The most likely cause of aspiration pneumonia is:
A. A mixture of aerobes and anaerobesNormal oropharyngeal secretions contain many more Streptococcus species and more anaerobes (approximately 1 x 108 organisms/mL) than aerobes (approximately 1 x 107 organisms/mL). Pneumonia that follows from aspiration, with or without abscess development, is typically polymicrobial. An average of two to four isolates present in large numbers have been cultured from lung abscesses sampled percutaneously. Overall, at least 50% of these infections are caused by purely anaerobic bacteria, 25% are caused by mixed aerobes and anaerobes, and 25% or fewer are caused by aerobes only. In nosocomial pneumonia, 60 to 70% of the organisms are gram-negative bacteria, including Klebsiella pneumoniae, Haemophilus influenzae, Proteus species, Pseudomonas aeruginosa, Escherichia coli, Enterobacter cloacae, and Eikenella corrodens. Immunosuppressed patients may develop abscesses because of the usual pathogens as well as less virulent and opportunistic organisms such as Salmonella species, Legionella species, Pneumocystis carinii, atypical mycobacteria, and fungi.