Comparison of Moraxella catarrhalis isolates from children and adults for growth on modified New York City medium and potential virulence factors

Antimicrobial susceptibility and impact of macrolide antibiotics on Moraxella catarrhalis in the upper and lower airways of children with chronic endobronchial suppuration

INTRODUCTION

Moraxella catarrhalis is an important but insufficiently studied respiratory pathogen.

AIM

To determine antibiotic susceptibility and impact of recent antibiotics on M. catarrhalis from children with chronic endobronchial suppuration.

METHODOLOGY

We cultured nasopharyngeal (NP) swabs and bronchoalveolar lavage (BAL) fluids collected from children who were prospectively enrolled in studies of chronic cough and had flexible bronchoscopy performed. Recent β-lactam or macrolide antibiotic use was recorded. M. catarrhalis isolates stored at -80 °C were re-cultured and susceptibility determined to a range of antibiotics including the macrolide antibiotic erythromycin.

RESULTS

Data from concurrently collected NP and BAL specimens were available from 547 children (median age 2.4 years) enrolled from 2007 to 2016. M. catarrhalis NP carriage was detected in 149 (27  %) children and lower airway infection (≥10⁴ c.f.u. ml^-1 BAL) in 67 (12  %) children. In total, 91  % of 222 M. catarrhalis isolates were β-lactamase producers, and non-susceptibility was high to benzylpenicillin (98 %), cefaclor (39 %) and cotrimoxazole (38 %). Overall, >97  % isolates were susceptible to cefuroxime, chloramphenicol, erythromycin and tetracycline; three isolates were erythromycin-resistant (MIC >0.5 mg l^-1). Recent macrolide antibiotics (n=152 children, 28 %) were associated with significantly reduced M. catarrhalis carriage and lower airway infection episodes compared to children who did not receive macrolides; odds ratios 0.19 (95  % CI 0.10-0.35) and 0.15 (0.04-0.41), respectively.

CONCLUSION

Despite the frequent use of macrolides, few macrolide-resistant isolates were detected. This suggests a fitness cost associated with macrolide resistance in M. catarrhalis. Macrolide antibiotics remain an effective choice for treating M. catarrhalis lower airway infection in children with chronic endobronchial suppuration.

Virulence determinants of Moraxella catarrhalis: distribution and considerations for vaccine development

Moraxella catarrhalis is a human-restricted opportunistic bacterial pathogen of the respiratory mucosa. It frequently colonizes the nasopharynx asymptomatically, but is also an important causative agent of otitis media (OM) in children, and plays a significant role in acute exacerbations of chronic obstructive pulmonary disease (COPD) in adults. As the current treatment options for M. catarrhalis infection in OM and exacerbations of COPD are often ineffective, the development of an efficacious vaccine is warranted. However, no vaccine candidates for M. catarrhalis have progressed to clinical trials, and information regarding the distribution of M. catarrhalis virulence factors and vaccine candidates is inconsistent in the literature. It is largely unknown if virulence is associated with particular strains or subpopulations of M. catarrhalis, or if differences in clinical manifestation can be attributed to the heterogeneous expression of specific M. catarrhalis virulence factors in the circulating population. Further investigation of the distribution of M. catarrhalis virulence factors in the context of carriage and disease is required so that vaccine development may be targeted at relevant antigens that are conserved among disease-causing strains. The challenge of determining which of the proposed M. catarrhalis virulence factors are relevant to human disease is amplified by the lack of a standardized M. catarrhalis typing system to facilitate direct comparisons of worldwide isolates. Here we summarize and evaluate proposed relationships between M. catarrhalis subpopulations and specific virulence factors in the context of colonization and disease, as well as the current methods used to infer these associations.

