β-Lactamase-non-producing ampicillin-resistant Haemophilus influenzae is acquiring multidrug resistance

Exploiting haem-iron dependence of nontypeable Haemophilus influenzae: an avenue for future therapeutic development

Nontypeable Haemophilus influenzae (NTHi) is a major respiratory pathogen that imposes a substantial disease burden, globally. Further amplifying the burden of NTHi-associated infections is the rapidly expanding spectrum and prevalence of antibiotic resistance, and the lack of an effective vaccination strategy. In 2017, the World Health Organization list of "priority pathogens", highlighted the urgent need for new therapeutic agents against NTHi. Consequently, alternative preventative or treatment approaches that do not rely on antibiotic susceptibility or stable vaccine targets are becoming more attractive. The nutritional dependency for haem/iron at all stages of NTHi pathogenesis exposes a vulnerability that may be exploited for the development of such therapies. This review explores the role of haem/iron in all facets of NTHi pathogenesis, the host-bacterial competition for this vital nutrient, and the therapeutic potential of strategies that interfere with its acquisition.

R, Baldaniya L, kaur J, Rani B, Beig M. Insights into Haemophilus macrolide resistance: A comprehensive systematic review and meta-analysis

BACKGROUND

Haemophilus spp., particularly Haemophilus influenzae, are major global pathogens causing various infections. Macrolides are crucial in treating these infections, but rising resistance to macrolides in Haemophilus spp. highlights the growing threat of antimicrobial resistance (AMR).

OBJECTIVE

This study aims to assess the prevalence of macrolide resistance in Haemophilus spp, across different global regions.

METHODS

A systematic literature search was conducted across PubMed, Embase, Web of Science, and Scopus databases from May 2015 to December 2023 to identify studies on macrolide resistance in Haemophilus spp. The review included English-language full-text articles that reported resistance proportions and sample sizes. Study quality was assessed using the JBI Critical Appraisal Tool. Statistical analysis was performed using a random-effects model using the metafor package in R.

RESULTS

A total of 10,114 articles were retrieved, and after a comprehensive evaluation, 15 studies (from 19 reports) met the eligibility criteria for inclusion in this systematic review and meta-analysis. Most studies (eight reports from three countries) focused on clarithromycin susceptibility, revealing a pooled prevalence of 7.2%. High heterogeneity was observed for azithromycin (I² = 96.31%, p < 0.001). Azithromycin resistance was higher than clarithromycin, with a resistance rate of 9.3% (nine reports), while erythromycin resistance was significantly higher at 79% (four reports). Subgroup analysis revealed significant variations in resistance prevalence based on geographic location and continent for azithromycin, erythromycin, and clarithromycin. Additionally, notable differences were observed in resistance rates depending on antimicrobial susceptibility testing (AST) methods and AST guidelines for both azithromycin and erythromycin. Clarithromycin resistance increased from 0.7% (2015-2019) to 12.6% (2020-2023).

CONCLUSION

The study underscores the significant challenges of macrolide resistance in treating Haemophilus spp. infections. Additionally, ongoing surveillance of resistance patterns and exploring contributing factors are crucial to enhancing treatment effectiveness.

Longitudinal Trend in Antimicrobial Susceptibility among Haemophilus influenzae: A Single-Centre Study in Japan

Haemophilus influenzae presents significant concerns regarding antimicrobial resistance. The circumstances surrounding H. influenzae have been changing owing to changes in antimicrobial usage. In the present study, to determine the current situation of H. influenzae, the antimicrobial susceptibility trends were investigated. In total, 21 clinical isolates were analyzed. Antimicrobial susceptibility measured using the broth dilution method was compared with that reported in previous studies at the same hospital. Quinolone low-susceptible isolates were further characterized by multi-locus sequence typing. Upon comparing the susceptibility data in 2022 with those in the past 15 years, the number of β-lactamase nonproducing ampicillin-resistant isolates was decreased. Regarding recent changes, β-lactam-susceptible isolates were found to have gradually increased every year. However, β-lactamase-producing isolates did not decrease. In particular, the ratio of β-lactamase-producing amoxicillin and clavulanic acid-resistant isolates in 2022 was the highest among all the years studied. Moreover, quinolone low-susceptible isolates were still present, suggesting that these isolates could have been indigenized in the community. Furthermore, a β-lactamase-producing amoxicillin and clavulanic acid-resistant isolate was found to have emerged among the quinolone low-susceptibility isolates. At first glance, these findings indicate that antimicrobial resistance has decreased among H. influenzae in clinical settings. However, β-lactamase-producing isolates and quinolone low-susceptible isolates have remained at a constant rate in the community.

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.

Molecular characterization of a novel putative pathogen, Streptococcus nakanoensis sp. nov., isolated from sputum culture

Reports of novel species of α-hemolytic Streptococcus have increased recently. However, limited information exists regarding the pathogenicity of these species, with the exception of Streptococcus pneumoniae and Streptococcus pseudopneumoniae. In this study, a quinolone-resistant α-Streptococcus strain, MTG105, was isolated from the sputum of a patient with pneumonia. This strain was first identified as S. pneumoniae at the hospital laboratory; however, it exhibited unique genetic features upon further analysis. Digital DNA-DNA hybridization and average nucleotide identity based on BLAST values from whole-genome sequencing revealed MTG105 to be a novel species closely related to S. pseudopneumoniae. Although MTG105 carried two copies of the pneumolysin gene, similar to S. pseudopneumoniae, this isolate exhibited susceptibility to optochin under both aerobic and 5% CO2 conditions. Notably, no biochemical features could be used to definitively identify this species. In an infection assay using organotypic lung tissue models, MTG105 induced epithelial damage comparable to that of S. pneumoniae and S. pseudopneumoniae, possibly suggesting its potential as a pathogenic α-Streptococcus. The natural transformation abilities of Streptococcus species facilitate their exchange of genes within the same genus, resulting in the existence of species with increasingly more diverse genome structures. Therefore, the identification of this species highlights the importance of monitoring the emergence of novel species exhibiting virulence and/or multidrug resistance. This isolate was proposed as a novel species, designated Streptococcus nakanoensis sp. nov. The type strain was MTG 105T (= JCM 35953T = CCUG 76894T).

