The nasopharyngeal microflora of otitis-prone children, with emphasis on H. influenzae

Nontypeable Haemophilus influenzae Redox Recycling of Protein Thiols Promotes Resistance to Oxidative Killing and Bacterial Survival in Biofilms in a Smoke-Related Infection Model

Smoke exposure is a risk factor for community-acquired pneumonia, which is typically caused by host-adapted airway opportunists like nontypeable Haemophilus influenzae (NTHi). Genomic analyses of NTHi revealed homologs of enzymes with predicted roles in reduction of protein thiols, which can have key roles in oxidant resistance. Using a clinical NTHi isolate (NTHi 7P49H1), we generated isogenic mutants in which homologs of glutathione reductase (open reading frame NTHI 0251), thioredoxin-dependent thiol peroxidase (NTHI 0361), thiol peroxidase (NTHI 0907), thioredoxin reductase (NTHI 1327), and glutaredoxin/peroxiredoxin (NTHI 0705) were insertionally inactivated. Bacterial protein analyses revealed that protein oxidation after hydrogen peroxide treatment was elevated in all the mutant strains. Similarly, each of these mutants was less resistant to oxidative killing than the parental strain; these phenotypes were reversed by genetic complementation. Analysis of biofilm communities formed by the parental and mutant strains showed reduction in overall biofilm thickness and density and significant sensitization of bacteria within the biofilm structure to oxidative killing. Experimental respiratory infection of smoke-exposed mice with NTHi 7P49H1 showed significantly increased bacterial counts compared to control mice. Immunofluorescent staining of lung tissues showed NTHi communities on lung mucosae, interspersed with neutrophil extracellular traps; these bacteria had transcript profiles consistent with NTHi biofilms. In contrast, infection with the panel of NTHi mutants showed a significant decrease in bacterial load. Comparable results were observed in bactericidal assays with neutrophil extracellular traps in vitro. Thus, we conclude that thiol-mediated redox homeostasis is a determinant of persistence of NTHi within biofilm communities.

IMPORTANCE Chronic bacterial respiratory infections are a significant problem for smoke-exposed individuals, especially those with chronic obstructive pulmonary disease (COPD). These infections often persist despite antibiotic use. Thus, the bacteria remain and contribute to the development of inflammation and other respiratory problems. Respiratory bacteria often form biofilms within the lungs; during growth in a biofilm, their antibiotic and oxidative stress resistance is incredibly heightened. It is well documented that redox homeostasis genes are upregulated during this phase of growth. Many common respiratory pathogens, such as NTHi and Streptococcus pneumoniae, are reliant on scavenging from the host the necessary components they need to maintain these redox systems. This work begins to lay the foundation for exploiting this requirement and thiol redox homeostasis pathways of these bacteria as a therapeutic target for managing chronic respiratory bacterial infections, which are resistant to traditional antibiotic treatments alone.

Dynamics of Nasopharyngitis in Children

PURPOSE: Our goal was to characterize the dynamics and bacterial interaction of the aerobic and anaerobic flora of nasal discharge of children at different stages of uncomplicated nasopharyngitis.

METHODS AND PATIENTS: Serial semiquantitative nasopharyngeal (NP) and quantitative nasal discharge (ND) cultures were taken every 3 to 5 days from 20 children in whom purulent discharge eventually developed (group 1), and a single culture was obtained from a group of 20 who had only clear discharge (group 2).

RESULTS: Aerobic and anaerobic bacteria were isolated from all NP cultures. Bacterial growth was present in 8 (40%) NDs of group 2. Only 7 (35%) of the clear NDs of group 1 showed bacterial growth; the number increased to 14 (70%) at the mucoid stage and 20 (100%) at the purulent stage. It declined to 6 (30%) at the final clear stage. The number of species and total number of organisms increased in the NDs of group 1. Group 1 patients had higher recovery rates of Streptococcus pneumoniae and Haemophilus influenzae in their NP cultures than group 2 patients (P > 0.05). During the purulent stage, Peptostreptococcus species were isolated in 15 (75%), Fusobacterium species in 10 (50%), Prevotella species in 9 (45%), H influenzae in 8 (40%), S pneumoniae in 6 (30%), and β-hemolytic streptococci in 5 (25%) of group 1 NDs. This was higher than their recovery in the clear stages of both groups and the mucoid stage of group 1. A total of 8 organisms capable of interfering with the growth of potential pathogens were isolated from the NPs of group 1, as compared with 35 from group 2 ( P > 0.001).

CONCLUSIONS: The development of purulent nasopharyngitis is associated with the pre-existing presence of potential pathogens and the absence of interfering organisms.

Eustachian tube gland tissue changes are related to bacterial species in acute otitis media

BACKGROUND AND OBJECTIVE

Prior investigations have shown that the number of mucus producing goblet cells in the middle ear and Eustachian tube (ET) mucosa is highly increased during and up to at least six months after experimental acute otitis media (AOM) caused by Streptococcus pneumoniae (SP). Further, the volume of the mucus producing paratubal gland components is increased up to 3 months after the acute infection. These changes may in conjunction with a deteriorated ET function predispose a subsequent development of secretory otitis media. The present investigation compares changes in goblet cell density and gland structures of the ET during and after AOM caused by various bacteria typically encountered in this disease, with emphasis on potential differences due to bacterial species.

METHODS

Rat models of AOM caused by SP, non-typeable or type b Haemophilus influenzae (NTHI/HIB) or Moraxella catarrhalis (MC) were studied longitudinally up to 6 months after bacterial challenge. The ET was dissected and decalcified, paraffin embedded and serially sectioned, followed by PAS/alcian blue staining. The goblet cell density and the paratubal gland composition and volume were determined morphometrically in every 20th section, using a light microscope.

RESULTS

Regardless of bacterial species, the ET goblet cell density was increased from day 8 and peaked day 16, followed by some degree of normalisation, although not reaching normal numbers within the 6 month period, except for MC. The highest increase was seen in AOM caused by the non-typeable Haemophilus strain, followed by HIB, SP and MC. Except with MC, pathological intra-epithelial glands formed and goblet cells were found in mucosal areas normally devoid of these. In all species but MC, the volume of the paratubal glands progressed to peak 16 days post-inoculation, followed by a gradual normalisation. The volume was still increased 3 months after the acute infection, but completely normalised after 6 months. The increase was primarily due to hypertrophy of the mucous gland components and highest in AOM caused by the Haemophilus species, followed by SP.

