Characterization of an IMP-4-Producing Klebsiella pneumoniae ST1873 Strain Recovered from an Infant with a Bloodstream Infection in China

Characterization of pKPN945B, a novel transferable IncR plasmid from hypervirulent carbapenem-resistant Klebsiella pneumoniae, harboring blaIMP-4 and qnrS1

Carbapenem-resistant Klebsiella pneumoniae producing metallo-β-lactamase poses a major public health threat worldwide. Imipenemase often coexists with other resistance genes leading to the formation of multidrug-resistant bacteria. In this study, we describe the microbiological and genomic characteristics of the hypervirulent carbapenem-resistant K. pneumoniae ST20-K23 strain KPN945 harboring blaIMP-4 and qnrS1. The minimum inhibitory concentration of KPN945 against antimicrobials was determined by the broth microdilution method. The virulence of KPN945 was evaluated through string test, serum killing resistance, and Galleria mellonella larvae infection models. The transferability of pKPN945B was assessed using a conjugation test. The genome sequence characteristics of KPN945 were analyzed through whole genome sequencing, and a phylogenetic tree was constructed to evaluate the prevalence of imipenemase. Our findings showed that KPN945 was non-susceptible to β-lactam antibiotics, highly resistant to serum killing, and highly lethal to G. mellonella larvae. The fusion plasmid pKPN945B carried by the isolate KPN945 belonged to the IncR incompatibility group and harbored multiple drug resistance genes such as blaIMP-4, blaCTX-M-14, qnrS1, and sul2. The most important point is that the IncR plasmid is a novel plasmid that arose by the accretion of parts from different plasmids, making it transferable and with a fitness cost. Globally, blaIMP-4 is the most prevalent imipenemase subtype, with the highest isolation rates in Asia, particularly China. The spread of blaIMP-4, especially the emergence of transferable plasmids, deserves our vigilance and prevention. Additionally, we should pay attention to the formation of hypervirulent K. pneumoniae mediated by non-virulent plasmids.

IMPORTANCE

Up to now, IncR replicons carrying blaIMP-4 have not been reported, and the IncR plasmids described in previous studies have been found to be non-transferrable to other bacteria through conjugation. Moreover, there have been no extensive phylogenetic analyses of strains carrying blaIMP in the published papers. The lack of data in these studies is noteworthy because blaIMP appears in the novel transferable fusion plasmid IncR. Although the IncR plasmid has no tra operon, it can still be transferred to Escherichia coli EC600 or Klebsiella pneumoniae ATCC13883 (RIFR) without high fitness cost, but it only affects the MIC of imipenem. blaIMP integrates with other resistance mechanisms leading to the formation of multidrug-resistant strains. Notably, the high prevalence of blaIMP-4 in Asia and the presence of blaIMP-4 on novel transferable IncR plasmids suggest the urgent need to monitor the emergence of such plasmids and control their spread.

Whole-genome sequencing of clinical isolates of Klebsiella michiganensi in China carrying blaIPM-4 and blaNDM-1

AIM

This study aimed to analyze the prevalence, phenotypes, and carriage of resistance genes of carbapenem-resistant Klebsiella michiganensis strains isolated in our hospital.

METHOD

ology: Four K. michiganensis strains were collected from January 2015 to December 2023. Antimicrobial susceptibility was tested using 21 antibiotics with the BD Phoenix™ M50 System. Whole-genome sequencing of the four strains was performed on an Illumina NovaSeq 6000 platform. Species identification was performed using Kleborate software, sequence type (ST) was performed using MLST, and prediction of antibiotic resistance genes and virulence genes were performed using ABRicate. PlasmidFinder was used to search for plasmids. Whole genome data from 211 strains of carbapenem-resistant K. michiganensis were downloaded from the NCBI database; together with the strains in this study, these data were used to construct an phylogenetic tree using genome single nucleotide polymorphisms (SNP).

