Nontypeable Haemophilus influenzae (NTHi) is the major pathogen in otitis media (OM, middle ear infection). Colonisation of the nasopharynx with NTHi is a prerequisite to developing OM. Therefore therapies that prevent NTHi colonisation may prevent OM. Microbial interference involves the use of commensals to compete with pathogens to beneficially alter the host microflora. We previously demonstrated that pre-treatment of human respiratory epithelium with Haemophilus haemolyticus, a closely related commensal of NTHi, can prevent NTHi colonisation and infection of the epithelial cells. We have now assessed whether a rodent commensal Muribacter muris (from the same family as H. haemolyticus and NTHi) can prevent NTHi OM in vivo.
Methods: Using the murine NTHi OM ascension model, BALB/c mice were intranasally pre-treated with either M. muris (5x107 colony-forming units, CFU) (n=12) or saline (n=15) on Day 0. On Day 1, mice were challenged with 1x104.5 plaque-forming units of Influenza A virus (strain MEM, H3N2) followed by a Day 3 intranasal challenge with 5x107 CFU of NTHi (strain R2866Specr). Mice were monitored daily and scored clinically. Nasal washes and middle ear bullae were collected on Day 6. Homogenised ear tissue and nasal washes were plated onto selective media.
Results: Intranasal treatment of mice with M. muris reduced NTHi colonisation from 6 x 105 CFU/mL to 9 x 103 CFU/mL, p=0.0004. M. muris pre-treatment also prevented development of NTHi OM, with 8% (1/12) of pre-treated mice developing OM compared with 67% (8/12) of untreated controls, p=0.0682. The inflammatory response to NTHi was reduced in pre-treated mice, with lower KC (IL-8 homolog) levels in the middle ear compared with controls (p=0.0058). Weight loss was reduced (10.4% versus 13.8%; p=0.0006) and clinical scores improved (5.5 versus 7.2; p<0.00001) in pre-treated mice.
Conclusion: We have demonstrated that microbial interference can prevent NTHi OM in a murine model. Human challenge studies using microbial interference of NTHi are warranted to reduce the global burden of OM.