IMPORTANCE

The genus Streptococcus encompasses a wide range of bacteria with more than 60 species. Recently, there has been a notable increase in reports of novel species of α-Streptococcus based on genomic analysis data. However, limited information exists regarding the pathogenicity of these species. In this study, a quinolone-resistant α-hemolytic Streptococcus strain, MTG105, was isolated from a patient with pneumonia. Genetic analysis revealed that this species was a novel species closely related to S. pseudopneumoniae. In an infection assay using organotypic lung tissue models, MTG105 induced epithelial damage comparable to that caused by S. pneumoniae and S. pseudopneumoniae, strongly suggesting its potential as a pathogenic α-Streptococcus. The natural transformation abilities of Streptococcus species facilitate gene exchange within the same genus, leading to the emergence of species with increasingly diverse genome structures. Therefore, the identification of this species underscores the importance of monitoring the emergence of novel species exhibiting virulence and/or multidrug resistance.

Genomic characterization of Haemophilus influenzae harbouring an exogenous resistance gene

Introduction. Reports of β-lactamase-producing Haemophilus influenzae are increasing worldwide.Aim. This study aimed to elucidate the molecular characteristics and evolution of β-lactamase-producing H. influenzae.Methodology. A total of 159 clinical isolates were characterized using multi-locus sequence typing. Antimicrobial resistance genes and integrative and conjugative element (ICE) types were identified through PCR and DNA sequencing. The genetic structure of ICE was further investigated using whole-genome sequencing.Results. Out of 159 clinical isolates, 20.8% (n=33) were β-lactamase producers. Thirteen sequence types (STs) were identified. ST 103, 155, 165 and 388 have been identified in previous studies, suggesting that strains with these STs tend to acquire the β-lactamase gene bla TEM-1. Among β-lactamase producers, 66.7% (n=22) of bla TEM-1 were located on ICE. The ICEs could be classified into two groups based on their sequence (types I and II). Among these strains, 2017-Y3 harboured a macrolide resistance gene, mef (A/E), in ICE. A comparative analysis of the ICE region of this strain and those from other countries suggested that each isolate was derived from ICE type I or II. These regions, including mef (A/E), were similar to those of Tn6822, which is commonly found in Streptococcus.Conclusions. This study revealed several STs associated with the acquisition of β-lactamase genes on ICEs. Additionally, ICE evolution involved the acquisition of exogenous genes. The accumulation of resistance genes in ICE raises concerns regarding the emergence of multidrug-resistant H. influenzae.

Development and implementation of a core genome multilocus sequence typing scheme for Haemophilus influenzae

Haemophilus influenzae is part of the human nasopharyngeal microbiota and a pathogen causing invasive disease. The extensive genetic diversity observed in H. influenzae necessitates discriminatory analytical approaches to evaluate its population structure. This study developed a core genome multilocus sequence typing (cgMLST) scheme for H. influenzae using pangenome analysis tools and validated the cgMLST scheme using datasets consisting of complete reference genomes (N = 14) and high-quality draft H. influenzae genomes (N = 2297). The draft genome dataset was divided into a development dataset (N = 921) and a validation dataset (N = 1376). The development dataset was used to identify potential core genes, and the validation dataset was used to refine the final core gene list to ensure the reliability of the proposed cgMLST scheme. Functional classifications were made for all the resulting core genes. Phylogenetic analyses were performed using both allelic profiles and nucleotide sequence alignments of the core genome to test congruence, as assessed by Spearman's correlation and ordinary least square linear regression tests. Preliminary analyses using the development dataset identified 1067 core genes, which were refined to 1037 with the validation dataset. More than 70% of core genes were predicted to encode proteins essential for metabolism or genetic information processing. Phylogenetic and statistical analyses indicated that the core genome allelic profile accurately represented phylogenetic relatedness among the isolates (R 2 = 0.945). We used this cgMLST scheme to define a high-resolution population structure for H. influenzae, which enhances the genomic analysis of this clinically relevant human pathogen.

Tolerance to Haemophilus influenzae infection in human epithelial cells: Insights from a primary cell-based model

Haemophilus influenzae is a human respiratory pathogen and inhabits the human respiratory tract as its only niche. Despite this, the molecular mechanisms that allow H. influenzae to establish persistent infections of human epithelia are not well understood. Here, we have investigated how H. influenzae adapts to the host environment and triggers the host immune response using a human primary cell-based infection model that closely resembles human nasal epithelia (NHNE). Physiological assays combined with dualRNAseq revealed that NHNE from five healthy donors all responded to H. influenzae infection with an initial, 'unproductive' inflammatory response that included a strong hypoxia signature but did not produce pro-inflammatory cytokines. Subsequently, an apparent tolerance to large extracellular and intraepithelial burdens of H. influenzae developed, with NHNE transcriptional profiles resembling the pre-infection state. This occurred in parallel with the development of intraepithelial bacterial populations, and appears to involve interruption of NFκB signalling. This is the first time that large-scale, persistence-promoting immunomodulatory effects of H. influenzae during infection have been observed, and we were able to demonstrate that only infections with live, but not heat-killed H. influenzae led to immunomodulation and reduced expression of NFκB-controlled cytokines such as IL-1β, IL-36γ and TNFα. Interestingly, NHNE were able to re-activate pro-inflammatory responses towards the end of the 14-day infection, resulting in release of IL-8 and TNFα. In addition to providing first molecular insights into mechanisms enabling persistence of H. influenzae in the host, our data further indicate the presence of infection stage-specific gene expression modules, highlighting fundamental similarities between immune responses in NHNE and canonical immune cells, which merit further investigation.

Prevalence of piperacillin/tazobactam resistance in invasive Haemophilus influenzae in Germany

Background

Haemophilus influenzae (Hi) is a Gram-negative bacterium that may cause sepsis or meningitis, treatment of which mainly includes β-lactam antibiotics. Since 2019 EUCAST breakpoints for piperacillin/tazobactam have been available. Little is known about the prevalence and mechanisms of piperacillin/tazobactam resistance in Hi.

Objectives

To provide reliable prevalence data for piperacillin/tazobactam resistance in Hi in Germany, to evaluate different antibiotic susceptibility testing methods and to examine possible resistance mechanisms.

