Clone dissemination of IncX3 plasmid carrying bla(NDM-1) in ST76 carbapenem resistance Klebsiella pneumoniae and bactericidal efficiency of aztreonam combined with avibactam in vitro and in vivo.

The rapid spread of the New Delhi Metal-β-lactamase-1 (NDM-1) gene in Klebsiella pneumoniae poses a substantial challenge to pediatric therapeutic care. Here, we aimed to characterise the IncX3-type plasmid carrying the blaNDM-1 gene in ST76 carbapenem resistance K. pneumoniae (CRKP) strains and assess the in vitro and in vivo bactericidal efficacy of Aztreonam (ATM) combined with Avibactam (AVI) (ATM+AVI) against CRKP. The broth microdilution method and PCR were used to detect antimicrobial susceptibility and antibiotic resistance genes. Genetic relatedness was determined using Pulsed-Field Gel Electrophoresis (PFGE) and Multilocus Sequence Typing (MLST). The plasmid conjugation assay was used to verify the transmissibility of drug-resistant plasmids. Whole-Genome Sequencing (WGS) was employed to elucidate the genomic attributes of the genes. The Fractional Inhibitory Concentration (FIC) was calculated based on the checkerboard titration assay to determine the antimicrobial effect of ATM+AVI. The time-kill curve assay and a mouse anti-infection model were used to investigate the in vitro and in vivo bactericidal efficiency of ATM+AVI. Seven blaNDM-1-producing strains were found to be highly resistant to carbapenems, and they all belonged to the same sequence type (ST76) and were classified into the same PFGE clusters with an 89.1% similarity. The conjugation assay showed that the blaNDM-1-carrying plasmid was successfully transferred to Escherichia coli 600, resulting in transconjugants with carbapenem antibiotic resistance. A 54-kb IncX3 plasmid (pNDM-XZA88) carried the blaNDM-1 gene located on a Tn125 transposon-like element structure, demonstrating the transferability of resistance genes. Genome comparative analysis revealed that pNDM-XZA88 was highly similar to pCQ17 × 3 and pRor-30818cz and had relatively conserved backbones and variable accessory regions compared to the other four plasmids (pC39-334 kb, pNDM-1-DY1928, pNDM-K725, and pNDM-Z244). The checkerboard titration and time-kill curve assays revealed that the ATM+AVI combination therapy exerted significant bactericidal efficacy against the blaNDM-1-producing strains in vitro. The ATM+AVI combination also significantly reduced the bacterial burden in a mouse infection model constructed using the blaNDM-1-producing K. pneumoniae. This study demonstrated the clone dissemination of blaNDM-1-harboring IncX3 plasmids among the ST76 K. pneumoniae isolated from pediatric patients. Therefore, more attention should be paid to preventing this high-risk clone from harming pediatric patients. Moreover, we deduced that the ATM+AVI combination therapy is an effective strategy for treating blaNDM-1-producing K. pneumoniae.

Huo T ，Kong Z ，Dong G ，Zhao S ，Liu X ，Jiang F ... -  《-》

Dissemination of the bla(NDM-5) Gene via IncX3-Type Plasmid among Enterobacteriaceae in Children.

