Critically ill patients receiving invasive mechanical ventilation have been found to have which of the following microorganisms not typically present in healthy individuals?

a. Anaerobes
b. Haemophilus species
c. Gram-negative bacilli
d. Viridans group of streptococci

ANS: C
During critical illnesses, particularly in patients with an endotracheal tube and those receiving mechanical ventilation, a dramatic shift occurs in the flora of the oropharyngeal tract to gram-negative bacilli and Staphylococcus aureus.