Pathogenic bacteria continually evolve under antimicrobial pressure through acquired resistance genes, making it crucial to understand their evolutionary strategies. We identify a clinical Klebsiella pneumoniae isolate resistant to ceftazidime/avibactam (CZA), harboring heterogeneous multicopy bla CTX-M , among which a bla CTX-M-249 variant mediates CZA resistance. Both bla CTX-M-249 and its closely related allele bla CTX-M-65 are dominant within the clonal population and are located at two loci on the same plasmid, with their proportions shifting under antibiotic pressure. Using experimental and mathematical models, we demonstrate that the heterogeneous arrangement of bla CTX-M variants on the same plasmid confers greater stability and competitive advantage than that across separate plasmids, particularly during drug switching. Re-analysis of large genomic datasets supports the universality of this phenomenon. Our findings reveal an evolutionary strategy in which β-lactamase genes, through multicopy heterogeneity on a single plasmid, ensure stable inheritance of resistance and enhance bacterial adaptability under fluctuating clinical antibiotic pressures.

OBJECTIVES:Carbapenem-resistant Acinetobacter baumannii (CRAB) is a major cause of hospital- and ventilator-associated pneumonia (HAP/VAP) with limited treatment options. Eravacycline (ERA) shows potent in vitro activity and favorable pulmonary pharmacokinetics, but clinical evidence for CRAB HAP/VAP remains scarce. We evaluated the real-world effectiveness and safety of ERA. METHODS:We conducted a retrospective multicenter cohort study at 12 hospitals in China (April 2022-March 2024). Adults with microbiologically confirmed CRAB HAP/VAP treated with ERA or best available therapy (BAT) for ≥ 4 days were propensity scores matched. Primary outcomes were clinical success at end of treatment (EOT) and 28-day mortality. RESULTS:After 3349 patients screened, 382 were included (ERA 204; BAT 178). Baseline characteristics were balanced. Clinical success at EOT was higher with ERA than BAT (63.2% vs 55.1%), while 28-day mortality was similar (40.1% vs 42.0%). ERA achieved higher microbiological eradication at EOT (45.1% vs 32.0%) and day 14 (36.8% vs 22.5%). Adverse events occurred less frequently with ERA. In targeted first-line treatment, ERA showed higher clinical success, greater microbiological eradication and faster clinical response without increased mortality. CONCLUSION:Eravacycline improved microbiological clearance, clinical response, and safety compared with BAT for CRAB HAP/VAP, particularly when used as targeted first-line therapy.

BACKGROUND:This study investigate the molecular epidemiology and population characteristics of 184 Acinetobacter baumannii clinical isolates collected in Zhejiang (2015-2020), shedding light on the persistence and success of ST208-KL2 lineage. METHODS:Whole-genome sequencing and bioinformatic analysis characterized the population structure and transmission dynamics of 184 A. baumannii. Plasmid analysis identified the surrounding structures of blaOXA-58 and blaNDM-1 genes. Serum inhibition assays and Galleria mellonella virulence experiments, combined with global epidemiological analysis, explored the persistence and dominance of ST208-KL2. RESULTS:Of the isolates, approximately 78.8% (145/184) exhibited carbapenem resistance, primarily driven by blaOXA-23, blaOXA-72, blaOXA-58, and blaNDM-1. The A. baumannii population was divided into 2 clusters, distinguished by differences in ST types and resistance islands profiles. Cluster2 accounted for 71 department-time transmission events, mainly involving long-term interdepartmental spread, particularly in the rehabilitation medicine department and intensive care unit. Recombination analysis revealed that recombination occurred mainly in capsular locus (KL) regions, prophage regions, and predicted protein regions. Phenotypic experiments found that ST208-KL2 isolates displayed increased virulence and greater resistance to serum inhibition compared to ST208-KL7 isolates. This finding likely explains its persistently higher prevalence throughout the study period, except in 2019. CONCLUSIONS:Cluster2 isolates demonstrated significant advantages in ARG prevalence, resistance rates, and transmission capacity. ST208-KL2, with its superior serum resistance and virulence compared to ST208-KL7, has emerged as a dominant lineage with global implications for infection control and public health.

