolates demonstrated a distinct reduction in their ability to form biofilms.
• 24% of confirmed hVISA isolates were nonsusceptible to daptomycin.

Conclusions:

• hVISA strains exhibit increased cell wall thickness and impaired biofilm formation.
• A notable proportion of hVISA isolates are nonsusceptible to daptomycin, highlighting potential therapeutic challenges.
• Continued surveillance and characterization of hVISA are crucial for effective treatment strategies.