Methods

According to EUCAST breakpoints, the MIC for piperacillin/tazobactam resistance is >0.25 mg/L. All invasive Hi in Germany from 2019 were examined by gradient agar diffusion (GAD) for piperacillin/tazobactam susceptibility. Piperacillin/tazobactam broth microdilution (BMD), piperacillin GAD on tazobactam-containing agar [piperacillin GAD on Mueller-Hinton agar with horse blood (MH-F)/tazobactam) and piperacillin/tazobactam agar dilution (AD) were used for confirmation. Phenotypic testing was complemented by ftsI sequencing.

Results

Piperacillin/tazobactam GAD resulted in 2.9% (21/726) resistant Hi. BMD did not confirm piperacillin/tazobactam resistance. Two strains were found resistant by AD, of which one was also resistant using piperacillin GAD on MH-F/tazobactam. Overall, we found two strains with a piperacillin/tazobactam MIC >0.25 mg/L in at least two different tests (0.3%). Both were β-lactamase-producing amoxicillin/clavulanate-resistant with PBP3 mutations characterized as group III-like+. Relevant PBP3 mutations occurred in six strains without phenotypic piperacillin/tazobactam resistance. These mutations suggest a reduced efficacy of β-lactam antibiotics in these isolates.

Conclusions

Piperacillin/tazobactam resistance prevalence in invasive Hi is low in Germany. Reduced susceptibility was correlated with PBP3 mutations, in particular with group III mutations.

First global report about the prevalence of multi-drug resistant Haemophilus influenzae: a systematic review and meta-analysis

BACKGROUND

In recent decades, the prevalence of antibiotic resistance is increasing in Haemophilus influenzae (Haemophilus influenzae), which poses important challenges to global health. This research offers a comprehensive meta-analysis of the global epidemiology of multi-drug resistant (MDR) H. influenzae.

METHODS

In this study, we conducted a meta-analysis based on PRISMA checklist. Electronic databases including PubMed, ISI Web of Science, Scopus, EMBASE, and Google Scholar were reviewed using keywords related to H. influenzae and antibiotic resistance. Eligible studies were selected based on stringent inclusion and exclusion criteria. Then, data from these studies were analyzed using the Comprehensive Meta-Analysis (CMA) software.

RESULTS

Of 375 retrieved articles, 16 met the inclusion criteria. These studies were conducted from 2003 to 2023 and analyzed data from 19,787 clinical isolates of H. influenzae. The results showed different levels of resistance of H. influenzae to different antibiotics: ampicillin (36%), azithromycin (15.3%), ceftriaxone (1.4%), etc. The global prevalence for beta-lactamases producing H. influenzae and MDR H. influenzae was measured 34.9% and 23.1%, respectively. The prevalence rate of MDR H. influenzae was higher in Asian countries (24.6%) compared to Western regions (15.7%). MDR H. influenzae had the highest prevalence in meningitis cases (46.9%) and the lowest prevalence in acute otitis media (0.5%).

CONCLUSIONS

The prevalence of MDR H. influenzae has been increasing worldwide, especially in Asian regions. This highlights the urgent need for monitoring and implementation of effective antibiotic stewardship programs globally.

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.

Reliability of nasopharyngeal PCR for the detection of otopathogens in children with uncomplicated acute otitis media compared to culture

Otopathogens in acute otitis media (AOM) have implications for care because the likelihood of resolution without antibiotics and optimal antibiotic agent varies by microorganism. We aimed to determine the sensitivity, specificity, positive predictive value, and negative predictive value of nasopharyngeal (NP) qualitative polymerase chain reaction (PCR) for common bacterial otopathogens in children with AOM compared to NP culture. NP flocked swabs collected from enrolled children aged 6 to 35 months with uncomplicated AOM in Denver, CO were tested by culture and multiplex PCR. The sensitivity and negative predictive value of PCR using culture as a reference were high (H. influenzae 93.3%, 98.0%; S. pneumoniae 94.2%, 95.1%; M. catarrhalis 92.3%, 86.4%); whereas the specificity and positive predictive value were lower and varied by organism (54.2%-84.1%, 55.1%-69.2%, respectively). PCR detected 1.5 times more organisms than culture. NP PCR has a high predictive value for excluding otopathogens compared to culture and warrants exploration as a diagnostic tool.

Leveraging the human microbiota to target bacterial respiratory pathogens: new paths toward an expanded antimicrobial armamentarium

Acute respiratory infections are the most frequent infections across the lifespan and are the leading infectious cause of death among children globally. Bacterial respiratory infections are routinely treated with antibiotics, nearly all of which are derived from microbial natural products. Unfortunately, antibiotic-resistant bacteria are an increasingly frequent cause of respiratory infections, and there are few new antibiotics in development that target these pathogens. In the article by Stubbendieck et al., the authors identified Rothia species that demonstrate in vitro and ex vivo growth inhibition of the respiratory pathobiont Moraxella catarrhalis. The authors present experiments suggesting that this activity is mediated at least in part through the secretion of a novel peptidoglycan endopeptidase that targets the M. catarrhalis cell wall. In this commentary, we discuss these findings in the context of the urgent threat of antimicrobial resistance and highlight the promise of the human respiratory microbiota as a source of novel biotherapeutics.

Molecular characterization of multidrug-resistant non-typeable Haemophilus influenzae with high-level resistance to cefuroxime, levofloxacin, and trimethoprim-sulfamethoxazole

BACKGROUND

Non-typeable Haemophilus influenzae (NTHi) has become the major cause of invasive H. influenzae diseases in the post-H. influenzae type b vaccine era. The emergence of multidrug-resistant (MDR) NTHi is a growing public health problem. Herein, we investigated the molecular basis of MDR in NTHi. The isolated NTHi were subjected to antimicrobial susceptibility testing for 12 agents. Whole genome and plasmid sequencing were conducted and analyzed to identify significant genetic variations and plasmid-encoded genes conferred antibiotic resistance.

