克雷伯氏肺炎菌（Klebsiella pneumoniae）属于革兰氏阴性菌，杆状，有大量黏性的多糖形成的荚膜包覆。克雷伯氏肺炎菌可以在人类，特别是免疫力低弱的个体造成肺炎、尿路感染、菌血症等等感染症。然而除了院内感染之外，近年来社区型感染也渐渐增加。在**的糖尿病病患中，克雷伯氏菌经常是造成肝脓疡（liver abscess）的病源。 克雷伯氏菌可以进行乳糖发酵，属于兼性厌氧生物，它是目前柠檬酸发酵被研究的最清楚的微生物。

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 and animal lungs if aspirated (inhaled), specifically to the alveoli (in the lungs) 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, Klebsiella species have become important pathogens in nosocomial infections.