The continuous emergence of novel New Delhi metallo-β-lactamase-5 (NDM-5)-producing Enterobacteriaceae isolates is receiving more and more public attention. Twenty-two NDM-5-producing strains were identified from 146 carbapenemase-producing Enterobacteriaceae (CRE) strains isolated from pediatric patients between January and March 2017, indicating that the blaNDM-5 gene has spread to children. All 22 isolates, including 16 Klebsiella pneumoniae strains, four Klebsiella aerogenes strains, and two Escherichia coli strains, showed significantly high resistance to β-lactam antibiotics (except aztreonam) but remained susceptible to tigecycline and colistin. K. pneumoniae and K. aerogenes strains were respectively defined as homologous clonal isolates by pulsed-field gel electrophoresis (PFGE). Multilocus sequence typing (MLST) results confirmed the genetic relatedness with all K. pneumoniae strains belonging to sequence type (ST) 48. Two E. coli isolates (ST617 and ST1236) were considered genetically unrelated. Twenty-two blaNDM-5 plasmids were positive for the IncX3 amplicon and showed almost identical profiles after digestion with HindIII and EcoRI. Four representative strains (K. pneumoniae K725, K. aerogenes CR33, E. coli Z214, and E. coli Z244) were selected for further study. Plasmids harboring blaNDM-5 showed strong stability in both clinical isolates and transconjugants, without apparent plasmid loss after 100 serial generations. S1-PFGE followed by Southern blot analysis demonstrated that the blaNDM-5 gene was located on an ∼46-kb plasmid. Plasmid sequences of pNDM-K725, pNDM-CR33, and pNDM-Z214 were almost identical but were slightly different from that of pNDM-Z244. Compared with pNDM-Z244, ΔISAba125 and partial copies of IS3000 were missing. The genetic backgrounds of the blaNDM-5 gene in four strains were slightly different from that of the typical pNDM_MGR194. This study comprehensively characterized the horizontal gene transfer of the blaNDM-5 gene among different Enterobacteriaceae isolates in pediatric patients, and the IncX3-type plasmid was responsible for the spread.IMPORTANCE The emergence of CRE strains resistant to multiple antibiotics is considered a substantial threat to human health. Therefore, all the efforts to provide a detailed molecular transmission mechanism of specific drug resistance can contribute positively to prevent the further spread of multidrug-resistant bacteria. Although the new superbug harboring blaNDM-5 has been reported in many countries, it was mostly identified among E. coli strains, and the gene transfer mechanism has not been fully recognized and studied. In this work, we identified 22 blaNDM-5-positive strains in different species of Enterobacteriaceae, including 16 Klebsiella pneumoniae strains, four Klebsiella aerogenes strains, and two Escherichia coli strains, which indicated the horizontal gene transfer of blaNDM-5 among Enterobacteriaceae strains in pediatric patients. Moreover, blaNDM-5 was located on a 46-kb IncX3 plasmid, which is possibly responsible for this widespread horizontal gene transfer. The different genetic contexts of the blaNDM-5 gene indicated some minor evolutions of the plasmid, based on the complete sequences of the blaNDM-5 plasmids. These findings are of great significance to understand the transmission mechanism of drug resistance genes, develop anti-infection treatment, and take effective infection control measures.

Tian D ，Wang B ，Zhang H ，Pan F ，Wang C ，Shi Y ，Sun Y ... -  《mSphere》

Dissemination and Stability of the bla(NDM-5)-Carrying IncX3-Type Plasmid among Multiclonal Klebsiella pneumoniae Isolates.

NDM-5 carbapenemase was mainly identified in Escherichia coli, while the rapid transmission of blaNDM-5 among Enterobacteriaceae has raised serious public attention. This study identified 14 NDM-5-producing Klebsiella pneumoniae isolates from 107 carbapenem-resistant K. pneumoniae isolates, recovered from blood, urine, and normally sterile body fluids of pediatric patients from January 2016 to December 2018. All NDM-5-producing isolates were highly resistant to β-lactams, while tigecycline and polymyxin B exhibited excellent antimicrobial activity. These 14 strains belonged to 9 different sequence types (STs) and displayed various pulsed-field gel electrophoresis (PFGE) patterns, suggesting that they were not clonally related. S1-PFGE followed by Southern blotting showed that the blaNDM-5 gene was located on an ∼46-kb IncX3 plasmid in all strains. All blaNDM-5-carrying plasmids were successfully transferred into recipient E. coli J53. PCR-based sequencing demonstrated that all of the blaNDM-5-carrying plasmids shared highly similar backbones, with nucleotide sequence identity of >99%. Moreover, this plasmid displayed high sequence similarity to the previously reported epidemic IncX3 blaNDM-5-carrying plasmids, with dynamic changes observed only in blaNDM-5-surrounding elements. Interestingly, the IncX3 blaNDM-5-carrying plasmids showed strong stability in clinical isolates when cultured in antibiotic-free medium. However, after the conjugation inhibitor linoleic acid was added, a gradual increase in the level of IncX3 plasmid loss could be observed. Clinical isolates displayed 10% to 15% blaNDM-5-carrying plasmid loss after coculture with linoleic acid for 5 days. These results showed that the IncX3 plasmid facilitated the dissemination of blaNDM-5 among multiclonal K. pneumoniae strains in children and that conjugal transfer contributed significantly to IncX3 plasmid stability within K. pneumoniaeIMPORTANCE The emergence and spread of New Delhi metallo-β-lactamase (NDM)-producing Enterobacteriaceae have been a serious challenge to public health, and NDM-5 shows increased resistance to carbapenems compared with other variants. NDM-5 has been identified mostly in E. coli but has rarely been described in K. pneumoniae and other Enterobacteriaceae isolates. Here, we present the dissemination of highly similar 46-kb IncX3 blaNDM-5-carrying plasmids among multiclonal K. pneumoniae strains in children, highlighting the horizontal gene transfer of blaNDM-5 among K. pneumoniae strains via the IncX3 plasmid. Moreover, the IncX3 blaNDM-5-carrying plasmids displayed strong stability in clinical strains when cultured in antibiotic-free medium, and the plasmid maintenance was attributed partly to conjugal transfer. Plasmid conjugation is mediated by the type IV secretion system (T4SS), and T4SS is conserved among all epidemic IncX3 blaNDM-5-carrying plasmids. Therefore, combining conjugation inhibition and promotion of plasmid loss would be an effective strategy to limit the conjugation-assisted persistence of IncX3 blaNDM-5-carrying plasmids.

