Mucosal colonization of Mannheimia haemolytica capsular and adhesin mutants in cattle

Authors: Zakrzewicz, Anna; MENGHWAR, HARISH - Oak Ridge Institute For Science And Education (ORISE); Kanipe, Carly; BRIGGS, ROBERT - Retired ARS Employee; Chriswell, Bradley; Casas, Eduardo; Clawson, Michael; Tatum, Fred; Dassanayake, Rohana

Submitted to: Microbiology Spectrum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2025
Publication Date: 5/22/2025
Citation: Goldcamp, A.K., Menghwar, H., Kanipe, C.R., Briggs, R., Chriswell, B.O., Casas, E., Clawson, M.L., Tatum, F.M., Dassanayake, R.P. 2025. Mucosal colonization of Mannheimia haemolytica capsular and adhesin mutants in cattle. Microbiology Spectrum. Article e00684-25. https://doi.org/10.1128/spectrum.00684-25.
DOI: https://doi.org/10.1128/spectrum.00684-25

Interpretive Summary: Mannheimia haemolytica is a common bacteria found in the upper respiratory tract of cattle. It is believed that adhesins and capsule are important virulence determinants (in M. haemolytica) and involved in colonization. To test this, we conducted a calf challenge study to assess their role in colonization. We found that the capsule is important for long-term colonization and bacteria lacking adhesins may survive better than parent wildtype strain.

Technical Abstract: Mannheimia haemolytica is a normal inhabitant of the upper respiratory tract of ruminants and is associated with bovine respiratory disease (BRD). Polysaccharide capsule and surface adhesins are suggested to function in adherence and colonization of M. haemolytica to the mucosa of the upper respiratory tract. M. haemolytica serotype 1 (St1) mutant strains containing deletions of either the capsule biosynthetic gene cluster ('cap) or putative adhesin genes ('adh123) were created using a temperature-sensitive plasmid and tested for colonization in a calf challenge model. Two treatment groups were used in the study: Sham-Mh-BHV-1 (SMB; intranasal administration of cell culture lysate/supernatant (sham; S) four days before intranasal M. haemolytica (Mh) inoculation, and intranasal inoculation of bovine-herpesvirus-1 (BHV-1) 20 days post-Mh) and BHV-1-Mh-Sham (BMS; intranasal inoculation of BHV-1 four days before intranasal Mh inoculation and intranasal sham administration 20 days post-Mh). A mixture of wildtype M. haemolytica parent strain, 'cap, and 'adh123 mutants was included in the Mh inoculum. Animals were observed for clinical signs and nasal colonization for approximately 7 weeks. The 'adh123 mutant and parent strain colonized the nasopharynx, whereas 'cap mutant was not detected after one day-post inoculation. The 'adh123 mutant colonized the nasopharynx at significantly higher levels (p<0.0001) compared to wildtype. Higher colonization of 'adh123 was also found in palatine tonsils. These findings suggest a requirement of capsule in long-term colonization, and an advantage for 'adh123 in colonization over the parent strain.