In vitro inflammatory responses elicited by isolates of Alloiococcus otitidis obtained from children with otitis media with effusion

Alloiococcus otitidis is usually detected in children with otitis media (OM) by PCR as it is not often detected by routine culture. Our improved method for its isolation obtained A. otitidis from nearly 50% of 78 children with OM with effusion. The role of A. otitidis in pathogenesis of OM is unclear. This study tested two hypothesis: (1) that fresh isolates of A. otitidis would elicit pro-inflammatory cytokines from THP-1 monocytic cells equivalent to those induced by Streptococcus pneumoniae; (2) priming THP-1 cells with interferon-gamma (IFN-γ) a surrogate for virus infection, would enhance pro-inflammatory responses. Recent clinical isolates of A. otitidis, S. pneumoniae (ATCC 49619) and a blood culture isolate of S. pneumoniae (SP2) were used in the assays. Cytokines were quantified by BioRad bead assay and Luminex 200. IFN-γ priming enhanced cytokine responses. S. pneumoniae ATCC 49619 induced lower responses than SP2 for IL-1β, IL-6, TNF-α. A. otitidis LW 27 elicited higher IL-1β and TNF-α responses than either pneumococcal isolate. Small green colony types of A. otitidis induced higher responses than large white colony types for IL-8 and IL-1β. The hypothesis that A. otitidis elicits cytokines observed in middle ear effusions was supported; the need to use recent clinical isolates in studies of pathogenesis was highlighted.

Viral-bacterial interactions in acute otitis media

Acute otitis media (AOM) is a polymicrobial disease, which usually occurs as a complication of viral upper respiratory tract infection (URI). While respiratory viruses alone may cause viral AOM, they increase the risk of bacterial middle ear infection and worsen clinical outcomes of bacterial AOM. URI viruses alter Eustachian tube (ET) function via decreased mucociliary action, altered mucus secretion and increased expression of inflammatory mediators among other mechanisms. Transient reduction in protective functions of the ET allows colonizing bacteria of the nasopharynx to ascend into the middle ear and cause AOM. Advances in research help us to better understand the host responses to viral URI, the mechanisms of viral-bacterial interactions in the nasopharynx and the development of AOM. In this review, we present current knowledge regarding viral-bacterial interactions in the pathogenesis and clinical course of AOM. We focus on the common respiratory viruses and their established role in AOM.

Respiratory syncytial virus promotes Moraxella catarrhalis-induced ascending experimental otitis media

Otitis media (OM) is a polymicrobial disease wherein prior or concurrent infection with an upper respiratory tract virus plays an essential role, predisposing the middle ear to bacterial invasion. In episodes of acute bacterial OM, respiratory syncytial virus (RSV) is the most commonly isolated virus and thus serves as an important co-pathogen. Of the predominant bacterial agents of OM, the pathogenesis of disease due to Moraxella catarrhalis is the least well understood. Rigorous study of M.catarrhalis in the context of OM has been significantly hindered by lack of an animal model. To bridge this gap, we assessed whether co-infection of chinchillas with M. catarrhalis and RSV would facilitate ascension of M. catarrhalis from the nasopharynx into the middle ear. Chinchillas were challenged intranasally with M. catarrhalis followed 48 hours later by intranasal challenge with RSV. Within 7 days, 100% of nasopharynges were colonized with M. catarrhalis and homogenates of middle ear mucosa were also culture-positive. Moreover, within the middle ear space, the mucosa exhibited hemorrhagic foci, and a small volume of serosanguinous effusion was present in one of six ears. To improve upon this model, and based on epidemiologic data, nontypeable Haemophilus influenzae (NTHI) was included as an additional bacterial co-pathogen via intranasal administration four days before M. catarrhalis challenge. With this latter protocol, M. catarrhalis was cultured from the nasopharynx and middle ear homogenates of a maximum of 88% and 79% animals, respectively, for up to 17 days after intranasal challenge with M. catarrhalis. Additionally, hemorrhagic foci were observed in 79% of middle ears upon sacrifice. Thus, these data demonstrated that co-infection with RSV and NTHI predisposed to M. catarrhalis-induced ascending experimental OM. This model can be used both in studies of pathogenesis as well as to investigate strategies to prevent or treat OM due to M. catarrhalis.

