Otitis media (OM, middle ear infection) is the most common reason a child will be prescribed antibiotics and second most common reason a child will undergo surgery. Nontypeable Haemophilus influenzae (NTHi) is the most significant OM pathogen. New therapeutics are required to reduce NTHi disease burden, especially for Australian Indigenous children who have the highest OM rates in the world. Haemophilus haemolyticus (Hh) resides in the upper respiratory tract and is closely related to NTHi but is generally considered to be non-pathogenic. Hh is scarcely found in populations of high NTHi carriage, and we hypothesise that Hh and NTHi compete for niche space within the nasopharynx. Consequently, we are investigating whether Hh can be developed into a probiotic to interfere with NTHi colonisation and prevent subsequent disease.
We assessed the ability of an Hh strain isolated from the nasopharynx of a healthy child to study co-colonisation in an established NTHi-OM mouse-model. At 6-8 weeks of age, BALB/c mice were infected intranasally (i.n.) with 104.5 PFU of Influenza A Virus and 2 days later i.n. received either 2x106 CFU/mL of Hh or PBS. The following day, mice received 1x107 NTHi R2866 or PBS i.n. Mice were sacrificed on day 5, and nasal washings and middle ear tissue samples were collected and plated onto selective media to determine bacterial load.
Hh successfully colonised mouse nasal passages with 1.61x104 CFU/mL (+/- 8.75x103) present at day 5. Importantly, pre-colonisation with Hh significantly reduced the proportion of NTHi at 5 days compared with mice who received the PBS pre-treatment. To our knowledge, this is the first in vivo study of Hh, and the observation that Hh interferes with NTHi colonisation suggests potential for development of Hh to prevent NTHi disease. Future work will investigate whether interference is strain and/or species-specific.