Emergence and Inter- and Intrahost Evolution of Pandrug-Resistant Klebsiella pneumoniae Coharboring tmexCD1-toprJ1, blaNDM-1, and blaKPC-2

Emergence of two novel tmexCD-toprJ subtypes mediating tigecycline resistance in the megaplasmids from Pseudomonas putida

The widespread antimicrobial resistance (AMR) problem poses a serious health threat, leaving few drug choices, including tigecycline, to treat multidrug resistance pathogens. However, a plasmid-borne tigecycline resistance gene cluster, tmexCD1-toprJ1, emerged and conferred tigecycline resistance. In this study, we identified two novel subtypes, tmexCD2.3-toprJ2.3 and tmexCD2.4-toprJ1b, obtained from three chicken-origin Pseudomonas putida isolates. Two types of megaplasmids were found as the vital vehicle of these tmexCD-toprJ variants. Phylogenetic and genomic analysis indicated the two variants were mainly distributed in Pseudomonas and acted as an evolved intermediated state precursor of tmexCD2-toprJ2. Further gene cloning assay revealed both the expression of tmexCD2.3-toprJ2.3 and tmexCD2.4-toprJ1b could confer multiple antimicrobial resistance, mediating 8- to 16-fold increase of tigecycline MIC. Importantly, two key nucleotide differences in promoter region influence the promoter activity between PtmexC2.3 and PtmexC2.4, while the downregulation effect of TNfxB on the transcriptional expression level of tmexCD2.3-toprJ2.3 and tmexCD2.4-toprJ1b were observed. The emergency of two novel tmexCD-toprJ variants necessitates preventive measures to curb their spread and highlights concerns about more emerging tmexCD-toprJ variants.

Antibiotic heteroresistance in Klebsiella pneumoniae: Definition, detection methods, mechanisms, and combination therapy

Klebsiella pneumoniae is a common opportunistic pathogen that presents significant challenges in the treatment of infections due to its resistance to multiple antibiotics. In recent years, K. pneumoniae has been reported for the development of heteroresistance, a phenomenon where subpopulations of the susceptible bacteria exhibit resistance. This heteroresistance has been associated with increased morbidity and mortality rates. Complicating matters further, its definition and detection pose challenges, often leading to its oversight or misdiagnosis. Various mechanisms contribute to the development of heteroresistance in K. pneumoniae, and these mechanisms differ among different antibiotics. Even for the same antibiotic, multiple mechanisms may be involved. However, our current understanding of these mechanisms remains incomplete, and further research is needed to gain a more comprehensive understanding of heteroresistance. While the clinical recommendation is to use combination antibiotic therapy to mitigate heteroresistance, this approach also comes with several drawbacks and potential adverse effects. In this review, we discuss the definition, detection methods, molecular mechanisms, and treatment of heterogenic resistance, aiming to pave the way for more effective treatment and management in the future. However, addressing the problem of heteroresistance in K. pneumoniae represents a long and complex journey that necessitates comprehensive research efforts.

A novel KPC-166 in ceftazidime/avibactam resistant ST307 Klebsiella pneumoniae causing an outbreak in intensive care COVID Unit, Italy

INTRODUCTION

Aim of the study was the molecular characterization of 21 ceftazidime/avibactam resistant (CZA-R) Klebsiella pneumoniae strains, collected in the period October 2021-March 2022 from an Intensive Care COVID Unit in a Northern Italian Hospital.

METHODS

After growth on selective/chromogenic culture media and susceptibility tests assessment, resistance genes content was ascertained for all the isolates by the HybriSpot 12 multiplexing, PCR and Whole-Genome Sequencing (WGS). Clonality was assessed by PFGE and MLST according to the Pasteur scheme. A SNPs-based phylogenetic tree was obtained comparing representative isolates and global genomes. The blaKPC gene horizontal transmission was evaluated by conjugation experiments. blaKPC-166 was cloned in a pCR2.1 vector and transformed in chemically competent TOP10 cells.

RESULTS

Sixteen inpatients resulted positive for colonization and/or infection by KPC-producing K. pneumoniae (KPC-Kp) strains. The 21 CZA-R KPC-Kp isolates obtained showed MDR phenotype; susceptibility to meropenem was always retained. All the CZA-R KPC-Kp presented a novel blaKPC variant, named blaKPC-166, showing a single nucleotide substitution (T811C) compared to the blaKPC-94; but related to blaKPC-2.