Background: The transmission of carbapenem-resistant Pseudomonas aeruginosa (CRPA) between hospital environment and patients poses significant challenges for clinical management. The COVID-19 pandemic may have influenced bacterial transmission dynamics in intensive care units (ICU). This study aimed to prospectively investigate the temporal and spatial spread of P. aeruginosa after a COVID-19 upsurge period in China. Methods: We routinely screened for P. aeruginosa in both the environment and patients in a newly-opened 21-bed tertiary teaching hospital ICU in eastern China from October 2022 to April 2023, during which a COVID-19 upsurge occurred from December 2022 to January 2023. Whole-genome sequencing and antibiotic susceptibility testing were performed on all non-repetitive P. aeruginosa isolates. Results: Among 1694 environmental samples, 40 (2.36%) samples were CRPA. In 1576 nasopharyngeal and rectal samples (from 353 patients), 108 samples (6.86%) were CRPA. Sequence type (ST) 463 was the most prevalent clone in both patient and environmental samples. Spatiotemporal distribution and genomic data revealed sporadic patients-related transmission before COVID-19 upsurge period, while high-risk ST463 clone transmission was detected during COVID-19 upsurge period. However, there was no strong evidence to show that antibiotic consumption significantly influenced CRPA transmission in this study. Additionally, the evolution events of blaKPC (from blaKPC-2 to blaKPC-71) were observed, resulting in multi-sites CRPA colonization in one patient. Conclusion: Our prospective study demonstrates that COVID-19 upsurge is associated with increased P. aeruginosa transmission. These findings provide valuable insights into nosocomial infection management during future public health crisis. We also reported carbapenemase mutation from blaKPC-2 to blaKPC-71 in P. aeruginosa, which provides reference for further antibiotic usage.

OBJECTIVES:Hypervirulent Klebsiella pneumoniae (hvKp) ST23-K1 poses a global health threat due to its high virulence and increasing antimicrobial resistance. This study aimed to characterise the genomic feature and phylogenetic evolution of ST23-K1 in China. METHODS:K1 isolates from a nationwide epidemiological surveillance project underwent whole-genome sequencing. Virulence was assessed using hypermucoviscosity phenotyping and a murine infection model. For ST23-K1 carrying acquired antimicrobial resistance genes (ARGs), the CRISPR/Cas system, protospacers, anti-CRISPR (Acr) genes, and plasmidome were characterised. Time-resolved phylogenetic analysis was performed using integrated locally generated and publicly available data. RESULTS:Among 400 K1 isolates, ST23 was the most prevalent sequence type, and its effective population size increased following CG23-I divergence. The CG23-I sub-lineage was widely distributed nationwide with limited evidence of clonal transmission. Isolates with an incomplete cps locus exhibited significantly reduced virulence compared with those carrying an intact locus. The prevalence of extended-spectrum β-lactamase-positive ST23-K1 isolates increased over time, whereas carbapenemase-producing isolates remained stable. Among acquired ARGs-positive ST23-K1 isolates, a conserved protospacer corresponding to a prevalent spacer was identified. This protospacer, together with AcrIE genes, was frequently co-located on IncFII-type plasmids. CONCLUSION:ST23-K1 remains a hypervirulent lineage undergoing ongoing evolutionary expansion. The presence of acquired ARGs in ST23-K1 may be associated with AcrIE-harbouring IncFII plasmids, and functional validation is required to clarify the underlying mechanisms. Continuous genomic surveillance is essential to monitor the evolution and antimicrobial resistance trends of ST23-K1.

