Introduction: Staphylococcus aureus (S. aureus) is a common cause of ventilator-associated pneumonia. Rapid and accurate detection of lower respiratory tract colonization and/or infection with S. aureus may inform targeted preventive and therapeutic strategies. To investigate this, we compared semi-quantitative (SQ)-culture results from 79 endotracheal aspirates (ETA) collected from mechanically-ventilated patients, to two culture and two non-culture-based methods for detection of S. aureus.
Methods: ETA analyzed by routine SQ-culture on blood and colistin-nalidixic-acid agar was compared to: (i) quantitative (Q-) culture on chromogenic COLOREX™ Staph aureus; (ii) enrichment in brain-heart-infusion broth followed by plating on blood agar and COLOREX™; (iii) nuc-based TaqMan qPCR, and (iv) GeneXpert MRSA/SA ETA assay.
Results: Of the 79 ETA samples analyzed by SQ-culture, 39 samples were positive, and 40 negative for S. aureus. Two samples negative for S. aureus by SQ-culture were, however, S. aureus-positive by the other four methods and were considered positive. Appending these two samples as positive in the SQ-culture results, sensitivities-specificities for Q-culture, enrichment-culture, TaqMan qPCR and GeneXpert were 100-95, 100-92, 100-53% and 100% - 100, respectively. The lower specificities of Q-culture, enrichment-culture, and TaqMan qPCR was because of their higher sensitivities, although TaqMan qPCR also detected S. aureus-specific extracellular DNA.
Conclusion: This first evaluation of the GeneXpert MRSA/SA ETA assay with ETA samples found it to be highly sensitive, specific, user-friendly (hands-on time ~ 5 min.), and rapid (~ 66 min. assay time). Where this equipment is not available, we recommend implementing more sensitive culture-based methods for improved S. aureus detection in ETA samples.
- Bacterial Proteins/genetics
- Diagnostic Tests, Routine/methods
- Methicillin-Resistant Staphylococcus aureus/classification
- Micrococcal Nuclease/genetics
- Pneumonia, Ventilator-Associated
- Real-Time Polymerase Chain Reaction
- Sensitivity and Specificity
- Staphylococcal Infections/diagnosis
- Staphylococcus aureus/classification
- Ventilators, Mechanical/microbiology