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Characterization of Vancomycin Resistance and Associated Genes in Clinical Isolates of Enterococcus Species

Madhumala Shanmugasundaram1, MuthuLakshmi BackiaSubramanian1, Shanthi Mariappan1

  • 1Microbiology, Sri Ramachandra Institute of Higher Education and Research, Chennai, IND.

Cureus
|July 31, 2026
PubMed

Insights

Vancomycin resistance in Enterococcus is increasing, with the vanA gene being the most common cause in clinical isolates. This study highlights the need for further research into vancomycin-resistant Enterococci (VRE) mechanisms.

Area of Science:

  • Clinical Microbiology
  • Infectious Diseases
  • Molecular Epidemiology

Background:

  • Vancomycin is a critical antibiotic for treating multidrug-resistant Enterococcal infections.
  • Rising vancomycin minimum inhibitory concentration (MIC) values and resistance are significant clinical concerns.
  • Characterizing vancomycin resistance mechanisms is essential for effective treatment strategies.

Purpose of the Study:

  • To detect and characterize vancomycin resistance in clinical Enterococcus isolates.
  • To correlate phenotypic vancomycin resistance with the presence of specific vancomycin resistance genes (vanA, vanB, vanC1, vanC2/3, vanD, vanE, vanG).
  • To analyze the prevalence of different vancomycin resistance genotypes in Enterococcus species.

Main Methods:

  • Phenotypic susceptibility testing using Kirby-Bauer disc diffusion and agar dilution methods for MIC determination.
  • Molecular analysis employing Polymerase Chain Reaction (PCR) to detect vancomycin resistance genes.
  • Analysis of 266 consecutive, non-repetitive clinical Enterococcus isolates collected from 2023-2024.

Main Results:

  • Vancomycin resistance was detected in 74 out of 266 (27.8%) Enterococcus isolates, with MICs ≥ 32 μg/mL.
  • The vanA gene was the most prevalent genotype, found in 70 resistant isolates, primarily in Enterococcus faecium.
  • Enterococcus gallinarum isolates showed vanC1 and, in one case, a co-occurrence of vanA and vanC1 genes; no vanB, vanC2/3, vanD, vanE, or vanG genes were detected.

Conclusions:

  • The vanA genotype is the predominant mechanism for vancomycin resistance in the studied clinical Enterococcus isolates.
  • The increasing prevalence of vancomycin-resistant Enterococci (VRE) necessitates ongoing surveillance and research.
  • Emergence of linezolid-resistant Enterococci underscores the urgent need for deeper understanding of VRE resistance mechanisms.
Keywords:
healthcareminimum inhibitory concentrationpolymerase chain reactionvana genevanc1vancomycin-resistant enterococci

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