CONCLUSION

The Eustachian tube goblet cell density is increased during and up to at least six months after AOM regardless of bacterial species, except when employing MC, by which the density was increased for a few weeks only. Except in AOM caused by MC, the volume of the ET glands increases during and up to at least 3 months after infection, primarily due to hypertrophy of the mucous gland components. The non-typeable Haemophilus strain induced the highest increase of both goblet cell density and mucous gland volume. The increased secretory capacity of the ET following AOM may by excessive mucus secretion contribute to the deteriorated ET function found after AOM and thus predispose, sustain or aggravate middle ear disease.

Microbial dynamics of purulent nasopharyngitis in children

This review presents the microbiological dynamic and therapeutic options in the management of purulent nasopharyngitis (NPT). The nasopharynx (NP) of healthy children is generally colonized by relatively non-pathogenic aerobic and anaerobic organisms, some of, which possess the ability to interfere with the growth of potential pathogens. Conversely, carriage of potential respiratory aerobic pathogen such as Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis, as well as some anaerobic bacteria (Peptostreptococcus, Fusobacterium and Prevotella spp.) increases during purulent NPT. The development of purulent NPT in children is associated with the pre-existing colonization by potential pathogens and the absence of interfering organisms in the NP. Controversy exists regarding the management of NPT as no conclusive evidence exists to date that the administration of antimicrobials will shorten the illness.

Differences in nasopharyngeal bacterial flora in children with nonsevere recurrent acute otitis media and chronic otitis media with effusion: implications for management

BACKGROUND

The interactions between nasopharyngeal flora and the individual entities covered by the broad term otitis media have not been completely elucidated. We investigated in infants and children ages 6 months to 7 years with nonsevere recurrent acute otitis media (rAOM) or with chronic otitis media with effusion (cOME): (1) the nasopharyngeal carriage rate and bacterial density of respiratory pathogens and alpha-hemolytic streptococci in comparison with healthy children; (2) the resistance pattern of respiratory pathogens; and (3) the relationship between the type of nasopharyngeal colonization and long term outcome.

METHODS

Nasopharyngeal cultures were obtained from 85 children with rAOM,113 children with cOME and 55 controls. A semiquantitative analysis was used in the reading of cultures. A 12-week follow-up without treatment was planned.

RESULTS

The carrier rate of respiratory pathogens was significantly greater in cOME (70%) than in rAOM (45%) (P = 0.0006) or controls (31%) (P < 0.0001). Similarly colonization density was significantly greater in cOME than in rAOM. The carriage rate and the colonization density of alpha-hemolytic streptococci were significantly lower in rAOM than in cOME or controls. The incidence of resistant (R) strains was greater in rAOM (Streptococcus pneumoniae penicillin-R, 24%; macrolide-R, 64%; Haemophilus influenzae amoxicillin-R, 24%) compared with cOME (S. pneumoniae penicillin-R,18%; macrolide-R, 44%; H. influenzae amoxicillin-R, 5%) or controls (S. pneumoniae penicillin-R, 8%; macrolide-R, 23%; H. influenzae amoxicillin-R, 10%). During the follow-up period persistence of OME and occurrence of AOM were greater among carriers of respiratory pathogens at baseline.

CONCLUSIONS

There are substantial differences in nasopharyngeal flora between children with nonsevere rAOM and children with cOME. The results of nasopharyngeal cultures should be taken into account to avoid treatment with drugs that are ineffective and likely to select resistant organisms.

Histopathologic differences due to bacterial species in acute otitis media

OBJECTIVE

To compare selected features of histopathology in acute otitis media caused by various bacteria and examine potential differences due to bacterial species, as well as possible correlation to experimental and human clinical findings.

METHODS

Rat models of acute otitis media caused by Streptococcus pneumoniae (MC), non-typeable or type b Haemophilus influenzae (NTHI/HIB) or Moraxella catarrhalis (MC) were studied longitudinally up to 6 months after bacterial challenge. Findings related to dynamics of goblet cell density, modeling and remodeling of bone tissue structures and polyp, as well as fibrous adhesion formation and persistence are presented.

RESULTS

Middle ear goblet cell density progressed to peak 2 weeks after bacterial inoculation, thereafter gradually normalizing. However, density and accordingly middle ear secretory capacity was still significantly increased after 6 months in all bacteria, except MC. The HI species induced the highest increase. Initial osteoresorption was followed by massive osteoneogenesis, progressing to a peak after 2-3 months, followed by some degree of normalization, concurrently classic remodeling. Primarily SP, but also the HI species induced more new bone formation than MC. Mucosal polyp and fibrous adhesion formation occurred regardless of bacterial species. Most polyps appeared in the early phases and the HI species induced formation of more polyps and adhesions than the other bacteria.

CONCLUSION

Acute middle ear infection with the Haemophilus species induce the highest increase of mucosal secretory capacity, lasting for at least 6 months after the acute incident. Thus, a subsequent development of secretory otitis media seems more likely following infection with these bacteria. Equivalently, mucosal scarring observed as polyp and fibrous adhesion formation was more severe following Haemophilus infection. S. pneumoniae induced the most marked changes of bone tissue structures, seen as initial osteoresorption and subsequent osteoneogenesis. Overall, infection with M. catarrhalis induced the mildest changes.

The nasopharynx and the middle ear. Inflammatory reactions in middle ear disease

The host-parasite interactions in the nasopharynx with bacterial colonization and antigen uptake in the lymphoid tissue, the adenoid, has an impact on the maturation of local and systemic immunity. The adenoid is a part of mucosa associated lymphoid tissue and is responsible for both effector and inductor functions in the nasopharynx. Increasing evidence supports the role of serum antibody in protecting the middle ear cavity from disease. There is evidence for a minor immunologic defect in a number of children with recurrent episodes of AOM.

Turnover of Haemophilus influenzae isolates in otitis-prone children

INTRODUCTION

Previous studies have suggested a direct relationship between the nasopharyngeal carriage of potential middle ear pathogens and the development of middle ear disease. It has been shown that otitis-prone (OP) children tend to be colonized more often than non-OP children. To study the turnover of nontypeable Haemophilus influenzae (NTHI) in the nasopharynx of OP children, arbitrarily primed PCR was applied to NTHI strains isolated nasopharyngeal swabs collected prospectively during a 2-year study period from 35 OP children under 4 years of age at fixed intervals. METHODOLOGY/MATERIALS: In 20 patients, H. influenzae could be isolated from different sites (left and/or right ear and/or nasopharynx) or at different occasions during follow-up. Forty-eight H. influenzae isolates of different sites (left and/or right ear and/or nasopharynx) of the same patient as well as from siblings were typed using arbitrarily primed PCR with primer ERIC2 and RAPD Ready-to-Go beads (Pharmacia Biotech, Uppsala, Sweden).