Viral-bacterial co-infection in Australian Indigenous children with acute otitis media

Background

Acute otitis media with perforation (AOMwiP) affects 40% of remote Indigenous children during the first 18 months of life. Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis are the primary bacterial pathogens of otitis media and their loads predict clinical ear state. Our hypothesis is that antecedent respiratory viral infection increases bacterial density and progression to perforation.

Methods

A total of 366 nasopharyngeal swabs from 114 Indigenous children were retrospectively examined. A panel of 17 respiratory viruses was screened by PCR, and densities of S. pneumoniae, H. influenzae and M. catarrhalis were estimated by quantitative real time PCR. Data are reported by clinical ear state.

Results

M. catarrhalis (96%), H. influenzae (91%), S. pneumoniae (89%) and respiratory viruses (59%) were common; including rhinovirus (HRV) (38%), polyomavirus (HPyV) (14%), adenovirus (HAdV) (13%), bocavirus (HBoV) (8%) and coronavirus (HCoV) (4%). Geometric mean bacterial loads were significantly higher in children with acute otitis media (AOM) compared to children without evidence of otitis media. Children infected with HAdV were 3 times more likely (p < 0.001) to have AOM with or without perforation.

Conclusion

This study confirms a positive association between nasopharyngeal bacterial load and clinical ear state, exacerbated by respiratory viruses, in Indigenous children. HAdV was independently associated with acute ear states.

Isolation of Alloiococcus otitidis from Indigenous and non-Indigenous Australian children with chronic otitis media with effusion

During the last decade Alloiococcus otitidis has been identified in specimens from patients with chronic otitis media with effusion. Whereas most of those studies employed molecular techniques, we used minor modifications of conventional microbiological methods to isolate and identify A. otitidis in samples obtained from 20/50 (40%) children referred for myringotomy. Alloiococcus otitidis was isolated from 10/22 (45%) Indigenous and 10/28 (36%) non-Indigenous children. This is the first report of isolation of A. otitidis from Australian children with chronic otitis media. All isolates were sensitive to penicillin, but 14/20 (70%) of the isolates were resistant or partially resistant to erythromycin as assessed by the E-test.

Purification of IgD from human serum--a novel application of recombinant M. catarrhalis IgD-binding protein (MID)

Moraxella catarrhalis IgD-binding protein (MID) is a multimeric outer membrane protein belonging to the family of autotransporters. The IgD-binding domain of MID is located between amino acids MID 962-1200 and binds to amino acids 198-224 of the IgD C(H)1 region. In the present study, we describe a method to purify IgD from serum with high levels of IgD using a two-step affinity chromatography process. The first step involves depletion of MID-specific antibodies of all classes from serum using the non-IgD-binding fragment MID(1000-1200). This step is followed by selective capture of IgD with MID(962-1200). Furthermore, we demonstrate that the eluted IgD is pure, intact and functional for use in downstream applications. Our approach reduces the non-specificity commonly associated with lectin-based IgD purification regimes that rely on glycosylation of the IgD molecule.

The IgD CH1 region contains the binding site for the human respiratory pathogenMoraxella catarrhalis IgD-binding protein MID

The Moraxella catarrhalis IgD-binding protein (MID) has a unique specificity for human IgD, and the sequence with maximal IgD binding is located within the amino acids MID962-1200. In the present paper, we examined the MID binding site on IgD using a series of recombinant Ig. Full-length IgD, IgD F(ab')2, and an IgD F(ab') C290R mutant lacking the inter-heavy-chain cysteine 290 were manufactured. Furthermore, a series of IgD/IgG chimeras were constructed. ELISA, dot blot and flow cytometry were used to study the binding of purified Ig to native MID, recombinant MID962-1200 or to Moraxella with or without MID. MID962-1200 bound both the IgD F(ab')2 and F(ab') C290R, indicating that the binding occurred independently of antibody structure. When amino acids 157-224 of the IgD CH1 region were substituted with IgG sequences, binding by M. catarrhalis or recombinant MID962-1200 was abolished. Subsequent smaller substitutions of IgD CH1 157-224 with IgG sequences led us to conclude that IgD CH1 amino acids 198-206 were crucial for the interaction between MID and IgD.

