Infectivity and virulence of Australian strains of Moraxella bovis for the murine and bovine eye in relation to pilus serogroup sub‐unit size and degree of piliation

Abstract

The degree of piliation of 29 haemolytic and 4 non-haemolytic Australian strains of Moraxella bovis representing 7 different pilus antigen groups was determined. The infectivity and virulence for the eye was measured in steroid-treated mice and in cattle. Non-piliated strains failed to infect the murine eye. Most moderately or heavily piliated strains reproducibly produced the highest infectivity and virulence scores in mice when compared with lightly or very lightly piliated strains (p less than 0.05). Non-haemolytic, piliated strains were infective and in one instance virulent for mice. Almost similar levels of infectivity and virulence were observed for 7 representative haemolytic strains tested in both cattle and mice. The relative molecular weight of pilin sub-units was compared using sodium dodecyl-sulphate polyacrylamide gel electrophoresis. Three classes of pili, alpha, beta and gamma of ascending sub-unit size were identified among the 7 pilus antigen serogroups. Pilin sub-unit size bore no relationship to the degree of piliation but most strains that were highly virulent in mice and cattle expressed alpha and gamma sub-units. Some strains appeared capable of switching from alpha to beta or form beta to gamma sub-unit production.

Q pili enhance the attachment of Moraxella bovis to bovine corneas in vitro

“…1 that M. bovis Q piliated Epp63 bacteria attached significantly better than l-piliated or non-piliated isogenic variants of the same strain. This greater adherence capability correlates well with the prior observation that Q-piliated organisms are significantly more infectious than l-piliated or non-piliated variants of the same strain when inoculated into the eyes of calves (Ruehl et ai, 1988;Lepper and Power, 1988), and suggests an attachment role for Q pili per se, or for some factor associated with Q-piliation. Figure 1 also shows that a recombinant P. aeruginosa bacteria which elaborates M. bovis Q pili, but which no longer expresses PAK pili, attached significantly better than the PAK-pili-expressing P. aeruginosa parent strain.…”

Infectious bovine keratoconjunctivitis vaccine development

“…61 Further, a recombinant M bovis cytotoxin-ISCOM (immune stimulating complex) matrix adjuvanted vaccine establishes beneficial trends including longer times to first ulceration, faster healing times and the reduction of the cumulative proportion of naturally occurring IBK. 62 Additional virulence determinants Although type 4 pili and haemolysin are the virulence determinants substantively linked to M bovis pathogenicity, 14,16,19,43,63 in vitro studies have suggested that M bovis produces a number of other possible virulence determinants that include proteases, fibrinolysins and phospholipases. 11,12 These potentially conserved antigens provide further possibilities for vaccine development.…”

Molecular Characterization of a Secreted Enzyme with Phospholipase B Activity from Moraxella bovis

“…In vitro studies have suggested that M. bovis produces a number of virulence determinants, including type IV pili (3,23), a secreted hemolysin (28), proteases, fibrinolysins, and phospholipases (9). To date, only type IV pili and the hemolysin have been substantively linked to the virulence of M. bovis (4,10,16,17,20,26). Here we describe the molecular characterization of an M. bovis gene encoding a phospholipase B activity and discuss the role this enzyme may play in the virulence of this veterinary pathogen.…”

“…Previous studies have shown that the type IV pili produced by M. bovis play a fundamental role in bacterial colonization of the bovine eye and mediate the essential first step in the pathogenic process that leads to disease (20). Following adhesion, secondary virulence factors are presumed to cause the clinical damage observed as pitting on the corneal surface (18).…”

“…We propose that the PLB from M. bovis is a member of the GDSL family and as such may play a role in the pathogenesis of the IBK infection. The precise nature of this role will be investigated by constructing a plb mutant and testing the pathogenicity of the mutant in the bovine IBK model system (20).…”