Quantitative cultures of middle-ear fluid in acute otitis media

Rapid typing of Moraxella catarrhalis subpopulations based on outer membrane proteins using mass spectrometry

Moraxella catarrhalis is a major mucosal pathogen of the human respiratory tract both in children and in adults. Two subpopulations of this organism have been described that differ in 16S rRNA gene sequence and virulence traits. Three 16S rRNA types have been defined. 2-DE followed by protein identification by MS revealed significant differences in the outer membrane protein (OMP) patterns of each M. catarrhalis 16S rRNA type. Approximately 130 features were detected on the 2-DE map of each M. catarrhalis 16S rRNA type. However, only 50 features were expressed by all strains. Furthermore, direct profiling of isolated OMP using MALDI-TOF MS resulted in a characteristic spectral fingerprint for each 16S rRNA type. Fingerprints remained identical when intact cells instead of isolated OMP were analyzed. This finding suggests that the source of desorbed ions is the outer membrane. Based on the fingerprint we were able to assign 18 well-characterized clinical M. catarrhalis isolates to the correct subpopulation. Therefore, MALDI-TOF of intact M. catarrhalis provides a rapid and robust tool for M. catarrhalis strain typing that could be applied in epidemiological studies.

Moraxella catarrhalis strains with reduced expression of the UspA outer membrane proteins belong to a distinct subpopulation

The outer membrane proteins UspA1 and UspA2 are candidate antigens for a Moraxella catarrhalis vaccine. We previously reported that 103 of 108 isolates (95%) from young children expressed UspA1 detected by reactivity with the monoclonal antibody mAb24B5. The aim of the present study was to investigate mechanisms controlling UspA1 expression by analysis of five mAb24B5 non-reactive isolates. Four of these strains were characterized by (i) decreased or absent transcription of uspA1 and uspA2 and (ii) clustered mutations and deletions in the promoter region of both uspA1 and uspA2. Antigenic or phase variation were not responsible for reduced levels of UspA1 expression. While mAb24B5-positive isolates expressing normal levels of uspA1 and uspA2 mRNA belonged to the previously described 16S rRNA type 1 phylogenetic group, these four mAb24B5-negative isolates were found to belong to the 16S rRNA gene types 2 or 3. The remaining mAb24B5-negative isolate (#610) belonged to 16S rRNA type 1 and exhibited a posttranscriptional defect of UspA1 expression defined by normal levels of uspA1 mRNA and both recombinant and in vitro expression of mAb24B5-reactive UspA1. In conclusion, M. catarrhalis clinical isolates exhibiting reduced expression of UspA1 and UspA2 belonged to a distinct phylogenetic subpopulation. A UspA-based vaccine is unlikely to be effective against such isolates.

Mucosal immune response to specific outer membrane proteins of Moraxella catarrhalis in young children

BACKGROUND

Moraxella catarrhalis is an important cause of otitis media. A number of candidate antigens for a future infant otitis media vaccine have been identified, but their mucosal immunogenicity induced by nasopharyngeal M. catarrhalis colonization has not been characterized. The aim of this study was to determine the salivary IgA response to M. catarrhalis outer membrane proteins (OMP) in young children.

METHODS

Children ages 1 to 24 months evaluated for acute respiratory tract infection were prospectively enrolled. M. catarrhalis nasopharyngeal colonization was determined by (1) selective culture and (2) detection by reverse transcription-PCR of messenger RNA specific for the OMP UspA1 and UspA2. Salivary IgA responses were detected by immunoblot analysis of M. catarrhalis OMP. Isogenic knockout mutants for UspA1, UspA2, hemagglutinin (Hag), transferrin-binding protein B (TbpB) and CopB were constructed for identification of specific target OMP.

RESULTS

Sixty-six patients were studied. The rates of M. catarrhalis colonization by culture, reverse transcription-PCR for messenger RNA and mRNA were 40, 94 and 58%, respectively. Anti-M. catarrhalis salivary IgA was detected in 62 patients (94%). IgA directed against a >250-kDa antigen (assigned to UspA1/UspA2 by mutant analysis) and a 200-kDa antigen (Hag) were detected in 65 and 70% of patients, respectively. Bands at 80 to 85 kDa (82%) consisted of IgA directed against monomeric UspA2, TbpB and CopB.