Identification and characterization of a novel outer membrane protein (OMP J) of Moraxella catarrhalis that exists in two major forms

Moraxella catarrhalis is a common commensal of the human respiratory tract that has been associated with a number of disease states, including acute otitis media in children and exacerbations of chronic obstructive pulmonary disease in adults. During studies to investigate the outer membrane proteins of this bacterium, two novel major proteins, of approximately 19 kDa and 16 kDa (named OMP J1 and OMP J2, respectively), were identified. Further analysis indicated that these two proteins possessed almost identical gene sequences, apart from two insertion/deletion events in predicted external loops present within the putative barrel-like structure of the proteins. The development of a PCR screening strategy found a 100% (96/96) incidence for the genes encoding the OMP J1 and OMP J2 proteins within a set of geographically diverse M. catarrhalis isolates, as well as a significant association of OMP J1/OMP J2 with both the genetic lineage and the complement resistance phenotype (Fisher's exact test; P < 0.01). Experiments using two DeltaompJ2 mutants (one complement resistant and the other complement sensitive) indicated that both were less easily cleared from the lungs of mice than were their isogenic wild-type counterparts, with a significant difference in bacterial clearance being observed for the complement-resistant isolate but not for its isogenic DeltaompJ2 mutant (unpaired Student's t test; P < 0.001 and P = 0.32). In this publication, we characterize a novel outer membrane protein of Moraxella catarrhalis which exists in two variant forms associated with particular genetic lineages, and both forms are suggested to contribute to bacterial clearance from the lungs.

The UspA2 protein of Moraxella catarrhalis is directly involved in the expression of serum resistance

Many strains of Moraxella catarrhalis are resistant to the bactericidal activity of normal human serum. Previous studies have shown that mutations involving the insertion of an antibiotic resistance cartridge into the M. catarrhalis uspA2 gene resulted in the conversion of a serum-resistant strain to a serum-sensitive phenotype. In the present study, the deletion of the entire uspA2 gene from the serum-resistant M. catarrhalis strain O35E resulted in a serum-sensitive phenotype and did not affect either the rate of growth or the lipooligosaccharide expression profile of this mutant. Inactivation of the classical complement pathway in normal human serum with Mg2+ and EGTA resulted in the survival of this uspA2 mutant. In contrast, blocking of the alternative complement pathway did not protect this uspA2 mutant from complement-mediated killing. To determine whether the UspA2 protein is directly involved in serum resistance, transformation and allelic exchange were used to replace the uspA2 gene in the serum-resistant strain O35E with the uspA2 gene from the serum-sensitive M. catarrhalis strain MC317. The resultant O35E transformant exhibited a serum-sensitive phenotype. Similarly, when the uspA2 gene from the serum-resistant strain O35E was used to replace the uspA2 gene in the serum-sensitive strain MC317, the MC317 transformant acquired serum resistance. The use of hybrid O35E-MC317 uspA2 genes showed that the N-terminal half of the O35E protein contained a 102-amino-acid region that was involved in the expression of serum resistance. In addition, when the uspA2 genes from strains O35E and MC317 were cloned and expressed in Haemophilus influenzae DB117, only the O35E UspA2 protein caused a significant increase in the serum resistance of the H. influenzae recombinant strain. These results prove that the UspA2 protein is directly involved in the expression of serum resistance by certain M. catarrhalis strains.