A Sequence Type 23 Hypervirulent Klebsiella pneumoniae Strain Presenting Carbapenem Resistance by Acquiring an IncP1 bla KPC-2 Plasmid

Early detection of OXA-232-producing Klebsiella pneumoniae in China predating its global emergence

Antibiotic resistance is a global health issue, with Klebsiella pneumoniae (KP) posing a particular threat due to its ability to acquire resistance to multiple drug classes rapidly. OXA-232 is a carbapenemase that confers resistance to carbapenems, a class of antibiotics often used as a last resort for treating severe bacterial infections. The study reports the earliest known identification of six OXA-232-producing KP strains that were isolated in Zhejiang, China, in 2008 and 2009 within a hospital, two years prior to the first reported identification of OXA-232 in France. The four KP strains carry the OXA-232 gene and exhibit hypervirulent loci, suggesting a broader temporal and geographical spread and integration of this resistance and virulence than previously recognized with implications for public health. Global analysis of all OXA-232-bearing KP strains revealed that OXA-232-encoding plasmids are conservative, while the strains were very diverse suggesting the plasmid mediated transmission of this carbapenemase genes. Importantly, a large proportion of the OXA-232-bearing KP strains also carried virulence plasmids, in particular the recent emergence of ST15 type of KP that carried both OXA-232-encoding plasmids and hypervirulent (hv) plasmids in China since 2019, highlighting the importance of the emergence of this type of KP strains in clinical setting. The early detection and investigations of OXA-232 in these strains warrants the retrospective studies to uncover the true timeline of antibiotic resistance spread, which could provide valuable insights for shaping future strategies to tackle the global health crisis.

In vitro activity of ceftazidime-avibactam, imipenem-relebactam, aztreonam-avibactam, and comparators toward carbapenem-resistant and hypervirulent Klebsiella pneumoniae isolates

IMPORTANCE

To our knowledge, this is the first study to report the in vitro activity of two novel antimicrobial drugs, including imipenem-relebactam (IMR) and aztreonam-avibactam (AZA), toward carbapenem-resistant and hypervirulent Klebsiella pneumoniae (CR-hvKP) strains. Our in vitro activity study revealed that only few antibacterial agents (including several novel agents) exhibit high antimicrobial activity toward carbapenem-resistant Klebsiella pneumoniae (CRKP) and CR-hvKP isolates. IMR and AZA may be promising therapeutic agents for the treatment of infections caused by CRKP and CR-hvKP isolates.

Involvement of Tn3 transposon in formation and transmission of hypervirulent and carbapenem-resistant Klebsiella pneumoniae

IMPORTANCE

Carbapenem-resistant Klebsiella pneumoniae (CRKP) is resistant to most common antibiotics, becoming the most important and prevalent nosocomial opportunity pathogen. Besides, K. pneumoniae can also cause severe community-acquired infections, such as primary liver abscess and endophthalmitis. These pathogens are commonly referred to as hvKp. CRKP and hvKp have evolved separately, each occupying its own clonal lineage and exhibiting a variety of properties. Our study provides important insights into the evolutionary events related to the arousal of virulence and drug resistance in K. pneumoniae through plasmid transmission, mediated by Tn3 transposon. Our study also provides evidence that multiple mechanisms contribute to the successful transfer of non-conjugative virulence plasmid, and the involvement of transposons enhances the efficiency. A good knowledge of its transmission mechanisms is fundamental to finding effective strategies to combat these threatening pathogens. Transposons are widely present in bacteria, spreading resistance and virulence genes between the environment and humans. Therefore, emerging transposon-mediated hypervirulent and carbapenem-resistant pathogens should be highly valued.

"Superbugs" with hypervirulence and carbapenem resistance in Klebsiella pneumoniae: the rise of such emerging nosocomial pathogens in China

