Effect of neonatal gastrointestinal colonization with cross reacting Escherichia coli on anticapsular antibody production and bacteremia in experimental Haemophilus influenzae type b disease of rats

Effect of Haemophilus influenzae type b conjugate vaccine in combination with peroral immunization with Escherichia coli on experimental otitis media

The protective ability of a conjugated Haemophilus influenzae type b vaccine, ACT-HIB, used singly or in combination with orally administered Escherichia coli, was investigated in a rat model for acute otitis media. The humoral response to ACT-HIB was also analyzed. The study demonstrated that ACT-HIB vaccination resulted in a prompt antibody response, and that ACT-HIB was efficient in preventing middle ear infections caused by Haemophilus influenzae type b. The efficiency increased if the vaccine was combined with Escherichia coli. The results suggest that Escherichia coli could possibly be useful in the future as a vaccine vehicle, and since Haemophilus influenzae acute mastoiditis seems to be almost exclusively due to serotype b, the incidence of this infection may be reduced with the conjugated Haemophilus influenzae type b vaccines.

Role of nasopharyngeal colonization with and without bacteremia in the protection of infant rats against Haemophilus influenzae type b challenge

Nasopharyngeal colonization of infant rats with Haemophilus influenzae type b was investigated by two methods of intranasal inoculation. After traumatic instillation of the bacteria, 100% of the animals became colonized, compared with 75.5% of animals after atraumatic instillation. Among colonized rats, significantly more animals in the traumatic group developed bacteremia compared with those in the atraumatic group. Rats in the traumatic group had an onset of bacteremia at a mean of 2.6 days after inoculation compared with 7.3 days in the atraumatic group. The duration of colonization and bacteremia was the same in both groups. The majority of heavily colonized rats developed bacteremia compared with none of the lightly colonized rats. Thus, the development of bacteremia appeared to be related independently to both heavy colonization and traumatic instillation. Protection against intraperitoneal bacterial challenge with H. influenzae type b developed in rats that had been bacteremic; in the majority of animals, this correlated with the development of serum bactericidal activity. Protection and bactericidal activity were only rarely observed in nonbacteremic rats that had been either heavily or lightly colonized. The development of serum bactericidal activity was not related to either the duration or peak level of bacteremia. Thus, in this rat model, H. influenzae type b nasopharyngeal colonization without bacteremia did not appear to stimulate circulating antibodies that protected the animals against challenge.

Experimental meningitis in the rat: Haemophilus influenzae

Leptomeningitis due to type b Haemophilus influenzae can be produced in infant rats (up to three weeks of age) by intranasal inoculation, and in animals up to three months of age by intraperitoneal inoculation. In infant animals, the pathogenesis appears to mimic the disease in human infants. Immunologic experiments indicate that antibody directed against the type b capsule (actively or passively acquired) will protect against bacteremia (by any route of inoculation) and the subsequent development of meningitis. However, antibody directed against other surface structures of H. influenzae b (alone or with anticapsular antibody) will protect against sustained bacteremia after any route of inoculation. Evaluation of antibiotic activity against this infection in rats is unreliable due to a marked age-dependent increase in antibiotic clearance. A means of mimicking human pharmacokinetics in rats is proposed. The rat model is useful for the study of H. influenzae meningitis provided certain limitations are recognized.

Clinical uses of microorganisms and their products

Although antibiotics and conventional vaccines are the two most familiar examples of man's exploitation of microorganisms as clinical allies, microorganisms and their products are assuming an increasingly prominent role in the diagnosis, treatment and prevention of human diseases. This report attempts to give a brief overview of the status of the use of microorganisms in clinical medicine and to identify potentially fertile areas for future progress in their clinical application, concentrating on areas other than the already extensively reviewed ones of antibiotics and classic immunization.

