Antibiotic modulation of mucins in otitis media; should this change our approach to watchful waiting?

Abstract

Background

Gel-forming mucins (GFMs) play important roles in otitis media (OM) pathogenesis. Increased mucin expression is activated by pathogens and proinflammatory cytokines. Bacterial biofilms influence inflammation and resolution of OM and may contribute to prolonged mucin production. The influence of specific pathogens on mucin expression and development of chronic OM with effusion (OME) remains an area of significant knowledge deficit.

Objectives

To assess the relationship between GFM expression, specific pathogens, middle ear mucosal (MEM) changes, biofilm formation, and antibiotic utilization.

Methods

Mixed gender chinchillas were inoculated with nontypeable Haemophilus influenzae (NTHi) strain 86028NP or Streptococcus pneumoniae (SP) strain TIGR4 via transbulla injection. Antibiotic was administered on day 3–5 post inoculation. GFM expression was measured by quantitative PCR. Biofilm formation was identified and middle ear histologic changes were measured.

Results

SP infection resulted in higher incidence of biofilm and ME effusion compared with NTHi infection. However, NTHi persisted in the ME longer than SP with no substantive bacterial clearance detected on day 10 compared with complete bacterial clearance on day 10 for 50–60% of the SP-infected chinchillas. Both infections increased MEM inflammatory cell infiltration and thickening. NTHi upregulated the Muc5AC, Muc5B and Muc19 expression on day 10 (p = 0.0004, 0.003, and 0.002 respectively). SP-induced GFM upregulations were trended toward significant. In both NTHi and SP infections, the degree of GFM upregulation had a direct relationship to increased MEM hypertrophy, inflammatory cell infiltration and biofilm formation. Antibiotic treatment reduced the incidence of ME effusion and biofilm, limited the MEM changes and reversed the GFM upregulation. In NTHi infection, the rate of returning to baseline level of GFMs in treated chinchillas was quicker than those without treatment.

Conclusions

In an animal model of OM, GFM genes are upregulated in conjunction with MEM hypertrophy and biofilm formation. This upregulation is less robust and more quickly ameliorated to a significant degree in the NTHi infection with appropriate antibiotic therapy. These findings contribute to the understanding of pathogen specific influences on mucin expression during OM pathogenesis and provide new data which may have implications in clinical approach for OM treatment.

Introduction

Otitis media (OM), bacterial and/or viral infection of the middle ear (ME), continues to be the most frequently diagnosed pediatric illness in the US. Although often self-limited, without proper treatment, OM may cause severe complications. Approximately 30–40% of OM children develop recurrent episodes which require multiple physician visits, multiple courses of antibiotics, and the potential need for surgical intervention. In another subset of OM children, otitis media with effusion (OME) develops and can become chronic in nature and impact overall hearing and speech and language development [[1], [2], [3]].

One of the main characteristics of OM is increased mucin production by middle ear mucosal (MEM) epithelium [[4], [5], [6]]. These mucins are secreted at increased quantity compared to steady-state to protect the underlying MEM from pathogen invasion and adherence and to assist in pathogen removal through mucociliary clearance. However, the increased mucin production can persist following the resolution of the acute infection, become detrimental to mucociliary clearance and ultimately lead to persisting and substantive hearing loss [5]. Each mucin has unique characteristics and changes in the production of any mucin can change the composition, function and viscosity of the mucous overlaying the epithelium. The secretory gel forming mucins (GFM) identified in the MEM are MUC2, MUC5AC, MUC5B and MUC19 [5].

Increased mucin expression is activated by bacteria [7] and proinflammatory cytokines which are upregulated during an episode of OM [[8], [9], [10], [11], [12], [13]]. Nontypeable Haemophilus influenzae (NTHi) and Streptococcus pneumoniae (SP), the subject of this investigation, are recognized as primary causative OM pathogens. There are differences in the virulence and ME impact between pathogen families such as SP and NTHi and, in addition, each of these pathogens has numerous strains or serotypes which also have been shown to differentially impact any given patient with OM [14,15].

Biofilms have been well-documented as an important component of OM pathogenesis. NTHi and SP coexist within biofilm communities during chronic and recurrent infection [16,17]. The prevalence of biofilms influences inflammation and resolution of OM and may contribute to prolonged mucin production [[18], [19], [20], [21]].

A paucity of data exists in well-controlled scientific experiments to better understand the host molecular and genetic response to specific pathogens, differences between pathogens and the implications of these differences on the concepts related to patient treatment. Specific pathogen influences on mucin production and development of chronic OM remains an area of significant knowledge deficit. This report represents the first in vivo controlled study to explore results related to the two most common bacterial OM pathogens and their influence on mucin gene expression, MEM changes and the impact of antibiotic therapy on these changes.