RESULTS

Thirteen (50%) MDR NTHi isolates were obtained; of these, 92.3% were non-susceptible to ampicillin, 30.8% to amoxicillin-clavulanate, 61.5% to cefuroxime, 61.5% to ciprofloxacin/levofloxacin, 92.3% to trimethoprim-sulfamethoxazole, 30.8% to tetracycline, and 7.7% to azithromycin. Eight ampicillin-resistant isolates were β-lactamase positive; of these, 6 carried bla_TEM-1 and 2 carried bla_ROB-1, whereas 4 were β-lactamase negative. Genetic variations in mrdA, mepA, and pbpG were correlated with amoxicillin-clavulanate non-susceptibility, whereas variations in ftsI and lpoA conferred cefuroxime resistance. Five variations in gyrA, 2 in gyrB, 3 in parC, 1 in parE, and 1 in the parC-parE intergenic region were associated with levofloxacin/ciprofloxacin non-susceptibility. Among these genes, 8 variations were linked to high-level levofloxacin resistance. Six variations in folA were associated with trimethoprim-sulfamethoxazole resistance. Plasmid-bearing tet(B) and mef(A) genes were responsible for tetracycline and azithromycin resistance in 4 and 1 MDR isolates, respectively.

CONCLUSIONS

This study clarified the molecular epidemiology of MDR in NTHi. This can benefit the monitoring of drug resistance trends in NTHi and the adequate medical management of patients with NTHi infection.

Characterization of Serotypes and Molecular Drug Resistance Patterns of Haemophilus influenzae in Kunming Children

The present study aimed to determine the capsular serotype distribution and antimicrobial drug resistance patterns of Haemophilus influenzae from children in the Kunming region of China. This information could guide policymakers in clinical treatment. In the present study, H. influenzae isolates were tested for their serotypes, antimicrobial susceptibility pattern, and presence of β-lactamases. One-hundred forty-eight H. influenzae strains isolated from children 0-2 years old were investigated for capsular types by glass slide agglutination and molecular methods, and biotyped by the biochemical reactions. The drug resistance-encoding genes TEM-1, ROB-1, and the ftsI gene mutations PBP3-3, and PBP3-BLN were detected with real-time quantitative polymerase chain reaction (qPCR). The prevalence of β-lactamase-producing strains (60.3%) was significantly higher (p < 0.05) than non-enzyme-producing strains. β-Lactamase-producing strains were multidrug resistant to various antibiotics such as ampicillin, tetracycline, sulfamethoxazole/trimethoprim, chloramphenicol, cefuroxime, and cefaclor. Among β-lactamase-producing strains, the detection rates of the TEM-1, PBP3-BLN, PBP3-s, and ROB-1 were 54.1%, 18.9%, 11.8%, and 6.9%, respectively. The biotyping results show that most H. influenzae strains were of type II and III. Non-typeable H. influenzae (NTHi) accounted for 89.3% of the strains. NTHi strains were the most prevalent in this region; most belonged to biological types II and III. β-Lactamase-positive ampi-cillin-resistant (BLPAR) strains were prevalent among H. influenzae isolates in this region.

New insights into the treatment of acute otitis media

INTRODUCTION

Acute otitis media (AOM) affects most (80%) children by 5 years of age and is the most common reason children are prescribed antibiotics. The epidemiology of AOM has changed considerably since the widespread use of pneumococcal conjugate vaccines, which has broad-reaching implications for management.

AREAS COVERED

In this narrative review, we cover the epidemiology of AOM, best practices for diagnosis and management, new diagnostic technology, effective stewardship interventions, and future directions of the field. Literature review was performed using PubMed and ClinicalTrials.gov.

EXPERT OPINION

Inaccurate diagnoses, unnecessary antibiotic use, and increasing antimicrobial resistance remain major challenges in AOM management. Fortunately, effective tools and interventions to improve diagnostic accuracy, de-implement unnecessary antibiotic use, and individualize care are on the horizon. Successful scaling of these tools and interventions will be critical to improving overall care for children.

Molecular Epidemiology and Antibiotic Resistance Analysis of Non-Typeable Haemophilus influenzae (NTHi) in Guangzhou: A Representative City of Southern China

This study aimed to investigate the molecular epidemiology and antibiotic resistance of Haemophilus influenzae in Guangzhou, China. A total of 80 H. influenzae isolates were collected from the First Affiliated Hospital of Guangzhou Medical University from January 2020 to April 2021. Species identification, antimicrobial susceptibility, molecular capsular typing, multilocus sequence typing and the clinical characteristics analysis of patients were performed. For all recruited isolates, the majority of H. influenzae strains from patients with respiratory symptoms were found to be non-typeable H. influenzae (NTHi). The isolates were relative susceptible to third- and fourth-generation cephalosporins, quinolones and chloramphenicol, despite having a high ampicillin resistance rate (>70%). The genotyping results reveal a total of 36 sequence types (STs), with ST12 being the most prevalent ST. Remarkably, the 36 STs identified from 80 NTHi isolates within a short period of 15 months and in a single medical setting have revealed a high genetic diversity in NTHi isolates. In comparison, it is noteworthy that the most prevalent STs found in the present study have rarely been found to overlap with those from previous studies. This is the first study on the molecular epidemiology of NTHi isolates in Guangzhou, a city that is representative of southern China.

Can non-typeable Haemophilus influenzae carriage surveillance data infer antimicrobial resistance associated with otitis media?

Importance

In remote communities of the Northern Territory, Australia, children experience high rates of otitis media (OM), commonly caused by non-typeable Haemophilus influenzae (NTHi). Few data exist on antibiotic susceptibility of NTHi from OM.

Objective

To determine whether population-level nasopharyngeal NTHi antibiotic susceptibility data could inform antibiotic treatment for OM.

Methods

NTHi isolates (n = 92) collected from ear discharge between 2003 and 2013 were selected to time- and age-match NTHi isolates from the nasopharyngeal carriage (n = 95). Antimicrobial susceptibility were tested. Phylogenomic trees and a genome-wide association study (GWAS) were performed to determine the similarity of nasopharyngeal and ear isolates at a population level.