Association between cross-reacting Escherichia coli K100 and disease caused by Haemophilus influenzae type b

An unexpected association between Haemophilus influenzae type b (HIB) disease and simultaneous intestinal colonization with cross-reacting Escherichia coli K100 strains is reported. E. coli K100 were found in 18 of 92 (19.5%) HIB patients, compared with 2.5% in healthy individuals of comparable age and in none of 21 patients with meningitis caused by other bacteria. There was no difference in disease outcome, serum antibodies, and circulating HIB antigen between the E. coli K100-positive and -negative HIB patients. Possible explanations and implications of this association are discussed.

Further studies on the immunology of the infant rat experimental model of Haemophilus influenzae type B meningitis

An age-related acquisition of anticapsular (AC) antibodies to Haemophilus influenzae b (HIb) did not occur in rats; this result corrects a previous spurious observation from this laboratory. Purified HIb polysaccharide was found to be totally non-immunogenic over a wide range of doses in infant and adult rats, with or without booster immunizations. Killed HIb was also totally non-immunogenic. Only about one-quarter of survivors of infantile HIb disease made an AC antibody response. In an attempt to observe “immune paralysis”, survivors of infantile HIb disease were immunized with live HIb at age 8 weeks. This immunization resulted in significantly fewer AC antibody responders in the survivors than in the controls. However, immunization of survivors with killed HIb produced significantly greater responders in survivors than in controls. In order to determine whether passive protection from HIb disease could be achieved by non-capsular antibodies, survivors' offspring were studied and found to be protected from infantile HIb disease due to bactericidal (BA) antibodies that were probably not directed at the capsular polysaccharide. Using the BA assay, differences were observed between two HIb strains, presumably due to differences in non-capsular antigens.

The infant rat experimental model of HIb disease appears to have only limited value in the study of AC antibody responses since infant rats differ from infant humans in several respects. The model may be more useful in studying the immunology of non-capsular HIb antigens including their role in protective immunity and possible differences in these antigens among strains of HIb.

Significance of noncapsular antigens in protection against experimental Haemophilus influenzae type b disease: cross-reactivity

A bacterial strain, tentatively identified as an Actinobacillus species, was found to asymptomatically colonize the pharynx of some rats and to bear cell wall antigens which cross-react with noncapsular antigens of Haemophilus influenzae type b (HIb). The cross-reacting antigens appeared to be a heterogeneous mixture with varying molecular size and charge. The antigenic moieties are probably carbohydrate in nature. Antisera raised with this strain had both immunochemical and biological (bactericidal, opsonizing, and protective against experimental infection) activity against HIb. These findings lend further evidence to the idea that noncapsular antigens are important in the induction of resistance to HIb disease. The findings also raise the possibility of using bacteria which cross-react with noncapsular antigens for immunization against HIb disease in humans through nasopharyngeal or enteric colonization.

Experimental Haemophilus influenzae type b meningitis: immunological investigation of the infant rat model

Infant rats inoculated intraperitoneally with Haemophilus influenzae type b develop bacteremia and meningitis. Rats were infected at 10 to 12 days of age and studied for the development of serum anticapsular antibody and bactericidal and opsonizing activity. Seven and 11 weeks after inoculation, convalescent animals showed a higher frequency of anticapsular antibody responses than uninfected controls, but 35 to 40% of the infected group had undetectable levels of anticapsular antibody (<0.10 mug/ml). In contrast, all of the convalescent animals, but none of the controls, showed moderate titers of serum bactericidal activity; and bactericidal activity persisted after absorption of the convalescent sera with type b capsule. Bactericidal activity was detected primarily in the eluted fraction corresponding to a molecular weight of 150,000 and was present in the offspring of convalescent females. Offspring of convalescent females were protected against challenge with H. influenzae type b, and control offspring could also be protected by passive immunization with convalescent serum which lacked detectable anticapsular antibody. Convalescent serum samples efficiently opsonized H. influenzae type b, and this activity persisted after absorption of the serum with capsular antigen. These data are consistent with the hypothesis that antibody to the noncapsular surface antigens of H. influenzae type b play an important role in host defenses.