Rapid simultaneous identification and quantitation of Staphylococcus aureus and Pseudomonas aeruginosa directly from bronchoalveolar lavage specimens using automated microscopy

Diagnosis of ventilator-assisted pneumonia (VAP) requires pathogen quantitation of respiratory samples. Current quantitative culture methods require overnight growth, and pathogen identification requires an additional step. Automated microscopy can perform rapid simultaneous identification and quantitation of live, surface-immobilized bacteria extracted directly from patient specimens using image data collected over 3 h. Automated microscopy was compared to 1 μL loop culture and standard identification methods for Staphylococcus aureus and Pseudomonas spp. in 53 remnant bronchoalveolar lavage specimens. Microscopy identified 9/9 S. aureus and 7/7 P. aeruginosa in all specimens with content above the VAP diagnostic threshold. Concordance for specimens containing targets above the diagnostic threshold was 13/16, with concordance for sub-diagnostic content of 86/90. Results demonstrated that automated microscopy had higher precision than 1 μL loop culture (range ~0.55 log versus ≥1 log), with a dynamic range of ~4 logs (~103 to 106 CFU/mL).