RESULTS

Antimicrobial susceptibility showed that K. michiganensis was highly resistant to β-lactams. For the three carbapenems, strain WF0046 was only resistant to ertapenem, while WF0047, WF0052, and WF0053 were resistant to all three carbapenems tested. The four strains of K. michiganensis only showed complete sensitivity to polymyxin E and tigecycline. The four K. michiganensis strains were found to have 43 resistance genes, and all carried carbapenem resistance genes; WF0046 carried the carbapenem resistance gene blaIMP-4, while the other three strains carried blaNDM-1. Among the other resistance genes, β-lactam resistance genes were predicted most (11 types), followed by eight types of aminoglycoside resistance genes. Of the strains characterized in this study, WF0046 belonged to ST158, WF0047 belonged to ST40, WF0052 belonged to ST533, and WF0053 belonged to ST13. These four strains, along with 211 carbapenem-resistant K. michiganensis strains downloaded from NCBI, were divided into five clades; WF0052 belonged to clade A, WF0046 belonged to clade C, and WF0047 and WF0053 both belonged to clade D. The four strains had relatively distant genetic relationships; WF0046, WF0047, and WF0053 were closely related to strains of human origin from other regions of China, while WF0052 was genetically close with a strain of K. michiganensis isolated in the United States.

CONCLUSION

The strains of K. michiganensis from our hospital were resistant to multiple antibiotics, and all strains carried carbapenem resistance genes along with multiple other antibiotic resistance genes. The phylogenetic results showed that these four strains had distant genetic relationships and different ST types, indicating that they came from different sources and the possibility of polyclonal transmission.

Mechanism for transmission and pathogenesis of carbapenem-resistant Enterobacterales harboring the carbapenemase IMP and clinical countermeasures

Carbapenem-resistant Enterobacterales (CRE) are some of the most important pathogens causing infections, which can be challenging to treat. We identified four blaIMP-carrying CRE isolates and collected clinical data. The transferability and stability of the plasmid were verified by conjugation, successive passaging, and plasmid elimination assays. The IncC blaIMP-4-carrying pIMP4-ECL42 plasmid was successfully transferred into the recipient strain, and the high expression of traD may have facilitated the conjugation transfer of the plasmid. Interestingly, the plasmid showed strong stability in clinical isolates. Whole-genome sequencing was performed on all isolates. We assessed the sequence similarity of blaIMP -harboring plasmid from our institution and compared it to plasmids for which sequence data are publicly available. We found that four blaIMP-carrying CRE belonged to four different sequence types. The checkerboard technique and time-kill assays were used to investigate the best antimicrobial therapies for blaIMP-carrying CRE. The time-kill assay showed that the imipenem of 1× minimum inhibitory concentration (MIC) alone had the bactericidal or bacteriostatic effect against IMP-producing strains at 4-12 h in vitro. Moreover, the combination of tigecycline (0.5/1/2 × MIC) and imipenem (0.5/1 × MIC) showed a bactericidal effect against the blaIMP-26-carrying CRECL60 strain.IMPORTANCECarbapenem-resistant Enterobacterales (CRE) are an urgent public health threat, and infections caused by these microorganisms are often associated with high mortality and limited treatment options. This study aimed to determine the clinical features, molecular characteristics, and plasmid transmissible mechanisms of blaIMP carriage as well as to provide a potential treatment option. Here, we demonstrated that conjugated transfer of the IncC blaIMP-4-carrying plasmid promotes plasmid stability, so inhibition of conjugated transfer and enhanced plasmid loss may be potential ways to suppress the persistence of this plasmid. The imipenem alone or tigecycline-imipenem combination showed a good bactericidal effect against IMP-producing strains. In particular, our study revealed that imipenem alone or tigecycline-imipenem combination may be a potential therapeutic option for patients who are infected with IMP-producing strains. Our study supports further trials of appropriate antibiotics to determine optimal treatment and emphasizes the importance of continued monitoring of IMP-producing strains in the future.

An IncN-ST7 epidemic plasmid mediates the dissemination of carbapenem-resistant Klebsiella pneumoniae in a neonatal intensive care unit in China over 10 years

OBJECTIVES

Carbapenem-resistant Klebsiella pneumoniae (CRKP) has widely disseminated globally, but its epidemiological characterization and clinical significance in paediatric patients are not well understood. In this study, we aimed to trace the dissemination dynamics of CRKP in the neonatal intensive care unit (NICU) of a tertiary hospital over a 10-y period.