Although hypervirulent Klebsiella pneumoniae (hvKP) can produce community-acquired infections that are fatal in young and adult hosts, such as pyogenic liver abscess, endophthalmitis, and meningitis, it has historically been susceptible to antibiotics. Carbapenem-resistant K. pneumoniae (CRKP) is usually associated with urinary tract infections acquired in hospitals, pneumonia, septicemias, and soft tissue infections. Outbreaks and quick spread of CRKP in hospitals have become a major challenge in public health due to the lack of effective antibacterial treatments. In the early stages of K. pneumoniae development, HvKP and CRKP first appear as distinct routes. However, the lines dividing the two pathotypes are vanishing currently, and the advent of carbapenem-resistant hypervirulent K. pneumoniae (CR-hvKP) is devastating as it is simultaneously multidrug-resistant, hypervirulent, and highly transmissible. Most CR-hvKP cases have been reported in Asian clinical settings, particularly in China. Typically, CR-hvKP develops when hvKP or CRKP acquires plasmids that carry either the carbapenem-resistance gene or the virulence gene. Alternatively, classic K. pneumoniae (cKP) may acquire a hybrid plasmid carrying both genes. In this review, we provide an overview of the key antimicrobial resistance mechanisms, virulence factors, clinical presentations, and outcomes associated with CR-hvKP infection. Additionally, we discuss the possible evolutionary processes and prevalence of CR-hvKP in China. Given the wide occurrence of CR-hvKP, continued surveillance and control measures of such organisms should be assigned a higher priority.

Characterization of ST11 and ST15 Carbapenem-Resistant Hypervirulent Klebsiella pneumoniae from Patients with Ventilator-Associated Pneumonia

Background

The prevalence of carbapenem-resistant hypervirulent Klebsiella pneumoniae (hv-CRKP) is a serious public threat globally. Here, we performed clinical, molecular, and phenotypic monitoring of hv-CRKP strains isolated from the intensive care unit (ICU) to offer evidence for prevention and control in hospitals.

Methods

Data analysis of ICU patients suffering from ventilator-associated pneumonia (VAP) because of hv-CRKP infection, admitted at the Chinese Teaching Hospital between March 2019 and September 2021 was performed. Patients' antibiotic-resistance genes, virulence-associated genes, and capsular serotypes of these isolates were detected. Homology analysis of the strains was performed by MLST and PFGE. Six different strains were tested for their virulence traits using the serum killing test and the Galleria mellonella infection assay. For whole genome sequencing, KP3 was selected as a representative strain.

Results

Clinical data of 19 hv-CRKP-VAP patients were collected and their hv-CRKP were isolated, including 10 of ST11-KL64, 4 of ST15-KL112, 2 of ST11-KL47, 1 of ST15-KL19, 1 of ST17-KL140, and 1 of ST48-KL62. Four ST15 and 8 ST11 isolates revealed high homology, respectively. Most strains carried the carbapenemase gene blaKPC-2 (14/19, 73.68%), followed by blaOXA-232 (4/19, 21.05%). All strains were resistant to almost all the antibiotics except polymyxin and tigacycline. Ten patients were treated with polymyxin or tigacycline based on their susceptibility results, and unfortunately 6 patients died. All strains exhibited a hyper-viscous phenotype, and the majority (17/19, 89.47%) of them contained rmpA and rmpA2. The serum killing test showed that KP9 was resistant to normal healthy serum, others were intermediately or highly sensitive. G. mellonella larvae infection assay suggested that the strains in this study were hypervirulent.

Conclusion

This study highlights the dominant strain and molecular epidemiology of hv-CRKP in a hospital in China. We should pay more attention to the effect of hv-CRKP on VAP, strengthen monitoring and control transmission.

Outer Membrane Vesicles Transmitting blaNDM-1 Mediate the Emergence of Carbapenem-Resistant Hypervirulent Klebsiella pneumoniae

Dissemination of hypervirulent and carbapenem-resistant Klebsiella pneumoniae (CRKP) has been reported worldwide, posing a serious threat to antimicrobial therapy and public health. Outer membrane vesicles (OMVs) act as vectors for the horizontal transfer of virulence and resistance genes. However, K. pneumoniae OMVs that transfer carbapenem resistance genes into hypervirulent K. pneumoniae (hvKP) have been insufficiently investigated. Therefore, this study investigates the transmission of the bla_NDM-1 gene encoding resistance via OMVs released from CRKP and the potential mechanism responsible for the carbapenem-resistant hypervirulent K. pneumoniae (CR-hvKP) emergence. OMVs were isolated via ultracentrifugation from CRKP with or without meropenem selective pressure. OMVs were then used to transform classical K. pneumoniae (ckp) ATCC 10031, extended-spectrum β-lactamase (ESBL)-producing K. pneumoniae ATCC 700603, and hvKP NTUH-K2044. Our results showed that meropenem treatment resulted in changes in the number and diameter of OMVs secreted by CRKP. OMVs derived from CRKP mediated the transfer of bla_NDM-1 to ckp and hvKP, thereby increasing the carbapenem MIC of transformants. Further experiments confirmed that NTUH-K2044 transformants exhibited hypervirulence. Our study demonstrates, for the first time, that OMVs derived from CRKP can carry bla_NDM-1 and deliver resistance genes to other K. pneumoniae strains, even hvKP. The transfer of carbapenem genes into hypervirulent strains may promote the emergence and dissemination of CR-hvKP. This study elucidates a new mechanism underlying the formation of CR-hvKP.

