Genetic diversity, virulence genes, and antimicrobial resistance of Moraxella bovoculi and Moraxella bovis from infectious bovine keratoconjunctivitis: insights from MALDI-TOF-MS, 16S rRNA analyses, and other ocular bacteria

Abstract

Background Moraxella bovis is the main etiological agent of infectious bovine keratoconjunctivitis (IBK). However, Moraxella bovoculi and other bacteria are also frequently isolated from IBK. The recurrent detection of M. bovoculi suggests a role in IBK, though its contribution remains unclear. This study aimed to characterize M. bovoculi and M. bovis isolates from IBK cases and evaluate the role of other ocular bacteria. Methods Eye swabs from cattle with keratoconjunctivitis were cultured and identified using MALDI-TOF MS, with 16S rRNA sequencing for confirmation. Virulence gene analysis targeted six genes in M. bovis (omp79, mbxA, fur, plb, pil, tolC) and three in M. bovoculi (pilA, mbvA, omp79). Antimicrobial susceptibility was evaluated using the Kirby-Bauer disk diffusion method. Results Forty-seven isolates were obtained, with Moraxella spp. predominant. Fifteen were identified as M. bovoculi and nine as M. bovis. Sequencing largely confirmed MALDI-TOF results with minor discrepancies. Virulence screening showed M. bovoculi consistently carried pilA and variably mbvA and omp79, whereas M. bovis harbored a broader set (omp79, mbxA, fur, plb, pil, tolC). Antimicrobial testing indicated a reduced susceptibility trend in M. bovoculi, particularly to fluoroquinolones, tetracyclines, and phenicols, whereas M. bovis exhibited a relatively higher susceptibility tendency. Furthermore, the isolation of non-Moraxella bacteria highlights their potential role as opportunistic pathogens in IBK. Conclusion Moraxella isolates from IBK exhibit marked genetic diversity and distinct virulence repertoires, with M. bovoculi showing a trend toward decreased susceptibility. The detection of additional ocular bacteria highlights the multifactorial nature of IBK. These findings underscore the need for accurate diagnostics, antimicrobial stewardship, and exploration of alternative approaches such as vaccines for controlling IBK.