BACKGROUND:KPC and NDM co-producing carbapenem-resistant Klebsiella pneumoniae (KN-CRKP) is an escalating global health threat with limited treatment options. METHODS:Here, we conducted a multicentre retrospective case-control study on KN-CRKP in China (2020-2025), collecting 3012 non-duplicated CRKP isolates, of which 71 (2.4%) were KN-CRKP. For clinical analysis, 39 patients with KN-CRKP infections were identified from 71 isolates and matched in a 1:2 ratio with 78 patients infected by KPC-2-producing CRKP. For global analysis, we retrieved 100,141 genomes from GenBank, of which 662 non-redundant KN-CRKP sequences were combined with our 71 KN-CRKP isolates. Antimicrobial susceptibility testing, whole-genome sequencing (WGS), plasmid transfer and stability, fitness cost, transcriptomics and Bayesian phylogeography were used to investigate evolution mechanisms and molecular epidemiology of KN-CRKP strains. FINDINGS:Among the infected patients, hospital-acquired or ventilator-associated pneumonia was the most common (41.0%, 16/39). Patients with KN-CRKP infections had a non-significantly higher 28-day mortality (38.5%, 15/39) than the KPC-CRKP control group (24.4%, 19/78; p = 0.133), but a significantly higher in-hospital mortality (46.2%, 18/39 vs. 25.6%, 20/78; p = 0.036). Independent risk factors included diabetes, a history of CRO (carbapenem-resistant gram-negative organism) infection treated with ceftazidime-avibactam (CZA) treatment, and recent use of β-lactam/β-lactamase inhibitor combinations. All KN-CRKP isolates were resistant to carbapenems and CZA, but exhibited highly susceptible to colistin (98.6%), cefiderocol (94.4%), and aztreonam-avibactam (100%). The predominant KN-CRKP clones were ST11 (73.2%) and ST307 (15.5%). Global surveillance of 733 global KN-CRKP identified ST11 as a pandemic lineage diverging into China/Brazil subclusters, with emerging clones ST147/ST307 showing post-pandemic increases. Plasmid profiling revealed blaNDM mainly on IncX3/IncN plasmids and blaKPC on IncR/IncFII plasmids, with novel hybrid plasmids carrying both carbapenemases identified. blaNDM-carrying plasmids had higher transferability/stability than blaKPC-carrying ones. In vitro experiments confirmed blaNDM transfer from Citrobacter freundii to blaKPC-carrying K. pneumoniae, forming KN-CRKP. INTERPRETATION:The high mortality and global prevalence of KN-CRKP emphasise the need for enhanced surveillance and infection control globally. FUNDING:National Natural Science Foundation of China (82472323 and 82172306), Zhejiang Province Natural Science Foundation of China (LQN26H200003, LR25H200001, LQN25H200002, MS25H190009), the "Pioneer" and "Leading Goose" R&D Program of Zhejiang Province (2025C02187), the Zhejiang Provincial Medical and Health Technology Project (2025HY0224) and Zhejiang Provincial Disease Prevention and Control Science and Technology Program (2025JK063). We appreciate the statistical support provided by Hui Liu (Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang, China).

OBJECTIVES:This study aimed to investigate the "seesaw effect" of daptomycin (DAP) and ceftobiprole (BPR) on DAP-resistant (DAP-R) methicillin-resistant Staphylococcus aureus (MRSA) isolates. METHODS:Broth microdilution minimum inhibitory concentrations (MICs) of DAP and BPR were tested for laboratory-derived and clinical DAP-R MRSA isolates to estimate the "seesaw effect." Time-kill curves for seven representative DAP-R isolates were obtained using DAP and BPR to validate their synergistic activity in vitro. Whole genome sequencing as well as deletion and complementation of the mprF gene were performed to investigate the mechanisms of the "seesaw effect." RESULTS:The BPR MICs decreased by half-fold in DAP-R MRSA isolates. The synergistic effect of DAP and BPR against representative clinical and community-associated MRSA (CA-MRSA) isolates was demonstrated in time-kill analyses, showing that synergistic activity was preferred in CA-MRSA compared with hospital-associated MRSA. The mprF mutations were identified in isolates exhibiting the "seesaw effect." These mutations increased the DAP MIC while decreasing the BPR MIC. CONCLUSIONS:The "seesaw effect" between DAP and BPR was prevalent among DAP-R MRSA isolates. This phenomenon was associated with the mprF mutations of MRSA.

