MICROBIOLOGY OF HOSPITAL-ACQUIRED PNEUMONIA

The microbiology of hospital-acquired pneumonia reflects the pathogene sis and risk factors associated with both the disease itself and the v arious pathogens. The etiologic agents include aerobic gram-negative b acilli such as the Enterobacteriaceae, Haemophilus influenzae, Pseudom onas aeruginosa, and Acinetobacter spp,, as well as grampositive cocci such as Staphylococcus aureus and Streptococcus pneumoniae. Other bac terial pathogens that may occur depending on the risk factors include anaerobes and Legionella spp. This article reviews these pathogens fro m the point of view of their relevant microbiologic features and the r isk factors that predispose patients to infection with these organisms . A discussion of the relevant antimicrobial resistance issues is also included. The latter provides an overview of resistance development a nd means of spread among pathogens as well as a more detailed examinat ion of the specific resistance mechanisms to antibiotics as they relat e to the pathogens that cause hospital-acquired pneumonia.