RESULTS

Typing with arbitrarily primed PCR enabled to differentiate 29 genotypes among the 48 H. influenzae isolates. Sixteen of these fingerprints were observed only once. Thirteen of these fingerprints appeared on two or more occasions. In the three pairs of siblings the same strain was identified at one moment. Genetically identical NTHI strains from unrelated individuals were never identified. In 11 of 14 cases for which isolates were obtained simultaneously from different sites (throat and/or left ear and/or right ear) or from three pairs of siblings, identical fingerprints were observed. In nine cases whereby isolation was separated by a period of more than 4 weeks (maximum 28 weeks) the fingerprints of the isolates were different from the original isolate.

CONCLUSION

Typing with arbitrarily primed PCR indicated substantial genetic diversity among the H. influenzae isolates studied, since for a total of 48 isolates of 20 different patients, 29 different genotypes were observed. Since simultaneous isolation for different sampling sites (ear or nasopharynx) as well as for both of siblings, resulted mostly in identical fingerprints, and since sampling of the same site of the same patient, separated by an interval of more than 1 month, almost always resulted in different genotypes, one could conclude that both cross colonization (between sampling sites within the same patient and between siblings) and turnover are high. The relation between acquisition and development of disease needs further attention.

Dynamics of nasopharyngitis in children

PURPOSE

Our goal was to characterize the dynamics and bacterial interaction of the aerobic and anaerobic flora of nasal discharge of children at different stages of uncomplicated nasopharyngitis.

METHODS AND PATIENTS

Serial semiquantitative nasopharyngeal (NP) and quantitative nasal discharge (ND) cultures were taken every 3 to 5 days from 20 children in whom purulent discharge eventually developed (group 1), and a single culture was obtained from a group of 20 who had only clear discharge (group 2).

RESULTS

Aerobic and anaerobic bacteria were isolated from all NP cultures. Bacterial growth was present in 8 (40%) NDs of group 2. Only 7 (35%) of the clear NDs of group 1 showed bacterial growth; the number increased to 14 (70%) at the mucoid stage and 20 (100%) at the purulent stage. It declined to 6 (30%) at the final clear stage. The number of species and total number of organisms increased in the NDs of group 1. Group 1 patients had higher recovery rates of Streptococcus pneumoniae and Haemophilus influenzae in their NP cultures than group 2 patients (P < 0.05). During the purulent stage, Peptostreptococcus species were isolated in 15 (75%), Fusobacterium species in 10 (50%), Prevotella species in 9 (45%), H influenzae in 8 (40%), S pneumoniae in 6 (30%), and beta-hemolytic streptococci in 5 (25%) of group 1 NDs. This was higher than their recovery in the clear stages of both groups and the mucoid stage of group 1. A total of 8 organisms capable of interfering with the growth of potential pathogens were isolated from the NPs of group 1, as compared with 35 from group 2 (P < 0.001).

CONCLUSIONS

The development of purulent nasopharyngitis is associated with the pre-existing presence of potential pathogens and the absence of interfering organisms.

Role of nasopharyngeal bacterial flora in the evaluation of recurrent middle ear infections in children

OBJECTIVE: To study the nasopharyngeal colonization in otitis-prone children before and after adenoidectomy. METHODS: The study population consisted of 35 children between 11 months and 4 years of age, undergoing adenoidectomy and tube placement for recurrent acute otitis media. All these children were otitis prone (OP). During general anesthesia, bacteriologic samples were obtained from the nasopharynx and the middle ear fluid, if present. During the follow-up visit, a new nasopharyngeal culture was taken. The control population consisted of 35 children undergoing surgery for non-ear-nose-throat pathology. These children had no history of recurrent upper respiratory tract infections. RESULTS: Colonization of the nasopharynx with potential pathogens (Streptococcus pneumoniae, Moraxella catarrhalis, Haemophilus influenzae) occurred significantly more in the OP children than in the non-OP children. Adenoidectomy resulted in a substantial decrease of potential middle ear pathogens in the nasopharynx and an increase of normal commensal flora. In about half of the patients, middle ear fluid was still present at the time of tube placement; in most instances, H. influenzae was cultured. Typing with arbitrarily primed PCR indicated substantial genetic diversity among the H. influenzae isolates studied. CONCLUSIONS: Both cross-colonization (between sampling sites within the same patient and between siblings) and turnover appeared to be high.

Protection against development of otitis media induced by nontypeable Haemophilus influenzae by both active and passive immunization in a chinchilla model of virus-bacterium superinfection

Three separate studies, two involving active-immunization regimens and one involving a passive-transfer protocol, were conducted to initially screen and ultimately more fully assess several nontypeable Haemophilus influenzae outer membrane proteins or their derivatives for their relative protective efficacy in chinchilla models of otitis media. Initial screening of these antigens (P5-fimbrin, lipoprotein D, and P6), delivered singly or in combination with either Freund's adjuvant or alum, indicated that augmented bacterial clearance from the nasopharynx, the middle ears, or both anatomical sites could be induced by parenteral immunization with P5-fimbrin combined with lipoprotein D, lipoprotein D alone, or the synthetic chimeric peptide LB1 (derived from P5-fimbrin), respectively. Data from a second study, wherein chinchillas were immunized with LB1 or lipoprotein D, each delivered with alum, again indicated that clearance of nontypeable H. influenzae could be augmented by immunization with either of these immunogens; however, when this adjuvant was used, both antibody titers in serum and efficacy were reduced. A third study was performed to investigate passive delivery of antisera directed against either LB1, lipoprotein D, nonacylated lipoprotein D, or a unique recombinant peptide designated LPD-LB1(f)2,1,3. The last three antiserum pools were generated by using the combined adjuvant of alum plus monophosphoryl lipid A. Passive transfer of sera specific for LB1 or LPD-LB1(f)2,1,3 to adenovirus-compromised chinchillas, prior to intranasal challenge with nontypeable H. influenzae, significantly reduced the severity of signs and incidence of otitis media which developed (P </= 0.001). Collectively, these data indicate the continued merit of further developing LB1 and LPD-LB1(f)2,1,3 as components of vaccines for otitis media.

