ANAEROBIC LUNG INFECTIONS
Where do anaerobes come from?
! Commonly overlooked as pathogens because special precautions are needed for
collection and transport, and culture growth is a slow process.
! Dominant bacteria of indigenous flora, whose role is to prevent colonization and
infection of pathogenic organisms from outside sources. Most prevalent on the
skin, nose, mouth, throat and colon. Bacteria thrive in microhabitats of reduced
oxygen tensions such as gingival crevices, tonsillar crypts, teeth plaque, hair
follicles, and sebaceous glands.
! Normally, in oral cavity there are about 10 CFU’s per ml and in the colon 10.
When do anaerobes cause infection?
! Normal aspiration: 45 % healthy subjects aspirate during sleep and normal
pulmonary clearance mechanism maintains the lower airways and parenchyma
sterile (glottic closure, cough reflex) with no clinical consequence.
! Infection requires a combination of aspiration of large inoculums of a virulent
bacteria AND impaired host defenses.
o Anaerobic overgrowth in the oral cavity due to periodontal disease.
Impaired host defense due to stupor/coma, seizure, alcoholism, general
anesthesia, dysphagia due to neurological or esophageal disease,
underlying pulmonary abnormalities (bronchiectasis, pulmonary infarct,
What are the top 3 anaerobes to cause infection?
! Fusobacterium nucleatum (gram-negative rods), peptostreptococcus (gram
positive cocci), micro-aerophillic streptococcus (gram positive cocci); less
commonly prevotella, bacteroides fragilis, clostridium perfringes, actinoymces
! In more than 2/3 cases part of a polymicrobrial infection with other anaerobes,
facultative and aerobic bacteria, most commonly in conjunction with
pneumococus, staph aureus, klebsiella and pseudomonas.
What is a typical clinical course of anaerobic pulmonary infection?
! Pneumonia: fever (no rigors), cough (no sputum) and infiltrate in aspiration
prone segments of lung (posterior segment of right u