Polymyxin B, a last resort for carbapenem-resistant gram-negative bacteria (CRGNB) infections, has infection site-specific pharmacokinetic/pharmacodynamic (PK/PD) properties. However, there is little clinical evidence to support optimal exposures of polymyxin B for different site infections. We performed a prospective, observational, multicenter study to evaluate the clinical outcomes and PK/PD of intravenous polymyxin B treatment for various site CRGNB infections. The main clinical outcomes were 14-day all-cause mortality and nephrotoxicity, and the secondary outcomes were 28-day mortality and clinical response. The area under curves (AUCs) of polymyxin B were determined, and their associations with clinical outcomes were analyzed by stratification based on the infection site. A total of 312 patients were ultimately enrolled from 10 research centers. The overall 14-day mortality was 29.5%, and those of patients with lower respiratory tract infection (LRTI), intra-abdominal infection (IAI), and bloodstream infection (BSI) were 32.3%, 19.7%, and 30.3%, respectively. The 28-day mortality rate was 38.1%, while LRTI patients had the highest mortality (41.4%) and IAI patients lowest (34.8%). The clinical response rate was 46.2%, which was similar among the subgroups. The overall AKI rate was 60.9%. An AUC greater than 50 mg∙h/L was related to lower mortality in IAI patients but not in LRTI patients, which led to a lower but not significant difference in the overall analysis. The AUC of polymyxin B was an independent risk factor for 14-day mortality in IAI patients, and the cutoff value was 76 mg∙h/L. The results would be helpful for personalized dosing and monitoring of polymyxin B.CLINICAL TRIALSThis study is registered with the Chinese Clinical Trial Registry as ChiCTR2200056667.

CRKP infections are a significant public health threat due to their high mortality and limited treatment options. This study aimed to investigate CRKP colonization and clonal dissemination mechanism in an ICU. From August 2019 to December 2019, 8668 samples were collected from patients and the ICU environment for CRKP screening. Positive samples underwent antimicrobial susceptibility testing, whole-genome sequencing, and molecular epidemiological analysis. Disinfectant sensitivity and ultraviolet (UV) resistance experiments were conducted to evaluate clonal persistence. The overall CRKP positive rate was 4.85% (420/8668), with higher rates in patients (14.77%, 247/1672) compared to environmental surfaces (2.47%, 173/6996). Intestinal and ventilator-related surfaces were identified as high-risk colonization sites. Molecular analysis revealed six sequence types, with ST11-KL64 (44.05%, 185/420) and ST15-KL112 (24.05%, 101/420) as dominant clones, both exhibiting elevated virulence. Notably, the emerging ST15-KL112 clone demonstrated enhanced resistance to disinfectants including chlorhexidine (MIC 8 mg/L) and benzalkonium chloride (32 mg/L). While most isolates produced KPC-2 (72.86%), OXA-232 prevalence (25.23%) exceeded prior reports. Crucially, ST11 strains survived standard UV disinfection (60-second exposure) at rates 1.3- to 5-fold higher than other clones (p < 0.01). Our findings highlight the critical role of disinfectant resistance in sustaining CRKP transmission. To mitigate outbreaks, we advocate for disinfectant rotation protocols targeting disinfectant-resistant clones and prolonged UV exposure times in ICUs. The persistence of resistant CRKP clones in the ICU environment, particularly their high tolerance to disinfectants, highlights the urgent need for enhanced infection control strategies, including tailored disinfection protocols and surveillance programs.

