Abstract
Mannheimia haemolytica is the primary bacterial species associated with respiratory disease of ruminants. A lack of cost-effective, reproducible models for the study of M. haemolytica pathogenesis has hampered efforts to better understand the molecular interactions governing disease progression. We employed a highly optimised ovine tracheal epithelial cell model to assess the colonisation of various pathogenic and non-pathogenic M. haemolytica isolates of bovine and ovine origin. Comparison of single representative pathogenic and non-pathogenic ovine isolates over ten time-points by enumeration of tissue-associated bacteria, histology, immunofluorescence microscopy and scanning electron microscopy revealed temporal differences in adhesion, proliferation, bacterial cell physiology and host cell responses. Comparison of eight isolates of bovine and ovine origin at three key time-points (2 h, 48 h and 72 h), revealed that colonisation was not strictly pathogen or serotype specific, with isolates of serotype A1, A2, A6 and A12 being capable of colonising the cell layer regardless of host species or disease status of the host. A trend towards increased proliferative capacity by pathogenic ovine isolates was observed. These results indicate that the host-specific nature of M. haemolytica infection may result at least partially from the colonisation-related processes of adhesion, invasion and proliferation at the epithelial interface.
Highlights
Mannheimia haemolytica is the primary bacterial species associated with respiratory disease of ruminants
We have shown that differentiated bovine bronchial epithelial cells (BBECs) support the colonisation of pathogenic M. haemolytica[28]
In order to allow the study of M. haemolytica disease progression in vitro, it was important that our model support the colonisation of disease-causing strains
Summary
Mannheimia haemolytica is the primary bacterial species associated with respiratory disease of ruminants. There has been a growing interest in the development of cost-effective, biologically relevant models to gain a more complete understanding of the molecular mechanisms underlying these pathogenic processes and the factors determining host-specificity of M. haemolytica With this in mind, our group have developed highly optimised in vitro tissue engineered models of both cattle and sheep respiratory epithelia[24,25,26,27]. We did not observe a strict pathotype or host-origin selectivity using this model, but the physiology of both tissue-adherent bacteria and the colonised host epithelia were different comparing pathogenic and non-pathogenic M. haemolytica isolates These findings have implications for future use of the model for the study of commensal respiratory species and agents of the respiratory disease complex
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