Study objective: To compare quantitative growth from a calibrated loop to growth from the standard serial dilution technique of culturing bronchoscopic protected specimen brush (PSB) samples and to determine the effect of refrigeration of the PSB sample on subsequent quantitative growth.
Design: Laboratory stock cultures were sampled with a PSB and cultured by both standard 100-fold serial dilution as well as 1:100 mL and 1:1,000 mL calibrated loops. Stock cultures were also sampled with a PSB and growth before and after refrigeration for 24 h at 4 degrees C (both serial dilution and calibrated loops) was compared. Clinical PSB samples from seven patients suspected of having lower respiratory tract infections were cultured by both techniques as well.
Setting: Clinical research laboratory and teaching hospital.
Patients and interventions: PSB samples from inpatients and outpatients who had clinically indicated bronchoscopy. No interventions.
Measurements and results: Quantitative growth from the 1:1,000 mL calibrated loop was within 1 log10 of growth from the serial dilution technique for 20 of 21 organisms, including 2 yeasts. Except for Haemophilus influenzae (known to be cold intolerant), there were no important differences in growth of bacteria before and after 24 h at 4 degrees C. For quantitative bacterial growth, there was a significant correlation between serial dilution and the 1:1,000 mL loop cultures (r=0.86, p < 0.0001).
Conclusion: In this study, quantitative growth from a single 1:1,000 mL loop culture of PSB samples was comparable to growth from the standard serial dilution technique. Our results also suggest that overnight refrigeration of PSB samples may be possible in certain clinical situations.