The genus Klebsiella, which is named after the microbiologist Edwin Klebs, belongs to the family Enterobacteriaceae. The most important representatives are Klebsiella pneumoniae and Klebsiella oxytoca. Other species with importance in human medicine are Klebsiella pneumoniae subspecies ozaenae and subspecies rhinoscleromatis. Klebsiella are immobile, have a polysaccharide capsule and are easy to cultivate on simple nutrient media. The colonies are large and slimy. Most strains can utilize glucose and citrate as the sole carbon source. Klebsiella oxytoca produces only one of the four Klebsiella spp indole. Such as Escherichia coli have Klebsiella O and K antigens.
The polysaccharide capsule that carries the K-antigen acts antifagotsitare.