Relatedness of type IV pilin PilA amongst geographically diverse Moraxella bovoculi isolated from cattle with infectious bovine keratoconjunctivitis

Abstract

<b>Introduction.</b> <i>Moraxella bovoculi</i> is frequently isolated from the eyes of cattle with infectious bovine keratoconjunctivitis (IBK; pinkeye). As with <i>M. bovis,</i> which has been causally linked to IBK, <i>M. bovoculi</i> expresses an RTX (repeats in the structural toxin) cytotoxin that is related to <i>M. bovis</i> cytotoxin. Pilin, another pathogenic factor in <i>M. bovis</i>, is required for corneal attachment. Seven antigenically distinct pilin serogroups have been described in <i>M. bovis</i>.<b>Hypothesis/Gap Statement.</b> Multiple different serogroups exist amongst type IV pilin encoded by <i>M. bovis</i>, however, it is not known whether <i>M. bovoculi</i> exhibits a similar degree of diversity in type IV pilin that it encodes.<b>Aim.</b> This study was done to characterize a structural pilin (PilA) encoded by <i>M. bovoculi</i> isolated from cases of IBK to determine if diversity exists amongst PilA sequences.<b>Methodology.</b> Ninety-four isolates of <i>M. bovoculi</i> collected between 2002 and 2017 from 23 counties throughout California and from five counties in four other Western states were evaluated.<b>Results.</b> DNA sequencing and determination of deduced amino acid sequences revealed ten (designated groups A through J) unique PilA sequences that were ~96.1-99.3 % identical. Pilin groups A and C matched previously reported putative PilA sequences from <i>M. bovoculi</i> isolated from IBK-affected cattle in the USA (Virginia, Nebraska, and Kansas) and Asia (Kazakhstan). The ten pilin sequences identified were only ~74-76 % identical to deduced amino acid sequences of putative pilin proteins identified from the previously reported whole-genome sequences of <i>M. bovoculi</i> derived from deep nasopharyngeal swabs of IBK-asymptomatic cattle.<b>Conclusions.</b> Compared to the diversity reported between structural pilin proteins amongst different serogroups of <i>M. bovis</i>, <i>M. bovoculi</i> PilA from geographically diverse isolates derived from IBK-affected cattle are more conserved.