Mucosal Immunity and Bacteriology of the Eustachian Tube

The pathogenesis of otitis media is a multifaceted process that is not completely understood. Eustachian tube dysfunction plays a central but uncertain role, as do viral and bacterial microorganisms. Of the latter, the three most important are Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis. This article reviews the various mechanisms of infection and the immune system's response to them.

Nasopharyngeal colonization with nontypeable Haemophilus influenzae in chinchillas

Colonization of the nasopharynx by a middle ear pathogen is the first step in the development of otitis media in humans. The establishment of an animal model of nasopharyngeal colonization would therefore be of great utility in assessing the potential protective ability of candidate vaccine antigens (especially adhesins) against otitis media. A chinchilla nasopharyngeal colonization model for nontypeable Haemophilus influenzae (NTHI) was developed with antibiotic-resistant strains. This model does not require coinfection with a virus. There was no significant difference in the efficiency of NTHI colonization between adult (1- to 2-year-old) and young (2- to 3-month-old) animals. However, the incidence of middle ear infection following nasopharyngeal colonization was significantly higher in young animals (83 to 89%) than in adult chinchillas (10 to 30%). Chinchillas that had recovered either from a previous middle ear infection caused by NTHI or from an infection by intranasal inoculation with NTHI were completely protected against nasopharyngeal colonization with a homologous strain and were found to be the best positive controls in protection studies. Systemic immunization of chinchillas with inactivated whole-cell preparations significantly protected animals not only against homologous NTHI colonization but also partially against heterologous NTHI infection. In all protected animals, significant serum anti-P6 and anti-HMW antibody responses were observed. The outer membrane P6 and high-molecular-weight (HMW) proteins appear to be promising candidate vaccine antigens to prevent nasopharyngeal colonization and middle ear infection caused by NTHI.

Adherence of non-typeable Haemophilus influenzae promotes reorganization of the actin cytoskeleton in human or chinchilla epithelial cells in vitro

Non-typeable Haemophilus influenzae (NTHi) are opportunistic mucosal pathogens which adhere to epithelial cells via a variety of non-specific and specific interactions. Several adhesins have been identified and while the complimentary receptor(s) for each of these adhesins has not yet been fully characterized, it is widely accepted that adherence is an absolute prerequisite for disease. Several reports have indicated that NTHi can also be internalized and reside intracellularly. For this to occur, NTHi must be taken up by mucosal epithelial cells lining the respiratory tract. We have noted, by TEM, that adherent NTHi overlie an electron dense area in the cell membrane of human epithelial cells which is associated with a localized complex assembly of cytoskeletal fibers in the eukaryotic cytoplasm. We thus examined the potential involvement of cytoskeletal actin in this phenomenon via FITC-phalloidin labeling of respiratory tract epithelial cells which had been incubated with several clinical isolates of NTHi. Strong punctate fluorescence was coincident with adherent NTHi to both human oropharyngeal and chinchilla middle ear epithelial cells. This reactivity was similar to the discrete fluorescent spots observed with enteropathogenic Escherichia coli which were adhered to HeLa cells. In contrast, none of the NTHi isolates tested induced actin polymerization in cells of endothelial origin. While the exact mechanisms involved are yet to be elucidated, our data indicated that actin nucleation was coincident with NTHi adherence.

Role of adenoids in the pathogenesis of otitis media: a bacteriologic and immunohistochemical analysis

Adenoidectomy is frequently performed in children suffering from recurrent or chronic otitis media with effusion and is thought to produce a long-term effect in preventing further episodes of otitis media. Bacteriologic analysis of adenoids from 60 patients revealed a significantly elevated colonization rate of middle ear pathogens in children with a present or previous history of ear disease compared to children with adenoidal hypertrophy only. The predominant pathogen was nontypeable Haemophilus influenzae, followed by Streptococcus pneumoniae and Moraxella catarrhalis. Quantitative analysis did not demonstrate a bacterial overload in the otitis group. Lectin histochemical analysis of the adenoids revealed no significant differences between the three groups; nevertheless, colonization with S pneumoniae demonstrated an increased labeling pattern with succinylated wheat germ agglutinin, indicating the exposure of N-acetyl-glucosamine as part of its own receptor structure. On the basis of these results, we support the concept of adenoidectomy in order to remove a bacterial focus; however, we could not verify the hypothesis of bacterial overgrowth in the nasopharynx.

The tympanic membrane and middle ear mucosa during non-typeable Haemophilus influenzae and Haemophilus influenzae type b acute otitis media: a study in the rat

Non-typeable Haemophilus influenzae (NTHi) and encapsulated Haemophilus influenzae type b (Hib) were inoculated into the middle ears of Sprague-Dawley rats. Tympanic membrane (TM) status was assessed otomicroscopically and specimens from various middle ear areas were prepared for light microscopy at various times during the acute phase and up to 6 months after inoculation. Irrespective of bacteria strain, acute otitis media (AOM) was present in all ears 4 days after inoculation. The Hib-infected ears showed initially a severe course of AOM, but all were otomicroscopically resolved by day 12, at which time a few NTHi-inoculated ears still exhibited middle ear effusion. The TMs infected with Hib had normalized without scar formation, whereas NTHi induced a persistent thickening of the TMs in half of all cases. The middle ear mucosa of NTHi-infected ears initially showed vigorous activity among the goblet cells, but the mucosa normalized after the acute phase. Hib, by contrast, induced prominent changes in the middle ear mucosa. Initially, no goblet cell granules or ciliated cells could be observed in the mucosa. Later on, the epithelium contained large, active goblet cells. Glands appeared beneath the mucosa which persisted as streaks of epithelial cells throughout the study period. The findings show that NTHi and Hib both induce AOM but with differing clinical courses, and affect different targets in the middle ear.