Results

Among 174 NTHi isolates available for antimicrobial susceptibility testing, 10.3% (18/174) were resistant to ampicillin and 9.2% (16/174) were resistant to trimethoprim-sulfamethoxazole. Small numbers of isolates (≤3) were resistant to tetracycline, chloramphenicol, or amoxicillin-clavulanic acid. There was no statistical difference in the proportion of ampicillin-resistant (P = 0.11) or trimethoprim-sulfamethoxazole-resistant isolates (P = 0.70) between ear discharge and nasopharynx-derived NTHi isolates. Three multi-drug resistant NTHi isolates were identified. Phylogenomic trees showed no clustering of 187 Haemophilus influenzae isolates based on anatomical niche (nasopharynx or ear discharge), and no genetic variations that distinguished NTHi derived from ear discharge and nasopharyngeal carriage were evident in the GWAS.

Interpretation

In this population-level study, nasopharyngeal and ear discharge isolates did not represent distinct microbial populations. These results support tracking of population-level nasopharyngeal NTHi antibiotic resistance patterns to inform clinical management of OM in this population.

Reduction strategies for inpatient oral third-generation cephalosporins at a cancer center: An interrupted time-series analysis

Oral third-generation cephalosporins (3GCs) are not recommended for use owing to their low bioavailability and the risk of emergence of resistant microorganisms with overuse. A standardized and effective method for reducing their use is lacking. Here, in a 60-month, single-institution, interrupted time-series analysis, which was retrospectively conducted between April 1, 2017, and March 31, 2022, we evaluated the effectiveness of a four-phase intervention to reduce the use of 3GCs in patients at a cancer center: Phase 1 (pre-intervention), Phase 2 (review of clinical pathways), Phase 3 (establishment of infectious disease consultation service and implementation of antimicrobial stewardship program), and Phase 4 (educational lecture and pop-up displays for oral antimicrobials at the time of ordering). Although no significant changes were observed in Phases 3 and 4, the first intervention resulted in a significant decrease in the trend and level of days of therapy (DOT) for 3GCs. The level for cephalexin DOT and the trend for sulfamethoxazole-trimethoprim DOT increased in Phase 4, and the trend for amoxicillin and amoxicillin-clavulanate DOT increased in Phase 3. Macrolide DOT showed a decreasing trend in Phases 2 and 4 and decreasing and increased levels in Phases 3 and 4, respectively; no change was observed for quinolones. Actual and adjusted purchase costs of 3GCs decreased significantly during all study periods, while those for oral antimicrobials decreased in Phase 2, and actual purchase costs increased in Phases 3 and 4. No significant reduction in resistant organisms, length of hospital stay, or mortality was observed. This is the first study on the effects of oral 3GC reduction strategies in patients with cancer. We conclude that even facilities that substantially use antimicrobials can efficiently reduce the use of 3GCs.

Use of trans-complementation method to determine the effects of various ftsI mutations on β-lactamase-negative ampicillin-resistant (BLNAR) Haemophilus influenzae strains

Haemophilus influenzae is a causative agent of serious infections, especially among children. β-lactam antibiotics are commonly used for the treatment of these infections. Among H. influenzae isolates, β-lactam resistance is due to the presence of β-lactamase, or to mutations in the ftsI gene that generate altered PBP3 (penicillin-binding protein 3) with reduced affinity for β-lactams (BLNAR-β-lactamase-negative, ampicillin-resistant). Wild-type ftsI gene encoding for PBP3 was amplified in whole from β-lactam susceptible H. influenzae Rd and cloned in pLS88 plasmid to obtain pADUTAS17, which was then used to transform known BLNAR strains, susceptible strains, and a strain (CF55) with wild-type ftsI but unexplained reduced β-lactam susceptibility. Ampicillin and cefotaxime MICs (minimum inhibitory concentration) were determined after transformation with pLS88 and pADUTAS17 plasmids. The results showed that antibiotic susceptibilities were not affected by trans-complementation for isolates carrying wild-type ftsI gene. However, trans-complementation for all BLNAR strains showed decreases between - 0.957 and 0.5-fold for ampicillin and cefotaxime, confirming the role of the PBP3 substitutions in the BLNAR phenotype of these isolates. The first article showed that trans-complementation might be a useful tool in the investigation of decreased β-lactam susceptibility in H. influenzae.

Molecular epidemiology and antimicrobial resistance of Haemophilus influenzae in Guiyang, Guizhou, China

Background

The widespread use of antimicrobials and Haemophilus influenzae type b (Hib) vaccine worldwide has altered the epidemiological patterns of invasive H. influenzae. Nonetheless, little is currently known on the epidemiological characteristics of H. influenzae in Guiyang, Guizhou, China.

Objective

To determine the serotype distribution, antimicrobial resistance and Multilocus Sequence Typing (MLST) of H. influenzae in hospitalized patients in Guiyang City.

Methods

A total of 196 clinical isolates from hospitalized patients were collected. Serotypes were determined according to the specific capsule gene, bexA, amplified by PCR. According to the guidelines of Clinical and Laboratory Standards Institute (CLSI) 2020 drug susceptibility tested, and the results determined. The chromogenic cephalosporin nitrocefin method was used to detect β-lactamase production, β-lactamase negative, ampicillin-resistant (BLNAR) strains were detected by PCR amplification and sequencing of the penicillin-binding protein 3 (PBP3) locus of ftsI. Multilocus Sequence Typing was performed for molecular typing.

Results

All isolates studied were non-typeable H. influenzae (NTHi). Most patients originated from the pediatrics department (78.6%, 154/196), and suffered from lung with respiratory tract infection (pneumonia and bronchitis, 68.4%, 134/196). The resistance rates of ampicillin, cefaclor and azithromycin were 71.4% (140/196), 36.7% (72/196) and 34.2% (67/196), respectively. 40.3% (79/196) of strains were β-lactamase positive ampicillin-resistant (BLPAR). All BLPAR carried the TEM-1 gene. 9.2% (18/196) were β-lactamase negative ampicillin-resistant strains (BLNAR). The PBP3 mutation was detected in the ampicillin-resistant strains (n = 113), of which 18 belonged to group IIa. A total of 49 sequence types (ST) and 23 clonal complexes (CC) were detected, among which CC107 (ST107, n = 27; ST1002, n = 5; ST1218, n = 5) was the most frequent clonal complexes. BLPAR isolates mostly belonged to ST107 (20/79), while BLNAR was predominantly distributed in ST12 (5/18).

