An abscess may be described as nonspecific if the probable pathogen is not recognized in the expectorated sputum or as a fetid abscess if the cause is thought to be anaerobic bacteria. The classification depends on the microorganism causing the abscess. In most cases, it is polymicrobial, which includes anaerobic bacteria such as Bacteroides , Prevotella , Peptostreptococcus , Fusobacterium , or streptococci. Monomicrobial lung abscess is caused by Streptococcus, Staphylococcus aureus, Klebsiella pneumoniae, Streptococcus pyogenes, Burkholderia pseudomallei, Hemophilus influenzaetipe b, Nocardia, and Actinomyces.