Immunoglobulin G Subclass Response to Major outer Membrane Proteins of Nontypable Haemophilus Influenzae in Children with Acute Otitis Media

Children with acute otitis media as the result of nontypable Haemophilus influenzae often develop serum bactericidal and/or opsonic IgG antibodies to this organism during convalescence. Outer membrane proteins appear to be the principal targets for such antibodies. In this study we characterized the IgG subclass responses to major outer membrane proteins of nontypable H. influenzae in otitis-prone children in whom this organism had colonized. Three of the major outer membrane proteins (P2, P5, and P6) were isolated from the homologous nontypable H. influenzae strain recovered from the middle ear at the time of acute infection. Sera were obtained during the acute phase and at 1 and 6 months thereafter. The outer membrane proteins, which were isolated by preparative sodium dodecylsulfate-polyacrylamide gel electrophoresis, were used as test antigens in a quantitative IgG subclass enzyme immunoassay. The results of this analysis indicate that the temporal characteristics and distribution of IgG subclass antibodies were found to differ for each of the outer membrane proteins. Moreover, substantial variation between patients was observed with respect to both temporal characteristics and subclass distribution of the IgG response to the three outer membrane proteins. Significantly, sera from two of three otitis-prone subjects contained detectable levels of IgG antibody to the conserved P6 outer membrane protein at the time of acute infection, with serum from one subject also containing detectable levels of lgG3 antibody to this same protein. Nevertheless, the organism persisted in the middle ears of these patients. The results of this study indicate that otitis-prone children manifest a highly variable IgG subclass response to both conserved (P6) and variable (P2) outer membrane proteins of nontypable H. influenzae. Further study is required to ascertain whether these IgG subclass antibodies are biologically efficacious and whether otitis-prone children possess the immunologic maturity to respond to nontypable H. influenzae outer membrane protein-based vaccines in a predictable manner.

Are there microbiological markers to predict recurrent acute otitis media?

The nasopharynx is a natural reservoir for several bacterial species, including Streptococcus pneumoniae and Haemophilus influenzae. Carriership is a potential mechanism for pathogenicity, since bacteria might invade the Eustachian tube and cause middle ear disease. Whether the pattern of nasopharyngeal colonization is different in infection prone vs healthy children is still a matter of controversy. In several studies it has been shown that H. influenzae is carried significantly more often in otitis-prone children compared with healthy control children. Colonization with H. influenzae in young children may be regarded as a candidate for a microbiological marker for recurrent episodes of acute otitis media.

Persistence of nontypeable Haemophilus influenzae in adenoid macrophages: a putative colonization mechanism

That nontypeable H. influenzae (NTHI) can reside intracellularly in human adenoid tissue has been suggested by use of in situ hybridization of a fluorescein labelled 16S rRNA-targeted oligonucleotide probe (FISH). Adenoid tissues from 43 children operated on in a clinically infection-free interval were investigated. FISH revealed H. influenzae in macrophage-like cells, located subepithelially in the crypts in all 43 adenoids. Furthermore, H. influenzae was detected in 22/22 adenoids using immunohistochemistry with the monoclonal antibody MAHI-3 recognizing a conserved H. influenzae LPS inner-core region. FISH and staining with monoclonal antibodies against immunophenotypic markers were performed simultaneously in order to characterize the cellular interrelations in this microenvironment. The findings of widespread presence of H. influenzae in cells of which some strongly expressed the CD14 marker of the monocyte/macrophage lineage may correspond to an important aspect of the colonization mechanisms whereby NTHI persists in the nasopharynx of children.

High incidence of Haemophilus influenzae in nasopharyngeal secretions and middle ear effusions as detected by PCR

PCR was used to detect Haemophilus influenzae in samples of nasopharyngeal secretion and middle ear effusion (MEE). Nasopharyngeal secretions were collected from 102 patients with otitis media with effusion and from 111 healthy subjects. Eighty samples of MEE were collected from patients with otitis media with effusion. A pair of primers was designed to amplify a DNA segment of the gene encoding P6 outer membrane protein of H. influenzae. The amplified PCR product was detected with an internal probe that hybridized specifically to the P6 DNA of H. influenzae. Samples of MEE and nasopharyngeal secretion were also examined by a conventional culture method. The incidence of P6 gene DNA in nasopharyngeal secretions detected by PCR was about two times higher than that of H. influenzae detected by the conventional culture. Culture-positive samples were all positive in the PCR test. In MEEs, the rate of detection of the P6 gene DNA target was about five times higher than that of H. influenzae detected by the culture method. All patients who had P6 gene DNA in MEEs were found to have the DNA in nasopharyngeal secretions. These findings suggest that the presence of H. influenzae in MEEs and in nasopharyngeal secretions is more common than previously reported.

Immunological aspects of otitis media: present views on possibilities of immunoprophylaxis of acute otitis media in infants and children

The article reviews, based on current knowledge of immunological events affecting the middle ear, the possibilities and prospects for the prevention of otitis media (OM) by immunologic measures. While pneumococcal capsular polysaccharide vaccines proved not to be effective against infant acute otitis media (AOM), pneumococcal conjugate vaccines provide good immunogenicity even in infants, and call for trials with better prospects of clinical efficacy. The other future approaches currently under development are vaccines against nontypable Haemophilus influenzae and Branhamella catarrhalis, anti-viral immunoprophylaxis, combinations of the above alternatives, or passive immunization. Also, the use of new routes or ways of immunization are under study. Furthermore, the ways to modify the present treatment practices of AOM to favour good immunologic responses in infants and children must be studied.

Cytokines in nasopharyngeal secretions; evidence for defective IL-1 beta production in children with recurrent episodes of acute otitis media

The host-parasite relationship in the nasopharynx of young children with bacterial colonization and antigen uptake in the mucosa and lymphatic tissue provides an opportunity to investigate infectious/inflammatory processes and responses. IL-1 beta, IL-6 and tumour necrosis factor-alpha (TNF-alpha) were analysed in nasopharyngeal secretions and serum from children with or without recurrent episodes of acute otitis media, from healthy adults and adults with or without recurrent episodes of acute otitis media, from healthy adults and adults with hypogammaglobulinaemia or selective deficiency of IgG3. Nasopharyngeal secretions generally contained substantial amounts of IL-1 beta, IL-6 and TNF-alpha. In contrast, IL-1 beta, IL-6 and TNF-alpha were not detectable in sera on the same occasion. Children were found to have higher levels of IL-1 beta, IL-6 and TNF-alpha than healthy adults and than adults with immunodeficiency. High levels of IL-1 beta were associated with low or undetectable levels of IL-6 and TNF-alpha, whereas the opposite pattern was seen in association with low levels of IL-1 beta. This was especially true for children with recurrent episodes of acute otitis media (RAOM). In children with nasopharyngeal colonization with Haemophilus influenzae, significantly higher levels of IL-1 beta, IL-6 and TNF-alpha (P = 0.0001, respectively) were found compared with non-colonized children. Notably, the RAOM children exhibited significantly lower levels of IL-1 beta, IL-6, and TNF-alpha in nasopharyngeal secretions (P = 0.0001, 0.01 and 0.0001, respectively) than healthy children. These results demonstrate local production of inflammatory cytokines in nasopharynx, related to bacterial colonization, and suggest that children with RAOM are poor nasopharyngeal cytokine producers.

