Fluoroquinolone resistance in Haemophilus influenzae from nursing home residents in Taiwan: correlation of MICs and mutations in QRDRs

Epidemic Trends and Biofilm Formation Mechanisms of Haemophilus influenzae: Insights into Clinical Implications and Prevention Strategies

Haemophilus influenzae (H. influenzae) is a significant pathogen responsible for causing respiratory tract infections and invasive diseases, leading to a considerable disease burden. The Haemophilus influenzae type b (Hib) conjugate vaccine has notably decreased the incidence of severe infections caused by Hib strains, and other non-typable H. influenzae (NTHi) serotypes have emerged as epidemic strains worldwide. As a result, the global epidemic trends and antibiotic resistance characteristics of H. influenzae have been altered. Researches on the virulence factors of H. influenzae, particularly the mechanisms underlying biofilm formation, and the development of anti-biofilm strategies hold significant clinical value. This article provides a summary of the epidemic trends, typing methods, virulence factors, biofilm formation mechanisms, and prevention strategies of H. influenzae. The increasing prevalence of NTHi strains and antibiotic resistance among H. influenzae, especially the high β-lactamase positivity and the emergence of BLNAR strains have increased clinical difficulties. Understanding its virulence factors, especially the formation mechanism of biofilm, and formulating effective anti-biofilm strategies may help to reduce the clinical impact. Therefore, future research efforts should focus on developing new approaches to prevent and control H. influenzae infections.

Emergence of Haemophilus influenzae with low susceptibility to quinolones isolated from pediatric patients in Japan

INTRODUCTION

In 2010, oral fluoroquinolone tosufloxacin (TFX) granules were released as the first oral respiratory quinolone for children in Japan.

METHODS

To investigate the recent trend of H. influenzae strains with low susceptibility to quinolones in children, we analyzed the gene sequences of quinolone resistance-determining regions (QRDRs) of gyrA, gyrB, parC, and parE of 23 clinical isolates from 15 patients aged <15 years with an MIC of ≥0.5 μg/mL for TFX from 2010 to 2018.

RESULTS

Amino acid substitutions were observed in both GyrA and ParC in 13 strains (81%, 13/16), except two strains with a TFX MIC of 0.5 μg/mL with amino acid substitution in only GyrA and one strain with a TFX MIC of 1 μg/mL with no amino acid substitution. Four ST422 strains were observed in 2018, the detection age range was wide (0-7 years), and the residential city was varied. A total of 3/15 patients had a clear history of TFX treatment.

CONCLUSIONS

Even for the strain with an MIC of 0.5 μg/mL for TFX, it is highly possible that it harbors a mutation in gyrA, which is the first step toward quinolone resistance, and it may also harbor mutations in both gyrA and parC. Furthermore, several specific sequence type quinolone-resistant H. influenzae strains, particularly ST422, may be widespread among children in Japan. It is necessary to investigate changes in resistance both at the MIC and gene levels. The continuous monitoring of strains and the use of antimicrobial drugs in treatment should be carefully observed.

Whole-genome sequence of Haemophilus influenzae ST422 outbreak clone strain 2018-Y40 with low quinolone susceptibility isolated from a paediatric patient

OBJECTIVES

In recent years, Haemophilus influenzae strains with reduced susceptibility to quinolones have emerged and spread in Japan. In addition, an outbreak of isolates with low quinolone susceptibility among paediatric patients has also been reported. The aim of this study was to determine the molecular characteristics of an H. influenzae ST422 outbreak clone with low quinolone susceptibility isolated from a paediatric patient using whole-genome sequencing.

METHODS

The PacBio RS II platform was used for sequencing, and de novo assembly was performed using RS HGAP assembly version 3.0. The assembled sequences were annotated using DFAST version 1.1.15. Prophages were estimated using the PHASTER program.

RESULTS

Whole-genome sequencing of H. influenzae ST422 isolate 2018-Y40 revealed that the genome size was 1 957 393bp, comprising 1 926 protein-coding sequences, 19 rRNAs, and 57 tRNAs, with a guanine-cytosine (GC) content of 38.2%. This isolate had no relevant exogenous antimicrobial-resistant genes. However, amino acid substitutions were found in both GyrA and ParC, as well as at the 385th and 526th amino acid residues in penicillin-binding protein 3. In addition, four intact prophage regions and one incomplete prophage region were found.

CONCLUSIONS

The whole-genome sequence of H. influenzae 2018-Y40 indicated that this clone emerged as a result of extensive genomic rearrangement by integration of multiple phages. As genomic rearrangement occasionally leads to a new phenotype, this clone could have acquired antimicrobial resistance and diversification via rearrangement events. These findings can form a basis to help clarify the mechanisms of low quinolone susceptibility and the spread of this outbreak clone.