Conclusion

H. influenzae infections are predominately caused by genetically diverse NTHi among hospitalized patients in Guiyang. The prevalence of β-lactamase production and PBP3 mutation may contribute to the high local ampicillin resistance rate.

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

BACKGROUND

Quinolone-resistant bacteria are known to emerge via the accumulation of mutations in a stepwise manner. Recent studies reported the emergence of quinolone low-susceptible Haemophilus influenzae ST422 isolates harbouring two relevant mutations, although ST422 isolates harbouring one mutation were never identified.

OBJECTIVES

To investigate if GyrA and ParC from quinolone low-susceptible isolates can be transferred horizontally and simultaneously to susceptible isolates.

METHODS

Genomic DNA was extracted from an H. influenzae isolate harbouring amino acid substitutions in both gyrA and parC and mixed with clinical isolates. The emergence of resistant isolates was compared, and WGS analysis was performed.

RESULTS

By adding the genomic DNA harbouring both mutated gyrA and parC, resistant bacteria exhibiting recombination at gyrA only or both gyrA and parC loci were obtained on nalidixic acid and pipemidic acid plates, and the frequency was found to increase with the amount of DNA. Recombination events in gyrA only and in both gyrA and parC occurred with at least 1 and 1-100 ng of DNA, respectively. The genome sequence of a representative strain showed recombination events throughout the genome. The MIC of quinolone for the resulting strains was found to be similar to that of the donor. Although the recombination efficacy was different among the various strains, all strains used in this study obtained multiple genes simultaneously.

CONCLUSIONS

These findings indicate that H. influenzae can simultaneously obtain more than two mutated genes. This mechanism of horizontal transfer could be an alternative pathway for attaining quinolone resistance.

Non-typeable Haemophilus influenza ventriculitis, a case report and literature review

Introduction

and importance: Haemophilus influenza severe presentations have decreased dramatically after the Hib vaccination was introduced. However, due to the emergence of Multi-drug resistance organisms, severe presentations like meningitis and ventriculitis may occur.

Case presentation

Here, we have described a rarely reported case of non-typeable Haemophilus influenza ventriculitis in a previously healthy patient. MRI of the head with contrast was suggestive of tiny foci of diffusion restriction in occipital horns of bilateral ventricles with minimal intraventricular pus formation. The diagnosis was confirmed based on blood culture results and MRI findings as the patient refused to have a lumbar puncture procedure for CSF analysis. The patient was treated with intravenous antibiotics and showed a good response.

Clinical discussion

In the post-HiB immunization era, we have seen a decline in invasive diseases caused by Type B Haemophilus influenza. However, non-typeable Haemophilus influenzae is now on the rise. Central nervous system infection due to non-typable Haemophilus influenza is infrequent as this organism is predominantly a respiratory mucosal pathogen resulting in acute and chronic respiratory tract infections. Multi-drug resistance of non-typeable Haemophilus influenzae is also becoming a cause of concern.

Conclusion

Ventriculitis secondary to non-typeable beta-lactamase non-producing, ampicillin-resistant (BLNAR) Haemophilus influenza is rare, and more such cases need to be reported within the adult population to avoid under-recognition.

Pharmaceutical nanotechnology: Antimicrobial peptides as potential new drugs against WHO list of critical, high, and medium priority bacteria

Nanobiotechnology is a relatively unexplored area that has, nevertheless, shown relevant results in the fight against some diseases. Antimicrobial peptides (AMPs) are biomacromolecules with potential activity against multi/extensively drug-resistant bacteria, with a lower risk of generating bacterial resistance. They can be considered an excellent biotechnological alternative to conventional drugs. However, the application of several AMPs to biological systems is hampered by their poor stability and lifetime, inactivating them completely. Therefore, nanotechnology plays an important role in the development of new AMP-based drugs, protecting and carrying the bioactive to the target. This is the first review article on the different reported nanosystems using AMPs against bacteria listed on the WHO priority list. The current shortage of information implies a nanobiotechnological potential to obtain new drugs or repurpose drugs based on the AMP-drug synergistic effect.

Antimicrobial resistance among Haemophilus influenzae isolates responsible for lower respiratory tract infections in Poland, 2005-2019

Haemophilus influenzae is a human-specific pathogen responsible for respiratory tract infections, meningitis, and sepsis. The study aimed to characterize antibiotic resistance in H. influenzae strains isolated from patients with lower respiratory tract infections over 15 years in Poland. The minimum inhibitory concentrations (MICs) of clinically relevant antibiotics were determined by broth microdilution method. Screening for beta-lactam resistance was performed in all isolates following EUCAST recommendation. Finally, relevant changes in penicillin-binding protein 3 (PBP3) were detected by PCR screening. Of the 1481 isolates collected between 2005 and 2019, 12.6%, 0.2%, 17.1%, and 0.2% were resistant to ampicillin, amoxicillin/clavulanate, cefuroxime, and ceftriaxone, respectively. Among them, 74.4% (1102/1481) of isolates were categorized as BLNAS (β-lactamase negative, ampicillin-susceptible), 13.0% (192/1481) as BLNAS with modified PBP3 (mutations in ftsI gene), 2.6% (39/1481) as BLNAR (β-lactamase negative, ampicillin-resistant), and 0.2% had PBP3 modifications typical for high-BLNAR. Production of β-lactamase characterized 9.7% of isolates (8.6% BLPAR-β-lactamase-positive, ampicillin-resistant, and 1.1% BLPACR-β-lactamase-positive, amoxicillin-clavulanate resistant). Three isolates with PBP3 modifications typical for high-BLNAR proved resistant to ceftriaxone (MIC > 0.125 mg/L). Resistance to ciprofloxacin, chloramphenicol, tetracycline, and trimethoprim-sulfamethoxazole was observed in 0.1%, 0.5%, 1.6%, and 24.7% of isolates, respectively. This is the first report of Polish H. influenzae isolates resistant to third-generation cephalosporins. Polish H. influenzae isolates demonstrate similar susceptibility trends as in many other countries. The substantial proportion of β-lactam-resistant isolates and the emergence of those resistant to third-generation cephalosporins are of great concern and should be under surveillance.