The nasopharynx, eustachian tube and otitis media

It has been classically hypothesized that a mass in the nasopharynx causes an obstacle to air flow through the eustachian tube, thereby creating a negative pressure in the middle ear followed by an effusion. However, examination of the relevant data concerning the supposed obstruction of the eustachian tube by nasopharyngeal carcinomas, choanal polyps and adenoids does not seem to support this cause and effect relationship. Evidence points to other more sophisticated mechanisms which cause negative pressure and an effusion in pathological middle ear conditions. While the hypothesis of a nasopharyngeal mass as the usual obstructive cause of middle ear effusion is hard to maintain, evidence does exist to support the origin of middle ear infection, as seen in acute and secretory otitis media, as being associated, at times, with an ascending infection from the nasopharynx.

Human milk secretory IgA antibody to nontypeable Haemophilus influenzae: possible protective effects against nasopharyngeal colonization

Sixty-eight children fed human milk were followed prospectively from birth to 12 months of age to assess the effect of milk antibody on nasopharyngeal colonization. Human milk secretory IgA antibody to P6, a highly conserved outer membrane protein of nontypeable Haemophilus influenzae, was measured with the use of an enzyme-linked immunosorbent assay. Nasopharyngeal colonization with nontypeable H. influenzae and the occurrence of otitis media were determined. Nasopharyngeal colonization was found in 22 children (32%), and 39 children (57%) had otitis media. Frequency of isolation of nontypeable H. influenzae was directly related to episodes of otitis media (r = 0.35; p = 0.001). The level of human milk anti-P6 secretory IgA antibody was inversely related to frequency of isolation of the organism (r = -0.27; p = 0.026). The average antibody level, expressed as nanograms per 0.1 mg total secretory IgA, in human milk fed to children with no colonization of nontypeable H. influenzae was significantly higher than in milk fed to children in whom colonization occurred on multiple occasions (156 +/- 120 vs 69 +/- 50; p = 0.013). Prevention of colonization was most evident during breast-feeding. These data suggest that the protective effects of human milk against otitis media may be due in part to inhibition of nasopharyngeal colonization with nontypeable H. influenzae by specific secretory IgA antibody.

Adult bacterial nasopharyngitis: a clinical entity?

OBJECTIVE

To investigate bacterial nasopharyngitis as a cause of adult upper respiratory infection.

DESIGN

Prospective case series.

SETTING

Walk-in medical clinic of a university hospital.

PATIENTS

507 patients with cold or flu symptoms, sore throat, or recent cough; 21 control subjects without symptoms of upper respiratory infection.

MEASUREMENTS AND MAIN RESULTS

After thorough history and physical examination, the patients underwent nasopharyngeal aspiration and throat culture. Nasopharyngeal specimens were cultured for both bacteria and viruses; antigens for influenza, parainfluenza, and respiratory syncytial virus were sought by enzyme-linked immunosorbent assay (ELISA); serum antibodies to viral respiratory pathogens were determined. Group A beta-hemolytic streptococci grew from the throat specimens of 39 of the 507 patients (8%) or 38 of 334 patients (11%) who had clinical diagnoses of pharyngitis. Thirty-three cases of influenza A, 20 cases of influenza B, and seven cases of parainfluenza infections were diagnosed. Bacteria were cultured from the nasopharyngeal secretions of 284 patients (56%). In contrast to pharyngeal culture, commensal mixed flora were rarely found in nasopharyngeal culture. Nasopharyngeal culture of bacteria usually considered to be respiratory pathogens was significantly associated with the presence of leukocytes. Streptococcus pneumoniae (odds ratio 6.0, 95% confidence interval 2.6-14.2), Moraxella catarrhalis (odds ratio 12.9, 95% confidence interval 3.1-79.5), and Hemophilus influenzae (odds ratio 3.0, 95% confidence interval 1.2-7.4) were all associated with the presence of leukocytes. In contrast, nasopharyngeal culture of coagulase-negative staphylococci, mixed flora, and the documentation of a viral infection were not associated with the presence of leukocytes. For none of 21 control subjects were "pathogenic" bacteria found.

CONCLUSIONS

These data suggest that potentially pathogenic bacteria may have a causal role in adult nasopharyngitis, although further data are needed to confirm this hypothesis.

Quantitative bacterial culture from adenoid lymphatic tissue with special reference to Haemophilus [corrected]

Homogenized adenoid tissue from 55 children (28-153 months) undergoing adenoidectomy because of nasopharyngeal obstruction was investigated by means of quantitative aerobic bacterial culture. The children were divided into two groups, the hypertrophy alone group--AH (n = 29)--and the hypertrophy with longstanding secretory otitis media group--SOM (n = 26). A nasopharyngeal culture was obtained preoperatively from 38 of the cases. Non-typeable H. influenzae (NTHI) was found in twice as many cases in the AH group as in the SOM group, 21/29 (72%) compared to 11/26 (42%) (p < 0.05) and in a significantly higher mean concentrations, 5.7 x 10(5) CFU/g compared to 1.9 x 10(5) CFU/g (p = 0.02). For the other aerobic potentially pathogenic bacteria no such difference was found. The bulk of the NTHI-positive cases and the cases with the highest concentrations were found in the children below the age of 6 years. In the nasopharyngeal cultures NTHI alone or together with S. pneumoniae and/or B. catarrhalis was found in 29% of the cases in both the AH group and SOM group. NTHI was found in only 50% of the nasopharyngeal cultures corresponding to a positive quantitative culture (10/20). These findings suggest that NTHI is harboured within the adenoid and could thereby chronically stimulate the local immune defense. However, the present study indicates that there is no aerobic bacterial overload in the adenoid tissue in children with SOM compared to children without middle-ear disease.