Zhu W ，Wang X ，Qin J ，Liang W ，Shen Z ... -  《mSphere》

Dynamic evolution of ceftazidime-avibactam resistance from a single patient through the IncX3_NDM-5 plasmid transfer and bla(KPC) mutation.

The rapid dissemination of carbapenem-resistant Enterobacterales (CRE) especially carbapenem-resistant Klebsiella pneumoniae (CRKP) poses a great threat to global public health. Ceftazidime-avibactam, a novel β-lactam/β-lactamase inhibitor combination, has been widely used due to its excellent antibacterial activity against KPC-producing K. pneumoniae. However, several resistance mechanisms have been reported since its use. Here, we conducted a series of in vitro experiments to reveal and demonstrate the dynamic evolution of ceftazidime-avibactam resistance including interspecies IncX3_NDM-5 plasmid transfer between Enterobacter cloacae and K. pneumoniae and blaKPC mutation from blaKPC-2 to blaKPC-33. Through the analysis of conjugation frequency and fitness cost, the IncX3_NDM-5 plasmid in this study showed strong transmissibility and stability in E. coli EC600 and clinical strain K. pneumoniae 5298 as recipient strain. With increasing ceftazidime-avibactam concentration, the conjugation frequency remained at 10-3-10-5, while the mutation frequency of K. pneumoniae 5298 was 10-6-10-8 at the same concentration. Further plasmid analysis (the IncX3_NDM plasmid from this study and other 658 plasmids from the NCBI database) revealed the diverse origin and genetic structure of blaNDM-5 carrying plasmids. E. coli (42.9%), China (43.9%), IncX3 (66.6%) are the most common strains, regions, and Inc types respectively. By analysing of genetic environment detected in IncX3 plasmids, the dominant structures (168/258, 65.1%) were identified: ISKox3-IS26-blaNDM-5-IS5-ISAba125-Tn3000-Tn3. In additon, several structural variations were found in the core gene structure. In conclusion, the high fitness and transmissibility of the IncX3_NDM-5 plasmids were noteworthy. More importantly, the diverse ceftazidime-avibactam resistance mechanisms including blaNDM-5 tranfer and blaKPC-2 mutation highlighted the importance of the continuous monitoring of antimicrobial susceptibility and carbapenemases subtype during ceftazidime-avibactam treatment.

Tang C ，Shen S ，Yang W ，Shi Q ，Ding L ，Han R ，Hu F ... -  《-》

In vitro and in vivo bactericidal activity of ceftazidime-avibactam against Carbapenemase-producing Klebsiella pneumoniae.

Zhang W ，Guo Y ，Li J ，Zhang Y ，Yang Y ，Dong D ，Zhu D ，He P ，Hu F ... -  《Antimicrobial Resistance and Infection Control》