Serotype Distribution and Antimicrobial Resistance Profile of Haemophilus influenzae Isolated from School Children with Acute Otitis Media

Haemophilus influenzae is a Gram-negative opportunistic bacterial pathogen of the human respiratory tract. This study describes the prevalence, serotype distribution, and susceptibility profiles of H. influenzae strains isolated from the nasopharynx of school children with acute otitis media (AOM) in Banyumas Regency, Central Java, Indonesia. H. influenzae was isolated from nasopharyngeal swab specimens using chocolate agar plates supplemented with IsoVitaleX and bacitracin. Serotyping was performed using quantitative polymerase chain reaction. Antimicrobial susceptibility profiles were determined using a microdilution broth assay. H. influenzae was present in 69.7% of samples (85/122). Nontypeable H. influenzae (NHTi) was the most common serotype (95.3%), followed by H. influenzae type b (3.5%) and H. influenzae type f (1.2%). All the H. influenzae isolates were susceptible to levofloxacin, ceftriaxone, imipenem, meropenem, cefuroxime, and cefixime. Most isolates were susceptible to sparfloxacin (99%), cefepime (99%), amoxicillin/clavulanic acid 2 : 1 (99%), ampicillin/sulbactam 2 : 1 (96%), chloramphenicol (94%), tetracycline (93%), ampicillin (87%), and clarithromycin (82%). Nineteen percent of the isolates were resistant to cotrimoxazole, and 11% of the isolates were resistant to ampicillin. This study showed that H. influenzae carriage among samples was dominated by NTHi and less susceptible to cotrimoxazole.

High-Level Quinolone-Resistant Haemophilus haemolyticus in Pediatric Patient with No History of Quinolone Exposure

The prevalence of antimicrobial resistance among Haemophilus spp. is a critical concern, but high-level quinolone-resistant strains had not been isolated from children. We isolated high-level quinolone-resistant H. haemolyticus from the suction sputum of a 9-year-old patient. The patient had received home medical care with mechanical ventilation for 2 years and had not been exposed to any quinolones for >3 years. The H. haemolyticus strain we isolated, 2019-19, shared biochemical features with H. influenzae. However, whole-genome analysis found this strain was closer to H. haemolyticus. Phylogenetic and mass spectrometry analyses indicated that strain 2019-19 was in the same cluster as H. haemolyticus. Comparison of quinolone resistance-determining regions showed strain 2019-19 possessed various amino acid substitutions, including those associated with quinolone resistance. This report highlights the existence of high-level quinolone-resistant Haemophilus species that have been isolated from both adults and children.

Quinolone resistance is transferred horizontally via uptake signal sequence recognition in Haemophilus influenzae

The presence of Haemophilus influenzae strains with low susceptibility to quinolones has been reported worldwide. However, the emergence and dissemination mechanisms remain unclear. In this study, a total of 14 quinolone-low-susceptible H. influenzae isolates were investigated phylogenetically and in vitro resistance transfer assay in order to elucidate the emergence and dissemination mechanisms. The phylogenetic analysis based on gyrA sequences showed that strains with the same sequence type determined by multilocus sequence typing were classified into different clusters, suggesting that H. influenzae quinolone resistance emerges not only by point mutation, but also by the horizontal transfer of mutated gyrA. Moreover, the in vitro resistance transfer assay confirmed the horizontal transfer of quinolone resistance and indicated an active role of extracellular DNA in the resistance transfer. Interestingly, the horizontal transfer of parC only occurred in those cells that harbored a GyrA with amino acid substitutions, suggesting a possible mechanism of quinolone resistance in clinical settings. Moreover, the uptake signal and uptake-signal-like sequences located downstream of the quinolone resistant-determining regions of gyrA and parC, respectively, contributed to the horizontal transfer of resistance in H. influenzae. Our study demonstrates that the quinolone resistance of H. influenzae could emerge due to the horizontal transfer of gyrA and parC via recognition of an uptake signal sequence or uptake-signal-like sequence. Since the presence of quinolone-low-susceptible H. influenzae with amino acid substitutions in GyrA have been increasing in recent years, it is necessary to focus our attention to the acquisition of further drug resistance in these isolates.

The effects of the dietary compound L-sulforaphane against respiratory pathogens

L-sulforaphane (LSF) is an isothiocyanate derived from cruciferous vegetables that has long been known for its anticarcinogenic, antioxidant and anti-inflammatory effects. LSF also possesses antimicrobial properties, although the evidence for this is limited. Respiratory pathogens, such as Streptococcus pneumoniae, Haemophilus influenzae, Streptococcus pyogenes and respiratory syncytial virus (RSV), are leading global causes of illness and death among children aged under five years, particularly in resource-poor countries where access to vaccines are limited or, in the case of S. pyogenes and RSV, vaccines have not been licensed for use in humans. Therefore, alternative strategies to prevent and/or treat these common infectious diseases are urgently needed. This study was conducted to investigate the antimicrobial effects of LSF against common respiratory pathogens, S. pneumoniae (serotypes 1 and 6B), H. influenzae type B (HiB), non-typeable H. influenzae (NTHi), S. pyogenes and RSV in relevant human cell-based models. LSF significantly inhibited the growth of H. influenzae, but not S. pneumoniae or S. pyogenes. LSF did not improve opsonophagocytic capacity or killing by human phagocytic cell lines (HL-60s and THP-1 macrophages) for S. pneumoniae yet showed some improved killing for H. influenzae species in THP-1 macrophages. However, LSF significantly reduced RSV infection in human lung epithelial cells, associated with increased expression of cyclin D1 (CCND1) gene as well as the antioxidant genes, nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase 1 (HMOX-1). Overall, LSF represents an exciting avenue for further antimicrobial research, particularly as a novel therapy against H. influenzae species and RSV.

Antimicrobial resistance of Haemophilus influenzae isolates from pediatric hospitals in Mainland China: Report from the ISPED program, 2017-2019

PURPOSE

This study set out to determine the antimicrobial resistance trends of Haemophilus influenzae isolates from pediatric hospitals in Mainland China, which would provide basis for clinical treatment.

