Development of an ex vivo model to study adherence of Mannheimia haemolytica serovar 1 to mucosal tissues of the respiratory tract of cattle

Objective-To develop and validate an ex vivo model for study of adherence o f Mannheimia haemolytica (formerly Pasteurella haemolytica) to respiratory tract mucosa of cattle and to use this model to confirm adherence of M haem olytica serovar 1 (Mh1) to several relevant respiratory mucosal surfaces. Sample Population-Excised nasal, nasopharyngeal, turbinate, and tonsillar m ucosal tissue from the bovine upper respiratory tract. Procedure-Mh1 was radiolabeled by use of tritiated leucine. Various concent rations of labeled bacteria were incubated with bovine upper respiratory tr act tissues for various times. Tissue was washed to remove nonadherent bact eria, and percentage of bacteria adhered (percentage of adherence) was esti mated using radioactivity. Using an optimal inoculum concentration and incu bation time, percentage of Mh1 adherence was compared on nasal, nasopharyng eal, turbinate, and tonsillar mucosal tissue, and adherence to nasopharynge al tissue was confirmed by scanning and transmission electron microscopy. Results-The optimal Mh1 inoculum concentration was 1 x 10(7) colony forming units/ml and incubation time was 3 hours. Percentage of adherence of Mh1 t o nasopharyngeal tissue was greater than adherence to other tissue types. Conclusions and Clinical Relevance-The ex vivo model maintained the functio nal and structural integrity of bovine upper respiratory tract mucosa, as c onfirmed by light and electron microscopy. Electron microscopy revealed par ticipation of epithelial cell cilia and surface mucus in adherence of Mh1 t o nasopharyngeal tissue. Adherence of Mh1 was confirmed in repeated assays, indicating that this organism adheres to upper respiratory tract mucosa of cattle.