Infection rates, disease frequency, pilin gene rearrangement, and pilin expression in calves inoculated with Moraxella bovis pilin-specific isogenic variants

Abstract

SUMMARY Pili have been implicated as virulence factors that result in increased infcctivity of Moraxella bovis , the causative agent of infectious bovine keratoconjunctivitis (ibk). Healthy calves' eyes were inoculated with I- or Q-piliate or nonpiliate M bovis Epp63 to compare the pathogenicity of these isogenic variants. Pathogenicity was determined by the rate of persistent M bovis infection and the prevalence of clinical IBK. Inoculation with M bovis expressing the Q pili resulted in the highest frequency of infection and ibk, whereas I-piliate M bovis elicited a lower rate and nonpiliate M bovis did not result in infection. In vivo pilin gene rearrangement and pilin-type switching were evaluated by DNA hybridization and immunoblot. Gene rearrangement and type switching varied dependently, and were observed only in eyes inoculated with Q-piliate M bovis . This study suggests that Q pili are specific for colonization of bovine corneal epithelium, whereas I pili enable maintenance of an established infection.