METHODS

The Infectious Disease Surveillance of Pediatrics (ISPED) collaboration group conducted this study. H. influenzae strains isolated from nine pediatric hospitals in Mainland China were included. Disk diffusion method was used for antimicrobial susceptibility test. Cefinase disc was used for detection of β-lactamase.

RESULTS

In total, 13810 H. influenzae isolates were included during 2017-2019: 93.17% of which were from respiratory tract specimens, 4.63% from vaginal swabs, 1.10% from secretion, and 1.10% from others. Of all strains, 63.32% isolates produced β-lactamase; 8.22% isolates were β-lactamase-negative and ampicillin-resistant (BLNAR). The resistance to sulfamethoxazole-trimethoprim was 70.98%, followed by resistance to ampicillin (69.37%), cefuroxime (51.35%), ampicillin-sulbactam (38.82%), azithromycin (38.21%), amoxicillin-clavulanate (35.28%). More than 90% of H. influenzae isolates were susceptible to ceftriaxone, cefotaxime, meropenem, levofloxacin and chloramphenicol. The resistance rate of ampicillin and azithromycin in H. influenzae showed an increasing trend through the years. Statistically significant differences in antibiotic-resistance rates of all the antibiotics except chloramphenicol were found in different regions. The major Multi-Drug Resistance pattern was resistant to β-lactams, macrolides, and sulfonamides.

CONCLUSIONS

There is a rising trend of resistance rate of ampicillin and azithromycin in H. influenzae. Antimicrobial resistance of H. influenzae deserves our ongoing attention. Third-generation cephalosporin could be the preferred treatment option of infections caused by ampicillin-resistant H. influenzae.

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.

Particulate air pollution and respiratory Haemophilus influenzae infection in Mianyang, southwest China

Particulate air pollution is correlated with many respiratory diseases. However, few studies have focused on the relationship between air particulate exposure and respiratory Heamophilus influenzae infection. Therefore, we detected respiratory Heamophilus influenzae infection by bacterial culture of sputum of patients, and we collected particulate air pollution data (including PM2.5 and PM10) from a national real-time urban air quality platform to analyze the relationship between particulate air pollution and respiratory Heamophilus influenzae infection. The mean concentrations of PM2.5 and PM10 were 37.58 μg/m3 and 58.44 μg/m3, respectively, showing particulate air pollution remains a severe issue in Mianyang. A total of 828 strains of Heamophilus influenzae were detected in sputum by bacterial culture. Multiple correspondence analysis suggested the heaviest particulate air pollution and the highest Heamophilus influenzae infection rates were all in winter, while the lowest particulate air pollution and the lowest Heamophilus influenzae infection rates were all in summer. In a single-pollutant model, each elevation of 10 μg/m3 of PM2.5, PM10, and PM2.5/10 (combined exposure level) increased the risk of respiratory Heamophilus influenzae infection by 34%, 23%, and 29%, respectively. Additionally, in the multiple-pollutant model, only PM2.5 was significantly associated with respiratory Heamophilus influenzae infection (B, 0.46; 95% confidence interval, 0.05-0.87), showing PM2.5 is an independent risk factor for respiratory Heamophilus influenzae infection. In summary, this study highlights air particulate exposure could increase the risk of respiratory Heamophilus influenzae infection, implying that stronger measures need to be taken to protect against respiratory infection induced by particulate air pollution.

Dissemination of quinolone low-susceptible Haemophilus influenzae ST422 in Tokyo, Japan

INTRODUCTION

Haemophilus influenzae with a reduced susceptibility to quinolones (quinolone low-susceptible H. influenzae) has recently emerged in Japan. In addition, the regional outbreak of the quinolone low-susceptible H. influenzae ST422 clone has been reported. In this study, we isolated this clone from an acute care hospital located in a geographically different area from the previous outbreak and characterised the nature of this clone.

METHODS

Eighty-nine H. influenzae isolated between 2017 and 2019 were tested. The antimicrobial susceptibility was determined by the broth dilution method. The genetic background was analysed by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing. Growth ability and β-lactamase acquisition were evaluated by growth curve analysis and conjugative transfer experiments, respectively.

RESULTS

Quinolone low-susceptible isolates accounted for 4.2% (1/24) in 2018 and 13.9% (5/36) in 2019. Most of the quinolone low-susceptible strains (83.3%) were classified as ST422 and had amino acid substitutions in quinolone resistance-determining regions in both GyrA and ParC. The patients' backgrounds were highly diverse. In addition, these isolates showed the same PFGE pattern as outbreak strains. The growth of ST422 clone was relatively faster than other clones. Furthermore, ST422 clone was able to acquire β-lactamase from a β-lactamase positive strain by horizontal transfer, becoming highly resistant to β-lactams.

CONCLUSION

Our study indicated that the quinolone low-susceptible H. influenzae ST422 clone has been spreading in the community undetected. In addition, this clone has the potential to grow faster and become more resistant through exogenous gene transfer. Therefore, ST422 clone should be monitored attention throughout Japan.

Early detection of drug-resistant Streptococcus pneumoniae and Haemophilus influenzae by quantitative flow cytometry

Early detection of drug resistance contributes to combating drug-resistant bacteria and improving patient outcomes. Microbial testing in the laboratory is essential for treating infectious diseases because it can provide critical information related to identifying pathogenic bacteria and their resistance profiles. Despite these clinical requirements, conventional phenotypic testing is time-consuming. Additionally, recent rapid drug resistance tests are not compatible with fastidious bacteria such as Streptococcus and Haemophilus species. In this study, we validated the feasibility of direct bacteria counting using highly sensitive quantitative flow cytometry. Furthermore, by combining flow cytometry and a nucleic acid intercalator, we constructed a highly sensitive method for counting viable fastidious bacteria. These are inherently difficult to measure due to interfering substances from nutrients contained in the medium. Based on the conventional broth microdilution method, our method acquired a few microliter samples in a time series from the same microplate well to exclude the growth curve inconsistency between the samples. Fluorescent staining and flow cytometry measurements were completed within 10 min. Therefore, this approach enabled us to determine antimicrobial resistance for these bacteria within a few hours. Highly sensitive quantitative flow cytometry presents a novel avenue for conducting rapid antimicrobial susceptibility tests.