CONCLUSIONS

colonization occurring in early infancy is associated with a consistent mucosal immune response directed against the UspA proteins, Hag and other OMP. The data suggest that several M. catarrhalis OMP are immunogens of the nasopharyngeal mucosal immune system of infants.

A protective epitope of Moraxella catarrhalis is encoded by two different genes

The high-molecular-weight UspA protein of Moraxella catarrhalis has been described as being both present on the surface of all M. catarrhalis disease isolates examined to date and a target for a monoclonal antibody (MAb 17C7) which enhanced pulmonary clearance of this organism in a mouse model system (M. E. Helminen et al., J. Infect. Dis. 170:867-872, 1994). A recombinant bacteriophage that formed plaques which bound MAb 17C7 was shown to contain a M. catarrhalis gene, designated uspA1, that encoded a protein with a calculated molecular weight of 88,271. Characterization of an isogenic uspA1 mutant revealed that elimination of expression of UspA1 did not eliminate the reactivity of M. catarrhalis with MAb 17C7. In addition, N-terminal amino acid analysis of internal peptides derived from native UspA protein and Southern blot analysis of M. catarrhalis chromosomal DNA suggested the existence of a second UspA-like protein. A combination of epitope mapping and ligation-based PCR methods identified a second M. catarrhalis gene, designated uspA2, which also encoded the MAb 17C7-reactive epitope. The UspA2 protein had a calculated molecular weight of 62,483. Both the isogenic uspA1 mutant and an isogenic uspA2 mutant possessed the ability to express a very-high-molecular-weight antigen that bound MAb 17C7. Southern blot analysis indicated that disease isolates of M. catarrhalis likely possess both uspA1 and uspA2 genes. Both UspA1 and UspA2 most closely resembled adhesins produced by other bacterial pathogens.

Rationale behind high-dose amoxicillin therapy for acute otitis media due to penicillin-nonsusceptible pneumococci: support from in vitro pharmacodynamic studies

To evaluate whether increased doses of amoxicillin should be used to treat acute pneumococcal otitis media, an in vitro pharmacokinetic model was used to evaluate the killing of pneumococci by amoxicillin when middle ear pharmacokinetics were simulated. Logarithmic-phase cultures were exposed to peak concentrations of 3, 6, and 9 microg of amoxicillin per ml every 12 h, and an elimination half-life of 1.6 h was simulated. Changes in viable bacterial counts were measured over 36 h. All three doses rapidly decreased the viable bacterial counts of penicillin-susceptible strains below the 10-CFU/ml limit of detection by 6 to 10 h and maintained counts below this limit through 36 h. The 3-microg/ml peak dose was much less effective against two of three strains with intermediate penicillin resistance and all three penicillin-resistant strains, with bacterial counts approaching those in drug-free control cultures by 12 h. The 6-microg/ml peak dose completely eliminated two of three strains with intermediate penicillin resistance and maintained viable counts of the other nonsusceptible strains at 1.5 to 2 logs below the initial inoculum through 36 h. The 9-microg/ml peak dose was most effective, completely eliminating all three strains with intermediate penicillin resistance and maintaining the viable counts of the resistant strains at 3 to 4 logs below the original inoculum. The pharmacodynamics observed in this study suggest that peak concentrations of amoxicillin of 6 to 9 microg/ml may be sufficient for the elimination of penicillin-nonsusceptible pneumococcal strains causing otitis media, especially those with intermediate resistance to amoxicillin. In vivo pharmacokinetic studies are needed to determine if these levels can be achieved in middle ear fluid with amoxicillin at 70 to 90 mg/kg/day divided into two daily doses. If these levels are reliably achieved, then clinical studies are warranted.

