Global phylogeography and genomic characterization of blaKPC and blaNDM-positive clinical Klebsiella aerogenes isolates from China, 2016-2022.

Carbapenem-resistant Klebsiella aerogenes (CRKA), being one of the members of carbapenem-resistant Enterobacteriaceae (CRE), has caused great public health concern, but with fewer studies compared to other CRE members. Furthermore, studies on phylogenetic analysis based on whole genome Single-Nucleotide Polymorphism (SNP) of CRKA were limited. Here, 20 CRKA isolates (11 blaKPC-2-bearing and 9 blaNDM-1/5-harboring) were characterized by antimicrobial susceptibility testing, conjugation assay, whole genome sequencing (WGS) and bioinformatics analysis. Additionally, the phylogeographic relationships of K. aerogenes were further investigated from public databases. All isolates were multidrug-resistant (MDR) bacteria, and they demonstrated susceptibility to colistin. Most blaKPC-2 or blaNDM-1/5-carrying plasmids were found to be conjugative. Phylogenetic analysis revealed the clonal dissemination of K. aerogenes primarily occurred within clinical settings. Notably, some strains in this study showed the potential for clonal transmission, sharing few SNPs between K. aerogenes and KPC- and/or NDM-positive K. aerogenes isolated from various countries. The STs of K. aerogenes strains had significant diversity. WGS analysis showed that the IncFIIK plasmid was the most prevalent carrier of blaKPC-2, and, blaNDM-1/5 were detected on the IncX3 plasmids. The Tn6296 and Tn3000 transposons were most common vehicles for facilitating the transmission of blaKPC-2 and blaNDM-1/5, respectively. This study highlights the importance of continuous screening and surveillance by WGS for analysis of drug-resistant strains in hospital settings, and provide clinical information that supports epidemiological and public health research on human pathogens.

Genomic epidemiology and ceftazidime-avibactam high-level resistance mechanisms of Pseudomonas aeruginosa in China from 2010 to 2022.

Ceftazidime-avibactam (CZA) resistance is a huge threat in the clinic; however, the underlying mechanism responsible for high-level CZA resistance in Pseudomonas aeruginosa (PA) isolates remains unknown. In this study, a total of 5,763 P. aeruginosa isolates were collected from 2010 to 2022 to investigate the ceftazidime-avibactam (CZA) high-level resistance mechanisms of Pseudomonas aeruginosa (PA) isolates in China. Fifty-six PER-producing isolates were identified, including 50 isolates carrying blaPER-1 in PA, and 6 isolates carrying blaPER-4. Of these, 82.1% (46/56) were classified as DTR-PA isolates, and 76.79% (43/56) were resistant to CZA. Importantly, blaPER-1 and blaPER-4 overexpression led to 16-fold and >1024-fold increases in the MICs of CZA, respectively. WGS revealed that the blaPER-1 gene was located in two different transferable IncP-2-type plasmids and chromosomes, whereas blaPER-4 was found only on chromosomes and was carried by a class 1 integron embedded in a Tn6485-like transposon. Overexpression of efflux pumps may be associated with high-level CZA resistance in blaPER-1-positive strains. Kinetic parameter analysis revealed that PER-4 exhibited a similar kcat/Km with ceftazidime and a high (∼3359-fold) IC50 value with avibactam compared to PER-1. Our study found that overexpression of PER-1 combined with enhanced efflux pump expression and the low affinity of PER-4 for avibactam contributes to high-level resistance to CZA. Additionally, the Tn6485-like transposon plays a significant role in disseminating blaPER. Urgent active surveillance is required to prevent the further spread of high-level CZA resistance in DTR-PA isolates.

Characterization of a novel Tn6485h transposon carrying both blaIMP-45 and blaAFM-1 integrated into the IncP-2 plasmid in a carbapenem-resistant Pseudomonas aeruginosa.

OBJECTIVES: To characterize a carbapenem-resistant Pseudomonas aeruginosa (CRPA) with an IncP-2 plasmid containing a novel transposon, Tn6485h, which carries both blaIMP-45 and blaAFM-1. METHODS: Antimicrobial susceptibility testing and filter mating experiment were performed on PA942. The stability of the plasmid carrying both blaIMP-45 and blaAFM-1 was carried out. We determined the growth rate of the transconjugant to investigate fitness cost. Additionally, whole-genome sequencing and genomic analysis were performed on PA942. RESULTS: PA942 strain was resistant to most antibiotics except for ciprofloxacin and colistin. Bioinformatics analysis confirmed that PA942 contains an IncP-2 plasmid with a novel transposon Tn6485h carrying both blaIMP-45 and blaAFM-1. The plasmid pPA942-IMP45 can be transferred into recipient bacteria PAO1Rif with an efficiency of 2.2 × 10-7 and the transconjugant PAO1Rif/ pPA942-IMP45 can be stably inherited for 10 generations in the absence of antibiotics. CONCLUSION: We report a carbapenem-resistant P. aeruginosa strain with an IncP-2 plasmid containing a novel transposon, Tn6485h, which carries both blaIMP-45 and blaAFM-1. The IncP-2 plasmid and transposon Tn6485h may contribute to the spread of MBL genes. Therefore, effective measures to prevent the spread of these plasmids should be taken.

Molecular characterization and comparison of bla NDM-1-carrying and bla NDM-5-harboring IncX3-type plasmids in carbapenem-resistant Klebsiella pneumoniae.