Pseudomonas aeruginosa is a major multidrug-resistant pathogen whose biofilm formation complicates treatment. P. aeruginosa r ugose s mall c olony v ariants (RSCVs), characterized by enhanced biofilm production and resistance, pose significant clinical challenges. However, the formation mechanisms remain unclear in clinical strains. Paired clinical P. aeruginosa isolates AR8023-1 (wild-type) and AR8023-2 (RSCV) were collected from urine samples of a neurosurgery inpatient chronologically. The genome comparison was performed using Breseq, and plasmid complementation was performed to construct complemented strain (AR8023-2 RifR :: wspA AR8023-1 ). Then, all the aforementioned strains were examined RSCV phenotype, biofilm formation, and motility, and gene expression differences induced by the wspA mutation were analyzed via transcriptome sequencing, followed by quantification of c-di-GMP. In addition, we assessed antimicrobial susceptibility of the strains under both planktonic and biofilm conditions. The results showed that both AR8023-1 and AR8023-2 were identified as ST3420. AR8023-1 exhibited typical smooth morphology, while AR8023-2 displayed a RSCV phenotype. A single SNP difference was identified between the two strains, characterized by a deletion of glutamine at position 289 (CAG triplet deletion) in the wspA gene of strain AR8023-2. The complement isolates restored wild-type morphology, motility, and biofilm formation. Transcriptomics revealed a significant upregulation of c-di-GMP metabolic genes in RSCVs ( P < 0.001), indicating that the WspAΔ289Q mutation activates diguanylate cyclase (DGC) activity, thereby elevating c-di-GMP synthesis. Intracellular c-di-GMP levels were significantly higher in RSCVs than those in WT and complement isolates, respectively ( P < 0.001). Consequently, biofilm susceptibility testing demonstrated the β-lactams MBIC of RSCVs was ≥8–512-fold higher than those of WT and complement isolates. This study identifies a clinical WspAΔ289Q mutation that elevates c-di-GMP, driving RSCV formation and biofilm-mediated resistance. P. aeruginosa is a leading multidrug-resistant pathogen whose biofilm formation capability greatly complicates treatment outcomes. This study identifies a novel clinical mutation in the wspA gene (WspAΔ289Q) that drives the emergence of rugose small colony variants (RSCVs), a phenotype linked to heightened biofilm production and antimicrobial resistance. We demonstrate that this mutation upregulates cyclic di-GMP synthesis, leading to increased biofilm formation and markedly reduced susceptibility to β-lactam antibiotics under biofilm conditions. These results provide important insights into the genetic basis of RSCV development in clinical settings and highlight the role of c-di-GMP signaling in biofilm-associated resistance. Our findings underscore the need to target c-di-GMP pathways as a potential strategy for combating persistent P. aeruginosa infections.

BACKGROUND:Intensive care units (ICUs) face high risks of methicillin-resistant Staphylococcus aureus (MRSA) transmission, yet how accessory gene regulator (agr) dysfunction drives strain adaptation remains unclear. This study investigated MRSA epidemiology in a new ICU, focusing on post-COVID-19 clonal dynamics. METHODS:We conducted 6-month prospective surveillance (Oct 2022-Apr 2023) in a Chinese tertiary ICU. Biweekly environmental/patient sampling and admission/discharge screenings were performed. Isolates underwent whole-genome sequencing (WGS), core-genome multilocus sequence typing (cgMLST), antimicrobial susceptibility testing, and functional assays (CAMP/biofilm). RESULTS:MRSA colonization rates were 5.98% (environment) and 3.86% (patients), with 6.8% present on admission (POA) and 7.6% ICU-associated colonization. Dominant clonal complex (CC) 5 (65.33%) comprised sequence type (ST) 764 (pre-COVID-19) and ST5 (post-COVID-19). cgMLST identified 18 transmission clusters (cgSNP <15), revealing that CC5 isolates mainly originated from environmental reservoirs (beds, medical instruments). ST5 displaced ST764 post-COVID-19, mediated by an agrC mutation (agrC-T43I) that enhanced environmental fitness via increased biofilm formation and reduced antimicrobial susceptibility. ICU-associated colonization shifted toward CC5 (64% vs 30% POA), confirming nosocomial adaptation. CONCLUSIONS:Environmental contamination is the primary source of MRSA transmission in ICUs. The agrC-T43I mutation drives ST5 dominance post-pandemic by enhancing biofilm-dependent persistence, underscoring the need for genomic surveillance to guide infection control.

