Effect of antimicrobial therapy on bacterial burden in endotracheal aspirates from mechanically ventilated critical care patients with severe lower respiratory tract infection as assessed by the BIOFIRE® Filmarray® Pneumonia plus panel.

We investigated how antimicrobial therapy impacts bacterial loads in endotracheal aspirates from critical care patients with severe lower respiratory tract (LRT) infection as assessed by the Filmarray® pneumonia plus panel (FA-PP). This single-center, retrospective, observational study included 38 non-consecutive adult Intensive Care Unit patients undergoing invasive mechanical ventilation (IMV) with an FA-PP test returning detectable results for Pseudomonas aeruginosa, Enterobacterales, or Gram-positive microorganisms. Follow-up samples were collected within 12 days of the first one. P. aeruginosa was detected in nine patients. The P. aeruginosa load decreased in seven of these patients. All nine patients had been treated appropriately between sampling times. A total of 22 patients with Enterobacterales were included, representing 25 bacterial targets. Bacterial loads decreased for 15 targets in 12 patients, but either increased or remained unchanged for 10 targets in 10 patients. All but one patient were treated appropriately. A total of 19 patients had Gram-positive bacteria (n = 20) detected by the FA-PP, including S. pneumoniae (n = 10), S. aureus (n = 9), and S. pyogenes (n = 1). The administration of appropriate therapy (all patients) resulted in a decrease in bacterial burden for 14 targets in 14 patients. Bacterial loads remained unchanged or increased in for 6 targets in 6 patients. In conclusion the administration of appropriate antimicrobial therapy frequently results in a sizeable decrease in bacterial loads, as quantified by the FA-PP. This assay may prove useful for the assessment of the response to antibiotics in ICU patients with LRT infections undergoing invasive mechanical ventilation.