Hemophilus influenzae abscess associated with septicemia

Ultrastructural characterization of capsulated Haemophilus influenzae type b and two spontaneous nontypable mutants

Capsulated Haemophilus influenzae type b and two spontaneous mutants (classes I and II variants) were characterized by transmission and scanning electron microscopy. When cells were treated with type b-specific antiserum prior to manipulations for electron microscopy, sectioned capsulated cells had electron-dense, fibrous capsular antigen-antibody complexes around them. In negatively stained preparations, the complexes appeared as electron-transparent zones surrounding cells. In contrast, only residual electron-dense, extracellular material was seen in sectioned, untreated, capsulated cells, and electron-dense "bridges" connected adjacent cells in negatively stained preparations. No extracellular capsular material was seen around the class I and II variants. Characteristic electron-translucent regions were always observed within the cytosol of the class I cells, both in thin sections and by negative staining. These areas were located adjacent to the cell envelope separating the plasma membrane from the dense cytoplasmic matrix. At times, electron-dense, thread-like material extended from the dense cytoplasmic matrix to the plasma membrane. No such regions were seen in the capsulated and class II cells. Class I cells fixed with methanol or suspended in NaCl or phosphate-buffered saline prior to treatment with fluorescein-tagged type b-specific antiserum (FTA reagent) exhibited, by immunofluorescence, patches of capsular antigen along their sides. However, when fixed with glutaraldehyde or OsO4 or suspended in tris-(hydroxymethyl)aminomethane plus Ca2+ buffer prior to treatment with FTA reagent, no patches of capsular antigen were seen. Subsequent exposure of the latter cells to methanol followed by treatment with FTA reagent resulted in the reappearance of the patches of capsular antigen. Thus, in the class I variant the capsular antigen is unlikely to be surface located. Scanning electron microscopy revealed that class I and II variant cells within undisturbed colonies were regularly aligned side-by-side, whereas cells within colonies of the capsulated strain were randomly distributed.

Identification and quantitation of capsular antigen in capsulated and noncapsulated strains of Haemophilus influenzae type b by crossed-immunoelectrophoresis

Sonicated preparations of capsulated Haemophilus influenzae type b, two of its spontaneous mutants, one containing patches of capsules (class I variant) and the other noncapsulated (class II variant), and a noncapsulated strain of H. influenzae type d were analyzed by crossed-immunoelectrophoresis using unadsorbed antiserum to capsulated H. influenzae type b. Twenty common antigens were present in all four cultures. Two type b-specific antigens were also identified in the three H. influenzae type b cultures when antiserum adsorbed with H. influenzae type d sonicates (AdR) was used. One of these, the type b capsular antigen, cross-reacted with an antigen of Bacillus pumilus. Further adsorption of AdR with the B. pumilus sonicate reduced, but did not eliminate, the antibodies to the type b capsular antigen, although all antibodies to B. pumilus were removed. Sonication sheared the type b capsular antigen, resulting in an increase in its electrophoretic mobility in agarose gel. The capsular antigen from all three H. influenzae type b cultures had the same electrophoretic characteristics. Reproducible quantitation of sheared and unsheared capsular antigen was demonstrated by rocket immunoelectrophoresis. As little as 2.5 ng of polyribophosphate pentose was identified and measured. Capsulated H. influenzae type b contained 78 ng of polyribophosphate pentose per mug of cell protein; class I contained 20 ng and class II contained 4 ng. The small amount of type b capsular antigen present in the class II variant may account for its lack of detection in this organism before now.