Abstract
Interpretation of the protected specimen brush (PSB) technique is based on quantitative bacterial cultures (QC), which unfortunately requires at least 24 h. We prospectively compared the diagnostic value of direct examination (DE) and QC of PSB specimens in 75 patients with suspected pneumonia. We also determined the optimal technique for DE. QC was performed using the serial dilution technique. From the original suspension, two cytospin slides were obtained and stained by the May-Grunwald Giemsa (MGG) and the Gram method for DE. If the prescreening on the MGG-stained slide was positive, the morphology and the Gram staining of the organisms were assessed on the Gram-stained slide. Using the 10(3) colony forming units (cfu.ml-1) threshold for defining PSB as positive or negative, DE had a sensitivity of 85% and a specificity of 94%. In a parallel in vitro study, 18 pairs of PSB specimens were collected from respiratory secretions inoculated with S. aureus. From each pair, one brush was processed as described above and the other was smeared on a glass slide prior to performance of QC. Using direct smear instead of cytocentrifuged preparation, slightly but significantly affected QC. Direct examination of cytospin slides is highly predictive of quantitative bacterial culture results, and provides rapid information regarding the Gram-stain morphology of the causative organisms. It may therefore guide initial therapy.