To investigate the mechanisms of ceftazidime/avibactam (CZA) resistance and the nosocomial dissemination of carbapenem-resistant Pseudomonas aeruginosa (CRPA) and carbapenem-resistant Klebsiella pneumoniae (CRKP) in an intensive care unit (ICU) in China. Clinical CRPA and CRKP isolates were obtained from an ICU of a tertiary hospital in China from August 2020 to February 2021. Antimicrobial susceptibility was determined according to CLSI. WGS, cloning experiments and kinetic parameters were conducted to reveal resistance mechanisms, molecular characteristics and dissemination of CRPA and CRKP. We isolated 32 CZA-resistant strains, including 12 CRPA and 20 CRKP strains from an ICU between August 2020 and February 2021. CZA resistance was associated with the presence of NDM and efflux pumps in CRKP strains, whereas blaAFM-2, blaKPC-87, and blaPER-1 contributed to CZA resistance in CRPA strains. Compared to KPC-2, KPC-87 exhibited a 1.5-fold elevation in kcat/Km for ceftazidime, a 7.5-fold increase in Ki for avibactam, and a loss of carbapenem hydrolysis. blaKPC-87 was located in the NTEKPC-IIa like element based on the Tn3. Insertion of 656 bp ΔblaTEM-1 upstream of blaKPC-87 introduced an additional promoter that increased KPC-87 expression. Cluster 2 and 3 of CRKP represented two different clones of ST11 transmitted between patients. KPC-87-producing ST270 CRPA strains exhibited a small-scale dissemination and cross-regional transfer with the referral of a patient. The evolutionary pathways of AFM-2-producing ST275 CRPA strains were more complex to elucidate the transmission events. In CRKP and CRPA, diverse resistance mechanisms contributed to CZA resistance. These CZA-resistant strains were transmitted among patients in the ICU and even across regions to the other healthcare unit when the patient was transferred.

As a widely spread Gram-negative bacteria, Klebsiella pneumoniae (KP) mainly causes acquired infections in hospitals, such as lung infections, urinary tract infections, and bloodstream infections. In recent years, the number of multidrug-resistant KP strains has increased dramatically, posing a great threat to human health. Carbapenem-resistant KP (CRKP) can be colonized in human body, especially in gastrointestinal tract, and some colonized patients can be infected during hospitalization, among which invasive operation, underlying disease, admission to intensive care unit, antibiotic use, severity of the primary disease, advanced age, operation, coma, and renal failure are common risk factors for secondary infection. Active screening and preventive measures can effectively prevent the occurrence of CRKP infection. Based on the epidemiological status, this study aims to discuss the correlation between colonization and secondary infection induced by CRKP and risk factors for their happening and provide some reference for nosocomial infection prevention and control.

OBJECTIVE:To investigate clinical characteristics of hematological malignancy (HM) patients with carbapenem-resistant gram-negative organism (CRO) bloodstream infections (BSI) in China, and to elucidate the prognostic risk factors of CRO BSI. METHODS:We conducted a multicenter case-control study of 201 HM patients with CRO BSI between 2018-2020. Antimicrobial susceptibility testing and whole genome sequencing were performed for CRO isolates. Independent risk factors for 28-day crude mortality were analyzed using Cox proportional hazards regression models. The subgroups of major species were also evaluated. RESULTS:The pathogens responsible for CRO BSI in HM patients dominated by ST11 CRKP, ST167 CREC and ST463 CRPA. Most isolates produced carbapenemases with KPC and NDM being the main. CRO isolates had resistance rates to conventional antimicrobials ranging from 55%-100% and poor susceptibility to novel antimicrobials related to carbapenemases and species. The 28-day crude mortality was 24.2%. Non-Hodgkin lymphoma, heart disease, blaKPC-2 positive, empirical antibiotic therapy with linezolid, Pitt bacteremia score >3.5 were risk factors for 28-day mortality and appropriate definitive antibiotic therapy, tigecycline-containing therapy and aminoglycoside-containing therapy were protective factors. blaKPC-2 positive in CRKP and ST463 in CRPA were associated with Pitt bacteremia score >3.5. Solid tumor and other site infections before BSI were risk factors for ST463 CRPA BSI and pulmonary infection before BSI was risk factor for KPC-KP BSI. CONCLUSIONS:The antimicrobial resistance of CRO isolates for BSI in HM patients is critical. HM patients with CRO BSI should be treated with appropriate definitive antibiotic therapy based on early clarification of pathology and their antimicrobial susceptibility.