Nasopharyngeal bacterial flora in otitis prone children treated with immunoglobulin

The present study was undertaken to evaluate possible beneficial effects of regularly given, long term immunoglobulin prophylaxis of children below 2 years of age with recurrent acute otitis media (RAOM). The nasopharyngeal bacterial flora and the frequency of acute otitis media (AOM) and secretory otitis media SOM were studied. Every second of 44 children with 3 or more periods of AOM during the last year received immunoglobulin intramuscularly (Gammaglobulin Kabi 165 mg/l, 0.45 ml/kg b.w.) every third week for 6 months, while the other 22 children served as controls. All children were followed for 12 months. Immunoglobulin prophylaxis neither influenced the nasopharyngeal flora, nor the frequency of AOM or SOM periods. Children with AOM or SOM more often harbored bacterial pathogens in their nasopharynx than children with normal middle ear status. Also, the immunoglobulin prophylaxis did not influence the increased frequency of bacterial pathogens in the nasopharynx of children attending public day care or family day care as compared to those taken care of at home.

Nasopharyngeal colonization by nontypeable Hemophilus influenzae in children: the effect of serum bactericidal antibody

The effect of serum bactericidal antibody on colonization with NTHI was studied in 26 children. Serum bactericidal antibody did not prevent colonization with NTHI in the nasopharynx. Antibody was detected in 53% before, 91% during, and 100% after documented colonization. The log titer of antibody was significantly higher during (1.18 +/- 0.56), p less than 0.002; and after (1.31 +/- 0.29), p greater than 0.001 compared to before colonization (0.49 +/- 0.51). The roles of secretory IgA and normal nasopharyngeal flora in inhibiting pathogenic bacteria are discussed.

Nasopharyngeal flora in the first three years of life in normal and otitis-prone children

Nasopharyngeal carriage of the three major middle ear pathogens (Streptococcus pneumoniae, nontypeable Hemophilus influenzae, and Moraxella catarrhalis) was evaluated prospectively in a group of 110 children followed up for the first 3 years of life. The findings suggested that nasopharyngeal carriage of middle ear pathogens increases significantly during respiratory illness among the general population of young children; however, otitis-prone children demonstrated a tendency to carry nontypeable H influenzae at an unusually high rate even during health. This propensity to carry nontypeable H influenzae might explain why nontypeable H influenzae is a major cause of recurrent or chronic otitis media.

Treatment failure in otitis-prone children with prophylactic tympanostomy tubes is correlated with nasopharyngeal Haemophilus influenzae colonization

Tympanostomy tubes are used to prevent recurrent otitis media among otitis-prone children. However, not all children benefit from this treatment. In the present study 28 children (19 boys, 9 girls) were given bilateral tympanostomy tubes at age 9-22 months (mean 14 months). They were observed 6 months before and after tube insertion. The treatment was considered successful for 20 children. Among these, 16 completely lacked or had one episode of middle ear discharge and 4 had otorrhea on two occasions. A total of 8 children suffered from three or more episodes of otorrhea and were considered as treatment failures. In the failure group, the nasopharyngeal average carrier rate of H. influenzae 6 months before and after tube insertion was 64% vs. 29% in the group responding well to the treatment (p less than 0.001). Nonencapsulated forms of H. influenzae were in a great majority. In the failure group 7 out of 8 presented middle ear discharge as soon as within 2 weeks after tube insertion whereas this occurred in only 3 out of 20 in the responding group. IgG, IgG1 and IgG2 antibody response to pneumococcal polysaccharide (6A, 19F) were equally distributed in the two groups. The present data suggest that one reason for an unsatisfactory response to treatment with prophylactic tympanostomy tubes is nasopharyngeal colonization and subsequent middle ear infections caused by H. influenzae.

Occurrence of middle ear pathogens in the nasopharynx of young individuals. A quantitative study in four age groups

Colonization of middle ear pathogens (S. pneumoniae, H. influenzae and B. catarrhalis), potential pathogens (S. aureus and coagulase-negative staphylococci) and non-pathogens was determined quantitatively on the posterior wall of the nasopharynx (NPH) of children (four age groups: under 2 years, 2-5 years, 6-10 years and 11-15 years). None of the 90 individuals examined was suffering at the time of bacterial sampling from acute otitis media (AOM), sinusitis, or tonsillitis. All individuals under 2 years of age harboured middle ear pathogens in the NPH, but only 40% of the individuals of the oldest age group (p less than 0.001). Furthermore, in the youngest group, 57% of the cases had pathogens in the NPH, which completely dominated the bacterial flora, i.e. constituted more than 90% of the total bacterial count when calculated as CFU/cm2. The corresponding count in the oldest age group was only 20% (p less than 0.01). One important reason for the high incidence of AOM among young children in particular seems to be the noticeable accumulation of middle ear pathogens in huge quantities in the NPH in this age group.

The bacterial flora of the nasopharynx, with special reference to middle ear pathogens. A quantitative study in twenty children

Quantification of middle ear pathogens (S. pneumoniae, H. influenzae and B. catarrhalis) and potential pathogens (S. aureus and coagulase-negative staphylococci) adhering to the posterior wall of the nasopharynx was performed in 20 patients of whom 5 were suffering from secretory otitis media (SOM), 5 from recurrent attacks of acute otitis media (rAOM), 5 from attacks of upper respiratory infection (URI) and 5 from blocked nose (BN). While the patients were under general anesthesia a glass cylinder (diameter 1.3 cm) was pressed against the posterior wall of the nasopharynx and swabs were taken from the mucosa delineated by the glass tube. Quantification of the bacteria was performed using blood and chocolate agar plates. Total bacterial counts ranged between 2.6 x 10(4)CFU/cm2 and 4.0 x 10(8)CFU/cm2. In the rAOM group, 4 out of 5 children had bacterial counts in the nasopharynx which constituted of 95% pathogens. Coagulase-negative staphylococci never exceeded 1.9 x 10(5)CFU/cm2.

Colonization of middle ear pathogens in the nasopharyngeal opening of the Eustachian tube during secretory otitis media

Colonization of middle ear pathogens (S. pneumoniae, H. influenzae and B. catarrhalis) in the nasopharyngeal opening of the Eustachian tube (NO) was charted in 94 patients (170 ears) suffering from secretory otitis media (SOM). Subsequent determination of microorganisms in the middle ear effusion was performed. 76% of the patients had colonization of pathogens in the NO, while pathogens colonized the middle ear cavity (MEC) in 30% of the cases. Predominant pathogen was S. pneumoniae, followed by B. catarrhalis and H. influenzae. When colonizing the MEC, there was a 100% correlation to NO regarding B. catarrhalis, 81% correlation for S. pneumoniae and 57% for H. influenzae. S. aureus and/or coagulase-negative staphylococci were only occasionally found in the NO. Accumulation of a sticky glue effusion material in the middle ear cavity may serve as a barrier against ascending pathogens from the nasopharynx.