Epidemiological characteristics and molecular evolution mechanisms of carbapenem-resistant hypervirulent Klebsiella pneumoniae

Carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKP), a type of Klebsiella pneumoniae (KP) that exhibits hypervirulence and carbapenem resistance phenotypes, can cause severe infections, both hospital- and community-acquired infections. CR-hvKP has brought great challenges to global public health and is associated with significant morbidity and mortality. There are many mechanisms responsible for the evolution of the hypervirulence and carbapenem resistance phenotypes, such as the horizontal transfer of the plasmid carrying the carbapenem resistance gene to hypervirulent Klebsiella pneumoniae (hvKP) or carbapenemase-producing Klebsiella pneumoniae (CRKP) acquiring a hypervirulence plasmid carrying a virulence-encoding gene. Notably, KP can evolve into CR-hvKP by acquiring a hybrid plasmid carrying both the carbapenem resistance and hypervirulence genes. In this review, we summarize the evolutionary mechanisms of resistance and plasmid-borne virulence as well as the prevalence of CR-hvKP.

Emergence of a Hypervirulent Tigecycline-Resistant Klebsiella pneumoniae Strain Co-producing blaNDM–1 and blaKPC–2 With an Uncommon Sequence Type ST464 in Southwestern China

Emergence of bla_NDM–1 and bla_KPC–2 co-producing Klebsiella pneumoniae strains is currently attracting widespread attention, but little information is available about their tigecycline resistance, virulence, and prevalence in Southwest China. In July 2021, an extensively drug-resistant K. pneumoniae strain AHSWKP25 whose genome contained both bla_NDM–1 and bla_KPC–2 genes was isolated from the blood of a patient with the malignant hematological disease in Luzhou, China. We investigated the resistance profiles of AHSWKP25 using microbroth dilution, agar dilution, modified carbapenemase inactivation (mCIM), and EDTA-modified carbapenemase inactivation methods (eCIM). The virulence of AHSWKP25 was assessed through string tests, serum killing assays, and a Galleria mellonella larval infection model. Conjugation and plasmid stability experiments were conducted to determine the horizontal transfer capacity of plasmids. And efflux pump phenotype test and real-time quantitative reverse transcription-PCR (RT-PCR) were used to determine its efflux pump activity. Sequencing of AHSWKP25 determined that AHSWKP25 belonged to ST464, which is resistant to antibiotics such as carbapenems, tetracycline, fluoroquinolones, tigecycline, and fosfomycin. The efflux pump phenotype tests and RT-PCR results demonstrated that efflux pumps were overexpressed in the AHSWKP25, which promoted the tigecycline resistance of the bacteria. AHSWKP25 also showed hypervirulence and serum resistance in vitro model. AHSWKP25 carried several different plasmids that contained bla_NDM–1, bla_KPC–2, and mutated tet(A) genes. Sequence alignment revealed that the plasmids carrying bla_NDM–1 and bla_KPC–2 underwent recombination and insertion events, respectively. We demonstrated that an X3 plasmid carrying bla_NDM–1 was transferred from pSW25NDM1 to E. coli J53. We also identified missense mutations in the ramR, rcsA, lon, and csrD genes of AHSWKP25. Our results highlighted the potential of bla_NDM–1 and bla_KPC–2 co-producing K. pneumoniae strains to further develop antimicrobial resistance and hypervirulent phenotypes, but measures should be taken to closely monitor and control the spread of superbugs with multidrug-resistant phenotypes and hypervirulence.

Metagenomic Approaches Reveal Strain Profiling and Genotyping of Klebsiella pneumoniae from Hospitalized Patients in China

