Highly transformable Haemophilus influenzae as a potential amplifier of quinolone resistance dissemination

BACKGROUND: Horizontal gene transfer in Haemophilus spp. is associated with antimicrobial resistance development. Recently, a relationship between quinolone resistance and this transfer has been reported. This study aimed to investigate the mechanisms underlying quinolone resistance spread by focusing on both homogeneous and heterogeneous transfer to H. influenzae. METHODS: Quinolone-resistant strains of three Haemophilus spp., H. influenzae, H. haemolyticus, and H. parainfluenzae, were used as resistant donors. The H. influenzae laboratory strain Rd and the highly transformable strains 2017-22B and 2018-Y41 were used as recipients. Horizontal transfer assays were performed using genomic DNA from resistant donors or resulting transformants. RESULTS: Horizontal transfer assays demonstrated that quinolone resistance was transferred from the genomic DNA of H. influenzae and H. haemolyticus to all recipient strains. In contrast, resistance from H. parainfluenzae genomic DNA was transferred only to the strains with higher transformability. In all cases, transfer efficiency was higher when DNA from the transformants was used than when DNA from the original strain was used. Notably, genomic DNA from transformants obtained by transferring resistance from H. parainfluenzae to highly transformable H. influenzae strains transformed Rd into a quinolone-resistant variant. Furthermore, no significant differences in growth were observed between the parent strains and transformants. CONCLUSIONS: Our findings suggest that highly transformable strains, owing to their enhanced transformation capacity and retained fitness, may facilitate or amplify the dissemination of quinolone resistance under experimental conditions.