In vitro and in vivo morphological response of Klebsiella pneumoniae to cefotiam and cefazolin

The effect of cefotiam and cefazolin on the ultrastructure of Klebsiella pneumoniae DT-S in vitro and in experimental pneumonia in mice was examined by electron microscopy. The action of both cephalosporins against K. pneumoniae DT-S was bactericidal, and a dose response in the action was definite. At the minimal inhibitory concentration of each cephalosporin, filamentation of the cells was induced and the cytoplasm became sparse during the course of incubation. With elevation of the concentration of the cephalosporins, spheroplasts were formed; they subsequently collapsed. In the lungs of mice, the infecting organisms localized in the alveolar space, and each cell was connected by a threadlike material. A fibrous matrix, located on the cell surface of the infecting organisms, was observed in ultrathin sections. By administration of each cephalosporin to mice, several morphological changes, similar to those noted in vitro, were observed in the infecting organisms.