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

Identification of Haemophilus influenzae type b by a monoclonal antibody coagglutination assay

A coagglutination assay using monoclonal antibody is described for the identification of Haemophilus influenzae type b. An immunoglobulin G2a monoclonal antibody, Hb-2, directed against a serotype-specific outer membrane protein of H. influenzae type b was adsorbed to Staphylococcus aureus Cowan 1 cells. In a dot enzyme immunoassay, Hb-2 reacted with 453 of 455 H. influenzae type b isolates and did not react with H. influenzae of other serotypes, untypeable H. influenzae strains, or other bacterial species. The Hb-2 coagglutination assay was evaluated by testing 136 H. influenzae type b strains selected on the basis of multilocus enzyme genotypes, 5 strains of another serotype, and 94 untypeable H. influenzae strains. The specificity of the coagglutination assay was demonstrated by the inhibition of the reaction by free Hb-2 monoclonal antibodies. The coagglutination assay was as specific as the dot enzyme immunoassay and can be rapidly performed and easily interpreted.

Capsular variation in experimental strains of Haemophilus influenzae

This study sought to demonstrate that clinically untypable strains of Haemophilus influenzae are derivable from previously capsulated ones. Penicillin-induced forms were employed to explore in vivo and in vitro a possible mechanism of the reversible cycle vegetative to L-phase revertant. Normal H. influenzae type b (Rab), capsule-deficient strain ATCC 9333, and experimental L-phase and its revertants were used in this investigation. Capsular antigens, polyribose phosphate (PRP) content of each strain was assayed by orcinol and rocket immunoelectrophoretic methods. Intra- and inter-strain PRP differences were statistically analysed. Strain differences between in vivo and in vitro passaged extracts of strain 9333 and 9333 were significant (t-test P less than 0.01). There were also significant differences in vivo and in vitro between penicillin-treated, L-phase infected mouse isolates and penicillin-free, L-phase infected mouse isolates; and also between penicillin-treated, L-phase infected mouse isolates and revertant Rab infected mouse isolates (Mann-Whitney U-test P less than 0.02, P less than 0.01, respectively). These findings suggest that untypable isolates of H. influenzae are derivable from otherwise capsulated strains, depending on decapsulating factors in the microenvironment. Clinical implications of the findings are discussed.

Identification of immunogenic outer membrane proteins of Haemophilus influenzae type b in the infant rat model system

Outer membrane proteins of Haemophilus influenzae type b which are immunogenic in infant rats were identified by a radioimmunoprecipitation method. Intact cells of H. influenzae type b were radioiodinated by a lactoperoxidase-catalyzed procedure, and an outer membrane-containing fraction was prepared from these cells. These radioiodinated outer membranes were mixed with sera obtained from rats convalescing from systemic H. influenzae type b disease induced at 6 days of age, and the resultant (antibody-outer membrane protein antigen) complexes were extracted from these membranes by treatment with nonionic detergent and ethylenediaminetetraacetic acid. These soluble antibody-antigen complexes were isolated by means of adsorption to protein A-bearing staphylococci, and the radioiodinated protein antigens were identified by gel electrophoresis followed by autoradiography. Infant rats were shown to mount a readily detectable antibody response to several different proteins present in the outer membrane of H. influenzae type b. Individual infant rats were found to vary both qualitatively and quantitatively in their immune response to these immunogenic outer membrane proteins.

Cross-reactions between Haemophilus influenzae and nineteen other bacterial species

Forty-one different antigens were demonstrated in an antigen preparation obtained by sonication of a Haemophilus influenzae (H. influenzae) type b strain, using crossed immunoelectrophoresis and antiserum obtained from rabbits. Antigens were characterized by absorption experiments with whole heat-killed bacteria, temperature resistance and protein and polysaccharide staining. Cross-reactions between H. influenzae type b and 19 other bacterial species were studied by various quantitative immunoelectrophoretic methods, using the reference system. A non-capsulated H. influenzae cross-reacted extensively (41 antigens) with H. influenzae type b and Haemophilus parainfluenzae, and Haemophilus haemolyticus showed considerable cross-reactivity with H. influenzae type b (26 and 32 antigens respectively), while antigens from eight other bacterial species cross-reacted to varying degrees with one to five H. influenzae antigens.

Methods for serotyping nasopharyngeal isolates of Haemophilus influenzae: slide agglutination, Quellung reaction, countercurrent immunoelectrophoresis, latex agglutination, and antiserum agar

Nasopharyngeal isolates of H. influenzae were typed by the slide agglutination test, the Quelling reaction, the latex agglutination test, countercurrent immunoelectrophoresis, and the antiserum agar test. These tests gave essentially comparable results, with countercurrent immunoelectrophoresis and latex agglutination being slightly more sensitive. Cross-reactive problems encountered with latex agglutination and the expense of performing countercurrent immunoelectrophoresis or the antiserum agar test made these tests less practical than the slide agglutination test to identify single strains that were already isolated. The Quellung reaction and slide agglutination were the most rapid tests used to type an organism. For mass screening of multiple samples, countercurrent immunoelectrophoresis was the simplest technique. The antiserum agar test was slow but was the best technique to screen nasopharyngeal swab cultures to identify the presence of any encapsulated strains in the mixed flora. Whether any of the above techniques were as sensitive as the immunofluorescence test was not evaluated in this study.

Bactericidal activity of macromomycin, a antitumor antibiotic

Susceptibility testing by the broth dilution method showed that all the gram-positive but only some of the gram-negative bacteria tested were susceptible to the antitumor antibiotic, macromomycin (MCR; NSC 170105). The minimal inhibitory concentration for the susceptible organisms was less than 3 mug/ml. The action of MCR was bactericidal; however, at very high concentrations (50 mug/ml and above) some organisms occasionally escaped death. None of the escaped organisms was resistant to MCR. In combination with other commonly used antibiotics, MCR displayed partial synergy for Pseudomonas aeruginosa (from a minimal inhibitory concentration of >100 to 12.5 mug/ml with 100 mug of chloramphenicol per ml) and for Bacillus pumilus and Staphylococcus aureus (from 1.6 to 0.4 mug/ml and below) with polymyxin B. As with mammalian cells, (125)I-labeled MCR was irreversibly bound to both gram-positive and -negative bacteria. Treatment with trypsin of the (125)I-labeled MCR-exposed cells did not release the bound MCR or reverse its lethal effect. When in solution in a protective buffer at 4 degrees C, MCR was stable for up to 45 days; at 37 degrees C, however, 25% of its bactericidal activity was lost in 72 h. Loss of activity was enhanced 16-fold in the presence of both heated and unheated pooled human sera. Urine had no effect on the activity of MCR.