TWO DIFFERENT PULSOTYPES WERE DETECTED

A in 18/21 and B in 1/21 cases, two strains from the same patient being untypable by PFGE. Interestingly, the outbreak was sustained by the high-risk clone ST307, although the ST22, ST6342, ST6418 and ST6811 have also been identified and associated to KPC-166. Worryingly, blaKPC-166 could be transferred horizontally and, after cloning, it conferred resistance to CZA.

DISCUSSION

This novel variant confers CZA-resistance and carbapenems susceptibility restoration. As KPC-166 was found expressed by multiple Kp clones, greater efforts should be made to prevent the further dissemination of such strains in Italian clinical settings.

ST218 Klebsiella pneumoniae became a high-risk clone for multidrug resistance and hypervirulence

BACKGROUND

The occurrence of multidrug-resistant and hypervirulent Klebsiella pneumoniae (MDR-hvKp) worldwide poses a great challenge for public health. Few studies have focused on ST218 MDR-hvKp.

METHODS

Retrospective genomic surveillance was conducted at the Peking University Third Hospital from 2017 and clinical information was obtained. To understand genomic and microbiological characteristics, antimicrobial susceptibility testing, plasmid conjugation and stability, biofilm formation, serum killing, growth curves and whole-genome sequencing were performed. We also assessed the clinical and microbiological characteristics of ST218 compared with ST23.

RESULTS

A total of eleven ST218 Kp isolates were included. The most common infection type was lower respiratory tract infection (72.7%, 8/11) in our hospital, whereas ST23 hvKp (72.7%, 8/11) was closely associated with bloodstream infection. Notably, nosocomial infections caused by ST218 (54.5%, 6/11) was slightly higher than ST23 (36.4%, 4/11). All of the ST218 and ST23 strains presented with the virulence genes combination of iucA + iroB + peg344 + rmpA + rmpA2. Interestingly, the virulence score of ST218 was lower than ST23, whereas one ST218 strain (pPEKP3107) exhibited resistance to carbapenems, cephalosporins, β-lactamase/inhibitors and quinolones and harbored an ~ 59-kb IncN type MDR plasmid carrying resistance genes including blaNDM-1, dfrA14 and qnrS1. Importantly, blaNDM-1 and qnrS1 were flanked with IS26 located within the plasmid that could successfully transfer into E. coli J53. Additionally, PEKP2044 harbored an ~ 41-kb resistance plasmid located within tetA indicating resistance to doxycycline.

CONCLUSION

The emergence of blaNDM-1 revealed that there is great potential for ST218 Kp to become a high-risk clone for MDR-hvKp, indicating the urgent need for enhanced genomic surveillance.

Convergence of plasmid-mediated Colistin and Tigecycline resistance in Klebsiella pneumoniae

Objective

The co-occurrence of colistin and tigecycline resistance genes in Klebsiella pneumoniae poses a serious public health problem. This study aimed to characterize a K. pneumoniae strain, K82, co-harboring a colistin resistance gene (CoRG) and tigecycline resistance gene (TRG), and, importantly, investigate the genetic characteristics of the plasmid with CoRG or TRG in GenBank.

Methods

K. pneumoniae strain K82 was subjected to antimicrobial susceptibility testing, conjugation assay, and whole-genome sequencing (WGS). In addition, comparative genomic analysis of CoRG or TRG-harboring plasmids from K82 and GenBank was conducted. K. pneumoniae strain K82 was resistant to all the tested antimicrobials including colistin and tigecycline, except for carbapenems.

Results

WGS and bioinformatic analysis showed that K82 belonged to the ST656 sequence type and carried multiple drug resistance genes, including mcr-1 and tmexCD1-toprJ1, which located on IncFIA/IncHI2/IncHI2A/IncN/IncR-type plasmid pK82-mcr-1 and IncFIB/IncFII-type plasmid pK82-tmexCD-toprJ, respectively. The pK82-mcr-1 plasmid was capable of conjugation. Analysis of the CoRG/TRG-harboring plasmid showed that mcr-8 and tmexCD1-toprJ1 were the most common CoRG and TRG of Klebsiella spp., respectively. These TRG/CoRG-harboring plasmids could be divided into two categories based on mash distance. Moreover, we found an IncFIB/IncHI1B-type plasmid, pSYCC1_tmex_287k, co-harboring mcr-1 and tmexCD1-toprJ1. To the best of our knowledge, this is the first report on the co-occurrence of mcr-1 and tmexCD1-toprJ1 on a single plasmid.

Conclusion

Our research expands the known diversity of CoRG and TRG-harboring plasmids in K. pneumoniae. Effective surveillance should be implemented to assess the prevalence of co-harboring CoRG and TRG in a single K. pneumoniae isolate or even a single plasmid.