Critical Care Medicine
Although Streptococcus pneumoniae and H. influenzae may be recovered during the first few days of a patients stay in the intensive care unit, they are rarely isolated thereafter. Staphylococcus aureus is the pathogen most frequently isolated from lower respiratory tract samples of patients with ventilator-associated pneumonia (VAP). Other commonly isolated pathogens include Pseudomonas aeruginosa, Enterobacter species, Klebsiella species, Acinetobacter baumannii, Proteus species, and Escherichia coli. Prevotella melaninogenica is among the most common anaerobic organisms isolated. Although anaerobic bacteria are frequently isolated from the oropharynx, and microaspiration has been demonstrated to be the predominant mechanism of VAP, the role of anaerobic bacteria in VAP is unclear, with many studies reporting a low incidence of anaerobic bacteria in VAP. Isolation of anaerobic bacteria requires adequate transport conditions and specific growth media. With these measures, anaerobic bacteria have been isolated in up to 25% of patients with VAP.
- Haemophilus influenzae.
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