Fine structures of the capsules of Klebsiella pneumoniae and Escherichia coli K1

Abstract

The fine structures of the capsules of Klebsiella pneumoniae and Escherichia coli were determined by the rapid-freezing technique. The capsular layer was seen as a densely packed accumulation of fine fibers. The thickness of the capsule was approximately 160 nm in K. pneumoniae and less than 10 nm in E. coli Kl. Two layers were observed in the Klebsiella capsule in which the arrangements of the fibers were different. The inner layer of the capsule was formed by a palisade of thick and dense bundles of the fibers standing at right angles on the surface of the outer membrane. In the outer layer these thick bundles of fibers loosened into fine fibers which spread over the bacterial surface, forming a fine network structure.The bacterial species that cause invasive infection usually have a capsule as a virulence factor (4,6,9,10,12). The capsule is said to act as an antiphagocytic factor or to give serum-resistance characteristics to the bacteria. The detailed mechanisms of this action are not known yet, though much information about the capsules is accumulating from chemical, physiological, and immunological studies (7,10,14,16). We assumed that this ambiguity about the role of the capsule in infection was due largely to insufficient knowledge about the functional structures of the capsules. The electron microscope, which has made possible great progress in our knowledge about the morphology of the bacterial cell, has been absolutely useless for examining capsular structures. This is due mostly to the very fragile nature of the bacterial capsule. During the processing for electron microscopy, major parts of the capsular structure are destroyed. Several efforts have been made to observe the fine structures of the capsules by the conventional chemical fixation method, and the structures have been demonstrated only in bacteria expressing relatively thick capsules under careful fixations (3, 9). Recently, however, a milder fixation method has been developed and applied to the observation of bacterial cell structures. This method has dramatically improved the preservation of the fine structures of bacterial cells (2,5,15). With this technique we have demonstrated the presence of a very thin capsule of Vibrio vulnificus (2). In this communication we describe the results of using this technique to reveal the fine structures of the capsules of Klebsiella pneumoniae and Escherichia coli.The bacterial strains used were a capsulated strain, K, of K. pneumoniae and a Kl-positive strain of E. coli. The strain of K. pneumoniae was obtained from our culture stock, and that of E. coli was from R. Sakazaki of The National Institute of Health, Tokyo, Japan. The presence of the capsule of K. pneumoniae was revealed by the Hiss capsular staining method. This strain is highly virulent to mice. Less than 10 CFU of bacteria injected peritoneally is sufficient to kill the animals. The strain of E. coli is of 02:K1:H2 serotype. The capsule, Kl antigen, of this strain was not visible under the light microscope after capsular staining. These...

Characterization of outer membrane vesicles released by the psychrotolerant bacterium Pseudoalteromonas antarctica NF3

“…For P. antarctica cells, the presence of an inner layer of oriented packed fibres extending perpendicularly away from the cell envelope, as well as an outer layer of randomly distributed fine fibres could be regarded as a capsule. These two polymeric arrangements have also been reported for capsules from Escherichia coli K1 and Klebsiella pneumoniae K (Amako et al ., 1988). Other encapsulated bacteria have been observed by TEM following HPF‐FS (Graham et al ., 1991; Korenevsky et al ., 2002).…”

Mechanism of Enhancement of Bactericidal Activity of Phagocytes against <i>Klebsiella pneumoniae </i>Treated with Subminimal Inhibitory Concentrations of Cefodizime

“…The surface of normal K. pneumo niae was covered with a very thick fibrous cap sular material layer (160 nm). The findings were similar to the capsular material of K. pneumoniae fixed by a rapid-freezing tech nique reported by Amako et al [12], by which the capsular material can be observed in its most natural state. After treatment with cefpimizole, which had the lowest bactericidal activity, the bacteria became filamentous, and the thickness of the capsular material layer was thinner (90 nm) than that of the normal bacte ria.…”

Current status of meningococcal group B vaccine candidates: capsular or noncapsular?

“…The complete capsule is about 10 nm thick. This thickness is notably less than that of other capsules: e.g., Klebsiella pneumoniae, with a similar layout, is about 160 nm thick (10). However when the E. coli Kl capsule was stabilized with antibodies, much higher values for the capsular thickness were obtained, i.e., >300 nm (115).…”

“…By this technique, the capsule of E. coli Ki has been observed to consist of two layers, an inner and an outer one (10). The fibrous material of the inner layer forms a dense stratum which is probably made up of a series of thick bundles set perpendicular to the outer membrane surface.…”