Alternative quinolone-resistance pathway caused by simultaneous horizontal gene transfer in Haemophilus influenzae

Unique and Ingenious Mechanisms Underlying Antimicrobial Resistance and Spread of Haemophilus influenzae

Antimicrobial resistance (AMR) is a serious global concern. AMR pathogens are found in hospitals and communities. Haemophilus influenzae is a common pathogen associated with community-acquired infections. H. influenzae infections are usually treated with β-lactams, macrolides, and quinolones. However, the drug-resistant strains have emerged. The resistance mechanisms of H. influenzae are complex but are roughly characterized by the acquisition of a mutation in antimicrobial-targeting genes and exogenous resistant genes. Generally, the former cannot be transferred horizontally to a susceptible strain. However, several studies have demonstrated that, in the case of H. influenzae, both the former and the latter can be transferred horizontally. In this review, we provide an overview of the bacterial features and antimicrobial resistance of H. influenzae. We also summarize the unique and ingenious antimicrobial resistance mechanisms used by this pathogen based on the findings of recent studies. These are expected to facilitate the understanding of AMR pathogens in the community and develop strategies to combat infections.

The Association between Transformation Ability and Antimicrobial Resistant Potential in Haemophilus influenzae

The prevalence of quinolone low-susceptible Haemophilus influenzae has increased in Japan. Low quinolone susceptibility is caused by point mutations in target genes; however, it can also be caused by horizontal gene transfer via natural transformation. In this study, we examined whether this horizontal gene transfer could be associated with resistance to not only quinolones but also other antimicrobial agents. Horizontal transfer ability was quantified using the experimental transfer assay method for low quinolone susceptibility. Further, the association between horizontal transfer ability and resistance to β-lactams, the first-choice drugs for H. influenzae infection, was investigated. The transformation efficiency of 50 clinical isolates varied widely, ranging from 102 to 106 colony forming unit (CFU) of the colonies obtained by horizontal transfer assay. Efficiency was associated with β-lactam resistance caused by ftsI mutations, indicating that strains with high horizontal transfer ability acquired quinolone low-susceptibility as well as β-lactam resistance more easily. Strains with high transformation efficiency increased the transcript level of comA, suggesting that enhanced com operon was associated with a high DNA uptake ability. Overall, this study revealed that the transformation ability of H. influenzae was associated with multiple antimicrobial resistance. Increase in the number of strains with high horizontal transformation ability has raised concerns regarding the rapid spread of antimicrobial-resistant H. influenzae.