Klebsiella pneumoniae is a leading cause of highly drug-resistant infections in hospitals worldwide. Strain-level bacterial identification on the genetic determinants of multidrug resistance and high pathogenicity is critical for the surveillance and treatment of this clinically relevant pathogen. In this study, metagenomic next-generation sequencing was performed for specimens collected from August 2020 to May 2021 in Ruijin Hospital, Ningbo Women and Children’s Hospital, and the Second Affiliated Hospital of Harbin Medical University. Genome biology of K. pneumoniae prevalent in China was characterized based on metagenomic data. Thirty K. pneumoniae strains derived from 14 sequence types were identified by multilocus sequence typing. The hypervirulent ST11 K. pneumoniae strains carrying the KL64 capsular locus were the most prevalent in the hospital population. The phylogenomic analyses revealed that the metagenome-reconstructed strains and public isolate genomes belonging to the same STs were closely related in the phylogenetic tree. Furthermore, the pangenome structure of the detected K. pneumoniae strains was analyzed, particularly focusing on the distribution of antimicrobial resistance genes and virulence genes across the strains. The genes encoding carbapenemases and extended-spectrum beta-lactamases were frequently detected in the strains of ST11 and ST15. The highest numbers of virulence genes were identified in the well-known hypervirulent strains affiliated to ST23 bearing the K1 capsule. In comparison to traditional cultivation and identification, strain-level metagenomics is advantageous to understand the mechanisms underlying resistance and virulence of K. pneumoniae directly from clinical specimens. Our findings should provide novel clues for future research into culture-independent metagenomic surveillance for bacterial pathogens.

IMPORTANCE Routine culture and PCR-based molecular testing in the clinical microbiology laboratory are unable to recognize pathogens at the strain level and to detect strain-specific genetic determinants involved in virulence and resistance. To address this issue, we explored the strain-level profiling of K. pneumoniae prevalent in China based on metagenome-sequenced patient materials. Genome biology of the targeted bacterium can be well characterized through decoding sequence signatures and functional gene profiles at the single-strain resolution. The in-depth metagenomic analysis on strain profiling presented here shall provide a promising perspective for culture-free pathogen surveillance and molecular epidemiology of nosocomial infections.

Emergence of Tigecycline Nonsusceptible and IMP-4 Carbapenemase-Producing K2-ST65 Hypervirulent Klebsiella pneumoniae in China

Carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKP) poses a significant public health challenge worldwide, but research on IMP-producing CR-hvKP and its tigecycline resistance is extremely scarce. We report herein the recovery of two IMP-4–producing, capsular serotype K2, sequence type 65 (K2-ST65), hypervirulent K. pneumoniae isolates (C1672 and C2051), which caused severe and fatal infections in ICU patients, after retrospectively screening 3,285 carbapenem-resistant K. pneumoniae isolates from 26 provinces in China. Notably, C2051 also demonstrated tigecycline nonsusceptibility, mediated by a frameshift mutation in the TetR/AcrR family transcriptional regulator. Both strains harbored bla_IMP-4 and critical plasmid-borne virulence genes (rmpA/rmpA2, iucA, and iroN) and demonstrated high virulence in Galleria mellonella, indicating CR-hvKP. The bla_IMP-4 gene was located on the IncU- and IncN-type plasmids, which showed high stability in C1672 and C2051 after serial passage for 5 days, with retention rates of 87% and 93.7%, respectively. No significant differences in growth rates were observed among the parental strains and the corresponding resistance plasmid-cured mutants (P = 0.5273), suggesting that strains carrying the bla_IMP and virulence plasmids have the potential to exist for a long time without compromising fitness. The genetic environments of the bla_IMP-4 gene in both strains were similar, and it has been inferred that the genetic regions of bla_IMP-4 were inserted into different backbones. Several conjugal transfer genes, such as traO, traE, traN, and traBCD, were identified in the bla_IMP-4-bearing plasmid of C2051, suggesting a higher ability for plasmid transmission. The convergence of IMP carbapenemase and tigecycline nonsusceptibility in a classic hypervirulent K. pneumoniae lineage highlights the need to enhance clinical awareness and epidemiologic surveillance.

IMPORTANCE To date, research on IMP-producing CR-hvKP is extremely scarce. Only one case of urinary tract infection caused by an IMP-6–producing K1-ST23 hypervirulent K. pneumoniae isolate in Japan was recorded, with a limited description of clinical information and genomic features. None of the published studies examined the virulence of the reported strains or the stability and fitness of resistance plasmids or presented a phylogenetic analysis. This dearth of data is notable because CR-hvKP infections are increasingly identified, but critical characteristics of the emerging resistance mediated by IMP carbapenemases in CR-hvKP remain unknown. Here, we report the emergence of two IMP-4 carbapenemase-producing K2-ST65 hypervirulent K. pneumoniae isolates that caused severe and fatal infections in clinical settings in China. Notably, one of them also demonstrated tigecycline nonsusceptibility. These strains carrying bla_IMP and virulence plasmids had the potential to exist for a long time without compromising their fitness, highlighting the urgent need to enhance clinical awareness and epidemiologic surveillance to prevent their dissemination.