Carbapenem-resistant Klebsiella pneumoniae (CRKP), which harbors the bla NDM plasmid, has been reported extensively and is considered a global threat clinically. However, characterization and comparisons of bla NDM-1-carrying and bla NDM-5-harboring IncX3-type plasmids in CRKP are lacking. Here, we systematically compared the differences in the characteristics, genetic backgrounds, transferability, and fitness costs between bla NDM-1-carrying and bla NDM-5-carrying plasmids in K. pneumoniae isolates. Fifteen NDM-producing CRKP isolates were recovered from 1376 CRKP isolates between 2019 and 2021, of which 4 were positive for bla NDM-1 and 11 were positive for bla NDM-5. All strains were highly resistant to carbapenem but remained susceptible to tigecycline and colistin. Core-genome-based phylogenetic analyses revealed that these strains were not clonally related. Whole-genome sequencing showed that bla NDM-1 and bla NDM-5 were located on ~54 kb and ~46 kb IncX3-type plasmids, respectively. The backbone, genetic context, and fitness cost of the bla NDM-1-bearing plasmid were highly similar to those of the bla NDM-5-carrying plasmid, but the transferability of the bla NDM-1-positive plasmid was greater than that of the bla NDM-5-positive plasmid. In conclusion, the transmission of bla NDM-1 or bla NDM-5 is mainly disseminated by plasmids rather than clonal spread. The high transfer frequency of the IncX3 plasmid facilitates the prevalence and dissemination of NDM-KP among Enterobacteriaceae. IMPORTANCE The emergence of NDM-producing Klebsiella pneumoniae is a severe challenge to public health. The widespread presence of bla NDM-1 and bla NDM-5 in Enterobacteriaceae has aroused broad concern. In this study, we performed molecular characterization of bla NDM-1-carrying and bla NDM-5-harboring IncX3-type plasmids in carbapenem-resistant Klebsiella pneumoniae (CRKP) and compared their phenotypes between strains with different bla NDM subtype. Our findings highlight the importance of IncX3-type plasmids in the transfer of the bla NDM-1 and bla NDM-5 genes and demonstrate that the bla NDM-1 plasmid possesses higher transfer ability. These data will provide important insights into carbapenem resistance gene transfer via plasmids and their further spread in clinical settings.

Clonal outbreak of NDM-1-producing Enterobacter hormaechei belonging to high-risk international clone ST78 with the coexistence of tmexCD2-toprJ2 and mcr-9 in China.

OBJECTIVES: The emergence of carbapenem-resistant Enterobacter cloacae complex (CR-ECC) has posed significant global challenges to the clinical treatment of healthcare-associated infections. This study reports the clonal outbreak of NDM-1-producing Enterobacter hormaechei (E. hormaechei) with the coexistence of tmexCD2-toprJ2 and mcr-9 in China. METHODS: During the outbreak (January 2018 - December 2021), 15 non-repetitive multidrug-resistant E. hormaechei strains were obtained from 13 patients in a tertiary hospital. Antimicrobial susceptibility testing, plasmid stability, plasmid conjugation, plasmid fitness evaluation, colistin induction, whole-genome sequencing, and bioinformatics analysis were performed. A phylogenetic tree was constructed based on single nucleotide polymorphisms of core genomes to illustrate the evolutionary dynamics of mcr-9-carrying E. hormaechei strains worldwide. RESULTS: The 15 E. hormaechei strains belonged to the high-risk international clone ST78 and co-harboured tmexCD2-toprJ2 and blaNDM-1, of which 12 E. hormaechei strains carried the mcr-9 gene. Whole-genome sequencing analysis revealed that tmexCD2-toprJ2 and blaNDM-1 coexisted on the IncFIB/IncFII-type plasmid, which could be transferred to Escherichia coli J53 by conjugation and had a significant effect on host fitness. The mcr-9 gene was located between two insertion sequences, IS903B and IS1R, but lacked the two-component system regulatory gene qseBC, which might be the reason for all mcr-9-positive E. hormaechei strains remaining susceptible to colistin. The expression of mcr-9 was not inducible in strains confirmed by colistin induction assays. Phylogenetic analysis illustrated the silent spread and rapid evolution of mcr-9-carrying E. hormaechei worldwide. CONCLUSION: This study enriched the epidemiological and genomic characterisation of the coexistence of tmexCD2-toprJ2 and mcr-9 in ST78 CR-ECC isolates and demonstrated that they could prolong clonal dissemination in a tertiary hospital in China. Continuous epidemiological surveillance and molecular characterisation of CR-ECC should be conducted to monitor the evolution of CR-ECC around the world.

Smaller sulfur molecules promise better lithium-sulfur batteries.

The lithium-sulfur battery holds a high theoretical energy density, 4-5 times that of today's lithium-ion batteries, yet its applications have been hindered by poor electronic conductivity of the sulfur cathode and, most importantly, the rapid fading of its capacity due to the formation of soluble polysulfide intermediates (Li(2)S(n), n = 4-8). Despite numerous efforts concerning this issue, combatting sulfur loss remains one of the greatest challenges. Here we show that this problem can be effectively diminished by controlling the sulfur as smaller allotropes. Metastable small sulfur molecules of S(2-4) were synthesized in the confined space of a conductive microporous carbon matrix. The confined S(2-4) as a new cathode material can totally avoid the unfavorable transition between the commonly used large S(8) and S(4)(2-). Li-S batteries based on this concept exhibit unprecedented electrochemical behavior with high specific capacity, good cycling stability, and superior rate capability, which promise a practicable battery with high energy density for applications in portable electronics, electric vehicles, and large-scale energy storage systems.