Abstract
Non‐typeable Haemophilus influenzae (NTHi) is a major pathogen causing acute otitis media (AOM). The relationship between the cellular content of the middle ear fluid (MEF) during AOM and infection of NTHi is poorly understood. Using the Junbo mouse, a characterised NTHi infection model, we analysed the cellular content of MEF and correlated the data with NTHi titres. The MEF of the Junbo mouse was heterogeneous between ears and was graded from 1 to 5; 1 being highly serous/clear and 5 being heavily viscous/opaque. At seven‐day post‐intranasal inoculation, NTHi was not found in grade‐1 or 2 fluids, and the proportion of MEF that supported NTHi increased with the grade. Analyses by flow cytometry indicated that the cellular content was highest in grade‐4 and 5 fluids, with a greater proportion of necrotic cells and a low‐live cell count. NTHi infection of the middle ear increased the cell count and led to infiltration of immune cells and changes in the cytokine and chemokine levels. Following NTHi inoculation, high‐grade infected MEFs had greater neutrophil infiltration whereas monocyte infiltration was significantly higher in serous noninfected low‐grade fluids. These data underline a role for immune cells, specifically monocytes and neutrophils, and cell necrosis in NTHi infection of the Junbo mouse middle ear.
Highlights
Otitis media (OM) is characterised by inflammation of the middle ear and is the most common cause of hearing impairment in children (MacArthur, Hausman, Kempton, Lighthall, & Trune, 2012)
The current study investigates the nature of the bulla fluids in the Junbo mouse and its association with middle ear infection by nontypeable Haemophilus influenzae (NTHi), a prevalent pathogen causing acute otitis media (AOM) (Barkai, Leibovitz, Givon‐Lavi, & Dagan, 2009; Sierra et al, 2011) in children
AOM is characterised by inflammation and the formation of fluid in the middle ear (Vergison, 2008); characteristics of this fluid typically play a significant part in defining the severity and chronicity of OM (Lin et al, 2003; Massa et al, 2015)
Summary
Otitis media (OM) is characterised by inflammation of the middle ear and is the most common cause of hearing impairment in children (MacArthur, Hausman, Kempton, Lighthall, & Trune, 2012) Based on variables such as the chronicity of inflammation and the state of middle ear (bulla) fluid, OM is classified into different categories (Myburgh, van Zijl, Swanepoel, Hellström, & Laurent, 2016). Persistence of bacteria/ virus/bacterial material in the middle ear might initiate the inflammatory response that leads to recurrence of OM, and the cellular content of the bulla fluid is likely a significant factor that influences clearance (Forséni, et al, 1999). In the current study, using a Junbo mouse model of OM, we analysed the correlation between the cellular content of the middle‐ear fluid against the ability of NTHi to infect the preinflamed middle ear. We show that the type of immune cell and its functional state both contribute to the NTHi infection observed in the inflamed middle ear of Junbo mice
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