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Published on: September 8, 2021
A 1 year surveillance study of glycopeptide-intermediate Staphylococcus aureus strains in a French hospital
Fabien Garnier1, Delphine Chainier, Timothy Walsh
1Laboratoire de Bactériologie-Virologie-Hygiène, CHU Dupuytren, EA 3175, Limoges, France. fabien.garnier@unilim.fr
Objectives:
Glycopeptides are the drugs of choice to treat infections due to methicillin-resistant Staphylococcus aureus, but since 1995, glycopeptide-intermediate S. aureus (GISA) and heterogeneous GISA (hGISA) have been reported worldwide. Detection of reduced susceptibility to glycopeptides in S. aureus is very difficult in a routine clinical laboratory. The aim of this study was to investigate the prevalence of hGISA/GISA strains using a three-step approach during a 1 year period.
Methods:
The following algorithm was adopted: (i) brain heart infusion agar with 4 mg/L teicoplanin was used to screen S. aureus strains for reduced susceptibility to glycopeptides; (ii) for each agar screen-positive strain, an Etest macromethod using modified cut-off values (vancomycin and teicoplanin > or =4 mg/L) was used to detect potential hGISA/GISA; and (iii) the population analysis profile (PAP) method was finally used to confirm the hGISA/GISA phenotype.
Results:
In total, 2300 strains of S. aureus were screened and 255 (11%) were categorized as hGISA with the PAP method, whereas no GISA strains were detected. Standard MIC values and current MIC breakpoints could not discriminate the hGISA/GISA phenotype from glycopeptide-susceptible S. aureus. Thus laboratories using currently standardized MIC methods cannot be expected to detect S. aureus strains that may exhibit reduced susceptibility to glycopeptides. Molecular typing by PFGE revealed that 238 strains belonged to the same clone.
Conclusions:
A clonal hGISA strain has disseminated within our hospital. The method described in this study has to be further investigated to see if it is applicable to other S. aureus strains.
Insights
A new three-step method detected 11% of heterogeneous vancomycin-intermediate Staphylococcus aureus (hGISA) strains, which are difficult to identify using standard laboratory methods. This finding highlights a concerning prevalence of hGISA in clinical settings.
Area of Science:
- Clinical microbiology
- Infectious diseases
- Antimicrobial resistance
Background:
- Glycopeptides are crucial for treating methicillin-resistant Staphylococcus aureus (MRSA) infections.
- The emergence of glycopeptide-intermediate S. aureus (GISA) and heterogeneous GISA (hGISA) poses a significant challenge.
- Detecting reduced glycopeptide susceptibility in S. aureus is difficult in routine clinical laboratories.
Purpose of the Study:
- To investigate the prevalence of hGISA/GISA strains.
- To evaluate a three-step diagnostic approach for identifying these strains over a one-year period.
Main Methods:
- Screening S. aureus strains using brain heart infusion agar with 4 mg/L teicoplanin.
- Employing an Etest macromethod with modified cut-off values (vancomycin and teicoplanin ≥ 4 mg/L) for initial detection.
- Confirming the hGISA/GISA phenotype using the population analysis profile (PAP) method.
Main Results:
- Out of 2300 S. aureus strains, 255 (11%) were identified as hGISA by PAP; no GISA strains were found.
- Standard MIC values and current breakpoints failed to differentiate hGISA/GISA from susceptible strains.
- Molecular typing revealed a predominant clone among the identified hGISA strains.
Conclusions:
- A clonal hGISA strain has disseminated within the hospital.
- The developed three-step method shows promise for detecting hGISA/GISA.
- Further investigation is needed to assess the broader applicability of this method to other S. aureus strains.
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