Klebsiella pneumoniae

Klebsiella pneumoniae is a Gram-negative, non-motile, encapsulated, lactose-fermenting, facultative anaerobic, rod-shaped bacterium. It appears as a mucoid lactose fermenter on MacConkey agar. Although found in the normal flora of the mouth, skin, and intestines, it can cause destructive changes to human and animal lungs if aspirated, specifically to the alveoli resulting in bloody, brownish or yellow colored jelly-like sputum. In the clinical setting, it is the most significant member of the genus Klebsiella of the 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. 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. It is closely related to K. oxytoca from which it is distinguished by being indole-negative and by its ability to grow on melezitose but not 3-hydroxybutyrate. The genus Klebsiella was named after the German microbiologist Edwin Klebs (1834–1913). It is also known as Friedlander's bacillum in honor of Carl Friedländer, a German pathologist, who proposed that this bacterium was the etiological factor for the pneumonia seen especially in immunocompromised individuals such as people with chronic diseases or alcoholics. Community-acquired pneumonia caused by Klebsiella pneumoniae may occasionally be called Friedländer's pneumonia. Illness most commonly affects middle-aged and older men more often than women with debilitating diseases. This patient population is believed to have impaired respiratory host defenses, including persons with diabetes, alcoholism, malignancy, liver disease, chronic obstructive pulmonary diseases, glucocorticoid therapy, kidney failure, and certain occupational exposures (such as papermill workers).