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Updated: Jun 2, 2026
Biosensor for Detection of Antibiotic Resistant Staphylococcus Bacteria
Published on: May 8, 2013
Detection of intermediately vancomycin-susceptible and heterogeneous Staphylococcus aureus isolates: comparison of
K Riederer1, S Shemes, P Chase
1Department of Medicine, St. John Hospital and Medical Center, Detroit, Michigan, USA.
Abstract:
Detection of Staphylococcus aureus isolates with intermediate vancomycin susceptibility (VISA) and heteroresistance (hVISA) remains problematic. The population analysis profile/area under the curve (PAP/AUC) is the gold standard but is cumbersome. We compared the performance of two Etest screening methods (macromethod [MAC] and glycopeptide resistance detection [GRD]) plus brain heart infusion (BHI) agars supplemented with 3 (BHI-V3) or 4 (BHI-V4) mg/liter vancomycin in detecting hVISA and/or VISA phenotypes. Etest hVISA screenings were done in parallel for 485 saved methicillin-resistant S. aureus (MRSA) blood isolates according to the manufacturer's instructions. The PAP/AUC was measured for all isolates according to the modified method. PAP/AUC test isolate/Mu3 ratios of <0.9, 0.9 to 1.3, and >1.3 were considered positive for susceptible MRSA (S-MRSA), hVISA, and VISA, respectively. PAP/AUC revealed seven VISA and 33 hVISA phenotypes. MAC screening was positive for 30 (75.0%) hVISA/VISA and 49 (11.0%) S-MRSA isolates. GRD screening was positive for 28 (70.0%) hVISA/VISA and 63 (14.2%) S-MRSA isolates. Growth on BHI-V3 was noted in all hVISA/VISA and 24 (5.4%) S-MRSA isolates. Growth on BHI-V4 was noted in all VISA and four (12.1%) hVISA isolates. None of the S-MRSA isolates grew on BHI-V4 agar. The sensitivity, specificity, and positive (PPV) and negative (NPV) predictive values were 75.0%, 89.0%, 38.0%, and 97.5% for MAC; 70.0%, 85.8%, 30.8%, and 97.0% for GRD; 100%, 94.6%, 62.5%, and 100% for BHI-V3; and 100, 99.2%, 63.6%, and 100% for BHI-V4 (for detecting VISA). These findings suggest that both Etest screening methods have excellent NPV, but positive results require confirmation. BHI-V3 and BHI-V4 agars provide more precise identification of hVISA and VISA, respectively; they may be reasonable alternatives to PAP/AUC.
Insights
Detecting vancomycin-resistant Staphylococcus aureus (VISA) and heteroresistant (hVISA) strains is challenging. Brain heart infusion (BHI) agars with vancomycin offer precise identification of VISA and hVISA phenotypes, potentially replacing cumbersome gold-standard methods.
Area of Science:
- Clinical microbiology
- Infectious diseases
- Antimicrobial resistance
Background:
- Detection of vancomycin intermediate Staphylococcus aureus (VISA) and heteroresistant (hVISA) phenotypes is critical for effective treatment of methicillin-resistant S. aureus (MRSA) infections.
- The gold standard population analysis profile/area under the curve (PAP/AUC) method is time-consuming and complex.
Purpose of the Study:
- To evaluate the performance of two Etest screening methods (macromethod [MAC] and glycopeptide resistance detection [GRD]) and two brain heart infusion (BHI) agar-based methods (BHI-V3 and BHI-V4) for detecting hVISA and VISA phenotypes.
- To compare these methods against the established PAP/AUC gold standard.
Main Methods:
- 485 saved MRSA blood isolates were tested using Etest MAC and GRD screening methods.
- Isolates were also cultured on BHI agar supplemented with 3 mg/liter (BHI-V3) or 4 mg/liter (BHI-V4) vancomycin.
- PAP/AUC was performed on all isolates to determine susceptibility, hVISA, and VISA phenotypes.
Main Results:
- PAP/AUC identified 7 VISA and 33 hVISA phenotypes among the 485 MRSA isolates.
- BHI-V3 agar detected all hVISA/VISA isolates with 100% sensitivity and 94.6% specificity.
- BHI-V4 agar detected all VISA isolates with 100% sensitivity and 99.2% specificity, showing excellent performance for VISA detection.
Conclusions:
- Brain heart infusion agars supplemented with vancomycin (BHI-V3 and BHI-V4) demonstrate high sensitivity and specificity for identifying hVISA and VISA phenotypes, respectively.
- These BHI agar methods may serve as practical and accurate alternatives to the cumbersome PAP/AUC method for routine clinical laboratory use.
- While Etest screening methods offer good negative predictive values, positive results warrant further confirmation.
