 klebsiella pneumoniae is a gram-negative, nonmotile, encapsulated, lactose-fermenting, facultative anaerobic, rod-shaped bacterium. although found in the normal flora of the mouth, skin, and intestines, it can cause destructive changes to human lungs if aspirated, specifically to the alveoli resulting in bloody sputum. in the clinical setting, it is the most significant member of the klebsiella genus of enterobacteriaceae. k oxytoca and k rhinoscleromatis have also been demonstrated in human clinical specimens. in recent years, klebsiellae have become important pathogens in nosocomial infections. it naturally occurs in the soil, and about 30% of strains can fix nitrogen in anaerobic conditions. as a free-living diazotroph, its nitrogen fixation system has been much-studied, and is of agricultural interest, as k. pneumoniae has been demonstrated to increase crop yields in agricultural conditions. members of the klebsiella genus typically express two types of antigens on their cell surfaces. the first, o antigen, is a component of the lipopolysaccharide (lps), of which 9 varieties exist. the second is k antigen, a capsular polysaccharide with more than 80 varieties. both contribute to pathogenicity and form the basis for serogrouping. it is closely related to k. oxytoca from which it is distinguished by b
Enterobacteria Gram-negative_bacteria Pathogenic_bacteria Polysaccharide_encapsulated_bacteria