Nasopharyngeal bacteriology and secretory otitis media in young children

A prevalence study was performed on the nasopharyngeal bacteriology of 112 young children, aged 4-6 years. During the preceding 2 years, 74 of these children had suffered from secretory otitis media (SOM) and 40 had had normal middle ear ventilation. At the examination, one-third of the children with SOM had improved their middle ear status (previous SOM group), whereas otomicroscopy and tympanometry remained unchanged in the healthy group. The nasopharyngeal swab sample was obtained from behind the soft palate by the oral route. The isolation rate of Streptococcus pneumoniae was significantly higher in the SOM group than in the two other groups of children (p less than 0.006). The most commonly isolated capsular types of pneumococci were 6, 19, and 23, corresponding to the types involved in acute otitis media. The isolation rate of Haemophilus influenzae was 50% and an even distribution was found among the three groups of children examined. Biotypes I, II, III and IV accounted for 75% of the isolated cases of H. influenzae. As in acute otitis media, S. pneumoniae also seemed to play an important role in the pathogenesis of tubal dysfunction and SOM, and the difference is probably caused by variations in the quantitative colonization of pneumococci in the nasopharynx.

Relapse of acute purulent otitis media: antibiotic sensitivities of nasopharyngeal pathogens

The present investigation was conducted to find out if a relapse of acute purulent otitis media is associated with a decreased sensitivity of nasopharyngeal pathogens to commonly used antimicrobial agents. All but one of 63 children with relapse included in this study yielded one or more of the classical middle ear pathogens (Streptococcus pneumoniae, Haemophilus influenzae, Branhamella catarrhalis, S. pyogenes) in their nasopharynx (NPH) secretions. S. pneumoniae was the predominating isolate from NPH (71% of the patients) as well as from middle ear effusion (53%). At a control visit 4 weeks after the start of antibiotic therapy, 91% were NPH carriers of potential pathogens and S. pneumoniae was still the most common isolate (53%). Beta-lactamase was produced by 55% of B. catarrhalis isolates from the NPH specimens on the first visit, but only by 33% of B. catarrhalis isolates on the control visit. Two NPH isolates of H. influenzae produced beta-lactamase. One isolate of S. pneumoniae (serotype 18) was intermediately sensitive to phenoxymethylpenicillin. Generally low MICs were found for erythromycin and cefaclor. H. influenzae isolates were generally sensitive to ampicillin in vitro, but only 1 isolate was fully sensitive to erythromycin. B. catarrhalis isolates were uniformly sensitive to doxycycline and trimethoprim/sulphamethoxazole. No tolerance to penicillin was demonstrated in S. pneumoniae and H. influenzae. The present data indicate that the relapse of acute otitis media is not associated with development of tolerance or resistance to therapeutic antimicrobials commonly used.

Combined IgG2, IgG4 and IgA deficiency: low C1q concentrations and the presence of excess C1r and C1s in an adult patient with recurrent pneumococcal infections

The complement (C) profile was investigated in an adult patient with combined IgG2, IgG4 and IgA deficiency and recurrent pneumococcal infections. The analysis revealed no gross impairment of the classic and alternative pathways of C activation. However, the concentrations of circulating C1q were persistently decreased, and the sera contained an excess of C1r-C1s complexes, resembling the C1 aberrations previously found in children with recurrent acute otitis media. The concentrations of C4 in the patient were persistently low. This could be ascribed to partial C4 deficiency with lack of C4A variants. The patient's IgG and IgM antibody responses to pneumococcal capsular polysaccharides and to other bacterial carbohydrate antigens were very poor. Interestingly, pneumococcal C-polysaccharide (CPS) could be detected in serum obtained during infection-free periods. Since CPS has been shown to bind C1q without causing C1 activation, the possibility was considered that the C1 aberrations in serum were due to circulating CPS. After administration of intramuscular gammaglobulin to the patient, the serum C1q levels were observed to return to normal.

A prospective study demonstrating an association between plasma IgG2 concentrations and susceptibility to otitis media in children

Plasma IgG subclass levels of 20 children, 12 and 32 months of age, who were susceptible to acute purulent otitis media, were compared with those of 20 age-matched control children. The IgG2 levels were significantly lower in the otitis-prone group, with a mean of 0.58 +/- 0.30 g/l at 12 months of age (controls 0.85 +/- 0.39) and 0.82 +/- 0.30 at 32 months of age (controls 1.38 +/- 0.49). Otitis-prone children with IgG2 levels less than or equal to 0.58 g/l (at 12 months of age) were found to suffer from Haemophilus influenzae infections 2.6 times as often as those with IgG2 levels greater than 0.58 g/l. On the other hand pneumococci were found 1.9 times as often in the group with IgG2 level greater than 0.58 g/l, as in the group with IgG2 level less than or equal to 0.58 g/l. Otitis proneness seems partly to be due to an immunological incompetence of IgG2, which also influences the bacterial spectrum of the infections.

Relative proportions of Haemophilus species in the throat of healthy children and adults

To determine normal proportions of pharyngeal Haemophilus species, qualitative and quantitative mapping of the species in the pharynx of ten healthy children and ten healthy adults was carried out using a selective and a non-selective medium. Haemophilus organisms were present in all samples, comprising approximately 10% of the total cultivable flora (range 0.6-36.9%). Haemophilus parainfluenzae was a member of the normal flora throughout life, constituting 74% of pharyngeal Haemophilus organisms. Haemophilus segnis and Haemophilus paraphrophilus occurred more frequently in samples from adults, whereas Haemophilus haemolyticus was present in only one sample. Non-encapsulated Haemophilus influenzae strains, usually of multiple biotypes, were present in 80% of the children but accounted for a mean of only 1.8% of the total flora. Their number decreased with increasing age; 40% of the adults harbored Haemophilus influenzae but only of a single biotype which constituted a minor proportion of the total flora (mean 0.15%). These findings suggest that host mechanisms can influence changes in the proportions of Haemophilus influenzae strains colonizing the host.