Moraxella (Branhamella) catarrhalis bacteremia in children. A report of two patients and review of the literature

We report two cases of Moraxella catarrhalis (M. catarrhalis) bacteremia in apparently healthy children. One patient had bilateral otitis media and the other had pharyngitis and sinusitis; both patients had uncomplicated clinical courses. A literature review revealed 22 reported cases of M. catarrhalis bacteremia in children, 14 (63%) of which occurred in patients who had no identified underlying condition. Eight (36%) cases were seen in children who were immunocompromised. Nine (40%) patients presented with either purpura, petechia, or a maculopapular rash. M. catarrhalis is well known as a respiratory pathogen, but it has not been recognized as a common cause of unsuspected bacteremia in children.

A major outer membrane protein of Moraxella catarrhalis is a target for antibodies that enhance pulmonary clearance of the pathogen in an animal model

A murine immunoglobulin G monoclonal antibody (MAb) raised against outer membrane vesicles of Moraxella catarrhalis 035E was shown to bind to a surface-exposed epitope of a major outer membrane protein of this organism. This outer membrane protein, which had an apparent molecular weight of approximately 80,000 in sodium dodecyl sulfate-polyacrylamide gels, was designated CopB. MAb 10F3, reactive with CopB, bound to a majority (70%) of M. catarrhalis strains tested. More importantly, mice passively immunized with MAb 10F3 exhibited an enhanced ability to clear a bolus challenge of M. catarrhalis from their lungs, a result which suggested that CopB might have potential as a vaccine candidate. The M. catarrhalis gene encoding CopB was cloned in Escherichia coli, and nucleotide sequence analysis of the copB gene indicated that the CopB protein was synthesized with a leader peptide, a finding confirmed by N-terminal amino acid sequence analysis of the mature CopB protein purified from M. catarrhalis 035E. Southern blot analysis showed that chromosomal DNA from seven different M. catarrhalis strains hybridized with a probe comprising the majority of the copB structural gene from strain 035E. Additional data emphasizing the extent of conservation of the CopB protein among M. catarrhalis strains were obtained from Western immunoblot analyses with polyclonal antisera raised against CopB proteins from different M. catarrhalis strains used to probe the recombinant form of the CopB protein from strain 035E. The ability of the CopB protein to function as a target for biologically active antibodies and its apparent conservation among M. catarrhalis strains warrant further investigation of this outer membrane protein as a potential vaccine candidate.

An in vitro pharmacodynamic model to simulate antibiotic behavior of acute otitis media with effusion

The purpose of this investigation was to develop an in vitro pharmacodynamic model (IVPM) that would simultaneously simulate in vivo serum and middle ear amoxicillin pharmacokinetic characteristics of acute (purulent) otitis media and then utilize the IVPM to assess amoxicillin-mediated killing of a type 7F Streptococcus pneumoniae (MIC = 0.002 mg/L). The IVPM consisted of a sterile central compartment and a membrane-bound "infected" peripheral compartment. Peak peripheral compartment amoxicillin concentrations occurred within 2 hr after its introduction into the central compartment and were approximately 30% of peak central compartment concentrations. Amoxicillin elimination from the central compartment was designed to provide a 1-hr t 1/2. Amoxicillin elimination from the peripheral compartment was slower than from the central compartment, with an average half-life of 2.3 hr. Significant concentration-related differences in maximal bacterial kill rates were not detected over the range of amoxicillin concentrations studied (0.26 to 14.6 mg/L). However, at peak central compartment amoxicillin concentrations of less than or equal to 2 mg/L, a lag phase in killing was observed. In general, the in vitro pharmacokinetic data derived from this model compare well with published in vivo data.

