Klebsiella pneumoniae bacteria. Computer graphic image of Klebsiella pneumoniae (small and rod- shaped) encapsulated by a thin (yellow) mucous coat. Some red blood cells (larger and yellow) are also seen. Klebsiella is a genus of bacteria of the family Enterobacteriaceae. They are short, plump, Gram-negative bacteria that form capsules. They are often associated with respiratory infection and may cause urinary tract infections. Klebsiella pneumoniae causes pneumonia, inflammation of the lungs, and is found as a secondary invader in infections such as bronchitis or sinusitis. Magnification: x3500 at 6x4.5 cm size.