To investigate the epidemiology of ST20 carbapenem-resistant Klebsiella pneumoniae (CRKP) in China, and further explore the genomic characteristics of bla(IMP-4) and bla(NDM-1) coharboring isolates and plasmid contributions to resistance and fitness. Seven ST20 CRKP isolates were collected nationwide, and antimicrobial susceptibility testing was performed. Antimicrobial resistance genes, virulence genes, and plasmid replicons were identified via whole-genome sequencing, and clonality assessed via core-genome multilocus sequence typing. Furthermore, we found four dual-metallo-beta-lactamases (MBL)-harbouring isolates, the gene location was detected by Southern blotting, and plasmid location analysis showed that bla(IMP-4) was located on a separate plasmid, a self-conjugative fusion plasmid, or the bacterial chromosome. These isolates were subjected to long-read sequencing, the presence of bla(IMP-4) in different locations was identified by genomic comparison, and transposon units were detected via inverse PCR. We subsequently found that bla(IMP-4) on the fusion plasmid and bacterial chromosome was formed via intact plasmid recombination by the IS26 and ltrA, respectively, and the circular transposon unit was related to cointegration, however, bla(IMP-4) in different locations did not affect the gene stability. The bla(NDM-1)-harbouring plasmid contributed to the increased resistance to beta-lactams and shortened survival lag time which was revealed in plasmid cured isolates. In summary, the K. pneumoniae ST20 clone is a high-risk resistant clone. With the use of ceftazidime/avibactam, MBL-positive isolates, especially dual-MBL-harbouring isolates, should be given additional attention.

Objectives Carbapenem-resistant Klebsiella pneumoniae (CRKP) is a major nosocomial infectious pathogen with rapidly increasing prevalence. The genomic epidemiological characteristics of CRKP nationwide, especially the evolving trends within the predominant clones, should be evaluated clearly.Methods We collected 3415 K. pneumoniae strains from 28 hospitals across China. Antimicrobial susceptibility testing and WGS were performed. Subsequent genomic analyses, including sequence typing, K-locus (KL) identification, antimicrobial resistance gene screening, and virulence score assessment were performed. The phylogenetic relationship of clonal group 11 was determined based on core-genome analysis, and the presence of the pLVPK-like virulence plasmid in ST11 isolates was confirmed using plasmid core-gene analysis. Additionally, the trends of the ST11 lineage with different KL types on a global scale were investigated using Beast2.Results Of the K. pneumoniae strains, 708 were identified as CRKP isolates (20.7%), of which 97.7% were MDR. ST11 was the predominant clone, and KPC-2 was the prevalent carbapenemase in China, although the prevalence of specific clones and carbapenemases varied by geographic region. Among ST11 isolates, KL47 and KL64 were the predominant KL types, and KL64 gradually replaced KL47, with a higher percentage of KL64 isolates harbouring the pLVPK-like plasmid. Global genome data showed a significant increase in the effective population size of KL64 over the last 5 years.Conclusions The prevalence of CRKP was very high in certain regions in China. The increasing convergence of virulence and resistance, particularly in ST11-KL64 isolates, should be given more attention and further investigation.

Siderophore is a group of low molecular weight compounds with high affinity for ferric iron, which could facilitate bacterial iron consumption. Similarly, hemin/heme scavenged by the hemin uptake system HmuRSTUV usually act as another critical iron source for K. pneumoniae .

Ceftazidime-avibactam is a novel β-lactam–β-lactamase inhibitor (BLBLI) combination with powerful activity against Enterobacterales isolates producing AmpC, such as CMY-like cephalosporinase. However, in recent years, CMY variants have been reported to confer ceftazidime-avibactam resistance.

In this study, we aimed to clarify the evolutionary trajectory of a Klebsiella pneumoniae carbapenemase (KPC)-producing Klebsiella pneumoniae (KPC-Kp) population during β-lactam antibiotic therapy. Five KPC-Kp isolates were collected from a single patient.