Effects of antibiotics on protected specimen brush sampling in ventilator-associated pneumonia

The effects of antibiotic treatment on the results of protected specimen brushing (PSB) in ventilator-associated pneumonia were prospectively assessed by performing this procedure before antibiotic treatment, and 12, 24, 48 and 72 h after initiation of antibiotic treatment, in 35 ventilated patients who developed pneumonia during mechanical ventilation. The number of micro-organisms isolated, their concentration (colony-forming units (cfu)·mL−1), and the number of cases with a positive PSB (≥103 cfu·mL−1) were evaluated. Within 12 h of the initiation of effective antibiotic treatment a rapid, significant decrease in the numbers of organisms isolated, their individual concentrations and the percentage of positive PSB results were observed. Certain bacterial species ( Streptococcus pneumoniae , Haemophilus influenzee ) appeared to be more vulnerable to antibiotics than others ( Staphylococcus aureus , Pseudomonas aeruginosa , Acinetobacter baumanni ). This data confirms that prior antibiotic treatment, even after only a few hours of activity, significantly decreases the sensitivity of protected brush specimen; this effect appears to be particularly marked among the species involved in early ventilator associated pneumonia. This study was supported by a grant awarded by the “Fondo de Investigaciones Sanitarias de la Seguridad Social” (FIS) No 94/0874.