Sarah-Jane Haig

The adherence of six isolates of Mannheimia haemolytica to ovine bronchial epithelial cells (OBECs) was examined via immunofluorescence, scanning electron microscopy (SEM) and quantification assays; isolates used represented different capsular, outer membrane protein A (OmpA), and LPS types and species of isolation. The study revealed that both the capsular and LPS types of the isolates affected the level of adherence displayed; however there was no difference displayed in the level of adherence between ovine and bovine isolated strains, implying the presence of non-specific adhesins. Isolates were further tested for their ability to adhere to the extracellular matrix component, collagen, using a collagen-coated transwell insert seeded with OBECs, mimicking the in vivo environment of the respiratory tract. SEM results showed that all six isolates tested adhered to collagen. Additionally, the role of OmpA in attachment was investigated through inhibition assays using cross-absorbed OmpA-specific antibodies, with results showing that OmpA failed to have any effect on the level of attachment to OBECs achieved by all but the two virulent isolates tested, insinuating its potential as a virulence factor. Additionally, SEM revealed an unknown substance on the surface of the OBECs and decorating all six isolates. Subsequent analysis, entailing further SEM imaging and the growth of the isolates on Congo red agar indicated that this may be extracellular polysaccharide, implying that M. haemolytica possesses the potential to form biofilms, a previously undocumented ability.