Effect of prior antibiotic treatment on middle ear disease in children

The effect of prior antibiotic treatment on the course of otitis media was assessed in a group of 62 children who experienced 83 episodes of ear infection during 3 years of observation. Bacterial quantitation in middle ear fluids demonstrated a significantly higher colony count in symptomatic children (3.9 x 10(4) +/- 12 bacteria per milliliter) compared to asymptomatic children (6.3 x 10(3) +/- 10 bacteria per milliliter; p = .05). Bacterial counts similarly tended to be higher in children with Streptococcus pneumoniae (4.0 x 10(6) +/- 16 bacteria per milliliter) and Hemophilus influenzae (2.0 x 10(6) +/- 16 bacteria per milliliter), who were more often symptomatic (73% and 55%, respectively, versus 38%) than children with Moraxella catarrhalis (7.9 x 10(3) +/- 2). Antibiotic therapy between 3 and 30 days prior to bacterial diagnosis was associated with a reduction in symptoms from 70% to 38% (p less than .025). However, prior treatment did not statistically reduce bacterial colony counts, although S pneumoniae decreased 90% in the previously treated group. Resistance to ampicillin occurred in 0% of S pneumoniae, 39% of nontypeable H influenzae, and 80% of M catarrhalis subjects without prior treatment and in 0%, 46%, and 100%, respectively, of subjects previously treated (p less than .025). These data suggest that prior treatment has a significant impact on the subsequent course of otitis media in children.

Antimicrobial treatment of acute otitis media

No single antimicrobial drug is best suited for all patients with AOM. Amoxicillin and TMP-SMZ, however, remain first-line drugs in the initial treatment of uncomplicated AOM in the non-neonate. In other situations the drug selected depends on the patient's age, associated illnesses, recent history of otitis media, and drug hypersensitivity. Pharmacokinetic studies of AOM treatment are essential in generating more precise recommendations for antimicrobial drug use.

Chlamydia trachomatis in the etiology of acute otitis media

In an effort to show that Chlamydia trachomatis (CT) may be involved in the causation of acute otitis media (AOM), we performed three experiments. In the first, we inoculated the tympanic bullae of 6 chinchillas with CT. Five of the 6 inoculated animals developed CT AOM. In the second experiment, we sprayed the nasopharynx of 10 chinchillas with CT. Of these, 8 developed both pharyngitis and AOM, and in 6, live CT was cultured from the middle ear and pharynx. In the third experiment, 5 chinchillas had their conjunctiva inoculated with CT. Three developed CT conjunctivitis. Of these, 2 developed CT pharyngitis and 1 developed CT AOM. We concluded that CT will cause AOM in the chinchilla by direct inoculation into the middle ear as well as indirectly by infection of the nasopharynx and conjunctiva.

Branhamella catarrhalis: an organism gaining respect as a pathogen

Branhamella catarrhalis was formerly regarded as a common, essentially harmless inhabitant of the pharynx. This misapprehension was caused, in part, by confusion with another pharyngeal resident, Neisseria cinerea. The two organisms can now be differentiated by the positive reactions of B. catarrhalis in tests for nitrate reduction and hydrolysis of tributyrin and DNase. B. catarrhalis is currently recognized as the third most frequent cause of acute otitis media and acute sinusitis in young children. It often causes acute exacerbations of chronic bronchopulmonary disease in older or immunocompromised adults and is incriminated occasionally in meningitis, endocarditis, bacteremia, conjunctivitis, keratitis, and urogenital infections. Virulence-associated factors, such as pili, capsules, outer membrane vesicles, iron acquisition proteins, histamine-synthesizing ability, resistance to the bactericidal action of normal human serum, and binding to the C1q complement component, have been identified in some strains. beta-Lactamase producing strains, first detected in 1976, have risen to approximately 75% worldwide. Thus far, however, practically all American strains of B. catarrhalis remain susceptible to alternative antibiotics. A possible selective advantage of recent isolates is their reportedly heightened tendency for adherence to oropharyngeal cells from patients with chronic bronchopulmonary disease.

