Molecular and Clinical Features of Heterogeneous Vancomycin-Intermediate Staphylococcus aureus in Tertiary Care Hospitals in South India

Abstract

Objectives: This study aimed to detect heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) among methicillin resistant S. aureus (MRSA) isolated from healthcare-associated infections and identify staphylococcal cassette chromosome mec (SCCmec) types. Methods: Isolation and identification of MRSA were done using standard bacteriological methods. Antimicrobial susceptibility testing was done using Kirby-Bauer disc diffusion and macrolide-lincosamide-streptogramin B (MLSB) phenotypes identified using D test. The minimum inhibitory concentration (MIC) of vancomycin was determined using agar dilution. hVISA were confirmed by modified population analysis profile-area under the curve (PAP-AUC) test. SCCmec types and Panton-Valentine leukocidin (pvl) were detected using multiplex PCR. Results: Out of 220 MRSA stains, 14 (6.4%) were hVISA. None of the MRSA isolate was vancomycin intermediate or resistant. All hVISA were susceptible to linezolid and teicoplanin. Macrolide-streptogramin B (MSB) phenotype was present in 42.9% hVISA. 92.9% hVISA strains had vancomycin MIC in the range 1-2 µg/mL. Majority of hVISA and vancomycin susceptible MRSA were isolated from skin and soft tissue infections. SCCmec III and IV were present in 50% and 35.7% hVISA respectively. 14.3% hVISA harboured SCCmec V. Conclusion: The rate of hVISA among MRSA was 6.4%. MRSA strains should be tested for hVISA before starting vancomycin treatment. None of the isolates was vancomycin intermediate or resistant. All the hVISA strains were susceptible to linezolid and teicoplanin. The majority of hVISA were isolated from skin and soft tissue infections. The majority hVISA harboured SCCmec III and IV.
 Keywords: MRSA; Hospital infection; Molecular typing; Vancomycin