Reappearance of group A streptococci in acute otitis media

Specimens from acute otitis media (AOM) examined in the first quarter of the years 1986, 1987, 1988, and 1989 were reviewed in order to point out any changes in the bacteriological etiology. A total of 1,722 specimens were taken in the community and in the hospitals of a county of 500,000 inhabitants in the 4-year-period: 447 (1986), 420 (1987), 388 (1988), 467 (1988). The majority of the specimens came from children less than 10 years of age. The specimen sampling technique differed between the various otologists, but their sampling techniques were constant through the years. Haemophilus influenzae was the most frequent isolate and held a constant incidence of 29.9% with little variation. In 1986-88 Streptococcus pneumoniae was the second (19.8%) and group A streptococci (GAS) the third (9.8%) most common agent in frequency. In 1989 a change in the etiologic agents was seen as GAS increased in frequency to 18.8% (p less than 0.001), while no significant changes occurred in the frequency of H. influenzae and S. pneumoniae. 33% of the specimens were negative in the whole period. It is too early to decide whether a transient epidemic has occurred or whether the findings announce a more constant change in etiology.

Determination of the epidemiology and transmission of nontypable Haemophilus influenzae in children with otitis media by comparison of total genomic DNA restriction fingerprints

It is assumed that the causative bacteria in children suffering from otitis media reach the middle ear via the eustachian tube. The purpose of this investigation was to use endonuclease restriction of bacterial chromosomal DNA to compare isolates of nontypable (NT) Haemophilus influenzae obtained from the nasopharynx and from middle ear (ME) effusions of patients with otitis media. Strains of NT H. influenzae were isolated from the nasopharynx (NP) and affected ME from a group of 13 unrelated children with otitis media with effusion (OME). For 12 of these children, identical strains were isolated from the NP and ME in a first episode of OME. Each of these 12 sets differed from the other 11. Six of these children suffered from a second episode of OME with NT H. influenzae. Five of these children with recurrence again had identical NP and ME strains. These results suggest that at the time of an episode of OME, there is one predominant strain of NT H. influenzae that colonizes both the NP and ME. The strains of NT H. influenzae isolated from all six of the second episodes were different from strains from the first episode, indicating turnover of the predominant strain in the NT H. influenzae population between episodes. When we investigated three siblings with concurrent episodes of OME, we found that they shared several similar strains of NT H. influenzae, thereby demonstrating that within a family, transmission of NT H. influenzae from child to child is possible. These results from DNA fingerprinting were essentially identical when compared with results from outer membrane protein subtyping performed on the same set of strains. The analysis of endonuclease restriction patterns of total genomic DNA provides a sensitive measure of genetic dissimilarity between strains and represents an easily applicable method for epidemiological and transmission studies of bacterial infections associated with NT H. influenzae.

Longitudinal studies of experimental otitis media with Haemophilus influenzae in the gerbil

Haemophilus influenzae non-typable strain 119 was found to cause severe otitis media with sequellae when inoculated into the middle ear cavities of the Mongolian gerbil, Meriones unguiculatus. Acute inflammation was followed by the development of highly vascular granulation tissue and formation of new bone within the middle ear bulla. These changes persisted throughout the 14-week study in the untreated animals. The gerbil was variably susceptible to otitis media caused by inoculating 30-3000 bacterial cells and 100% susceptible to greater than 3000 cells. The susceptibility of the gerbil to common etiological agents of otitis media allows its use as an appropriate model of the disease.

A randomized controlled trial of cefaclor compared with trimethoprim-sulfamethoxazole for treatment of acute otitis media

We performed a randomized controlled trial of cefaclor administered twice daily compared with trimethoprim-sulfamethoxazole (TMP-SMZ) administered twice daily for the treatment of acute otitis media. Pathogens were eradicated from the middle ear exudate after 3 to 6 days of therapy in 35 of 37 (95%) patients given TMP-SMZ compared with 28 of 40 (70%) given cefaclor (P = 0.017). Haemophilus influenzae was eliminated in 13 of 14 (93%) patients given TMP-SMZ compared with 10 of 18 (56%) given cefaclor (P = 0.047). Clinical outcomes failed to distinguish between patients given TMP-SMZ or cefaclor. Symptoms improved despite persistent infection in 11 of 13 (85%) patients; middle-ear effusion persisted after therapy in 38 of 61 (62%) patients despite eradication of pathogens. We conclude that twice daily TMP-SMZ is more efficacious than twice daily cefaclor for the treatment of acute otitis media and that clinical outcomes may fail to detect differences between antibacterial agents in comparative drug trials in acute otitis media.