METHODS

We collected 67 non-duplicate K. pneumoniae species complex isolates from the NICU with patient metadata during 2009-2018. Antimicrobial susceptibility was determined by the agar or broth microdilution method. Risk factors for CRKP-positive patients were identified by univariate and multivariate analysis. Genetic characterization was dissected by whole-genome sequencing. Plasmid transmissibility, stability, and fitness were assessed.

RESULTS

Thirty-four of 67 isolates (50.75%) were identified as CRKP. Premature rupture of membranes, gestational age, and invasive procedures are independent risk factors for CRKP-positive patients. The annual isolation rate of CRKP varied between 0% and 88.9%, and multiple clonal replacements were observed during the study period, which could be largely due to the division of the NICU. All but one CRKP produced IMP-4 carbapenemase, which was encoded by an IncN-ST7 epidemic plasmid, suggesting that the IncN-ST7 plasmid mediated the CRKP dissemination in the NICU over 10 y. The same plasmid was found in several CRKP isolates from adult patients, of which two ST17 isolates from the neurosurgery department shared a high homology with the ST17 isolates from the NICU, indicating possible cross-departmental transmission.

CONCLUSION

Our study highlights the urgent need for infection control measures targeting high-risk plasmids like IncN-ST7.

Antimicrobial Peptides: From Design to Clinical Application

Infection of multidrug-resistant (MDR) bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), carbapenem-resistant Enterobacteriaceae (CRE), and extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli, brings public health issues and causes economic burden. Pathogenic bacteria develop several methods to resist antibiotic killing or inhibition, such as mutation of antibiotic function sites, activation of drug efflux pumps, and enzyme-mediated drug degradation. Antibiotic resistance components can be transferred between bacteria by mobile genetic elements including plasmids, transposons, and integrons, as well as bacteriophages. The development of antibiotic resistance limits the treatment options for bacterial infection, especially for MDR bacteria. Therefore, novel or alternative antibacterial agents are urgently needed. Antimicrobial peptides (AMPs) display multiple killing mechanisms against bacterial infections, including directly bactericidal activity and immunomodulatory function, as potential alternatives to antibiotics. In this review, the development of antibiotic resistance, the killing mechanisms of AMPs, and especially, the design, optimization, and delivery of AMPs are reviewed. Strategies such as structural change, amino acid substitution, conjugation with cell-penetration peptide, terminal acetylation and amidation, and encapsulation with nanoparticles will improve the antimicrobial efficacy, reduce toxicity, and accomplish local delivery of AMPs. In addition, clinical trials in AMP studies or applications of AMPs within the last five years were summarized. Overall, AMPs display diverse mechanisms of action against infection of pathogenic bacteria, and future research studies and clinical investigations will accelerate AMP application.

Using Whole Genome Sequencing to Trace, Control and Characterize a Hospital Infection of IMP-4-Producing Klebsiella pneumoniae ST2253 in a Neonatal Unit in a Tertiary Hospital, China

Background: The purpose of this study is to use whole genome sequencing (WGS) combined with epidemiological data to track a hospital infection of the carbapenem-resistant Klebsiella pneumoniae (CRKP), which affected 3 neonatal patients in the neonatal intensive care unit (NICU). Methods: The minimum inhibitory concentrations for the antimicrobial agents were determined according to the guidelines of the Clinical and Laboratory Standards Institute. Beta-lactamases were investigated using the polymerase chain reaction and DNA sequencing. The transferability of the plasmid was investigated by a conjugation experiment. The clonal relationships were evaluated using multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE). WGS and single nucleotide polymorphisms (SNPs) analysis were performed on the CRKP isolates to investigate how the infection might progress. Results: Nine CRKP isolates were obtained from the NICU, seven from three patients, one from a duster cloth and one from the hand of a nurse, they all harbored blaIMP-4. Other resistance genes including blaKPC-2, blaIMP-4, blaSHV-1, blaTEM-1, blaCTX-M-15, and blaDHA-1 were also detected. PFGE analysis showed that IMP-4-producing K. pneumoniae were clonally related, and MLST assigned them to a new sequence type 2253. The SNP variations throughout the genome divided the 9 strains into three clades. Clade 1 comprised 7 strains (K1- K2 and K4-K8), whereas clade 2 and 3 consisted of only one strain each: K3 and K9, respectively.The sputum isolate K3 from patient 3 was the most distinct one differing from the other eight isolates by 239-275 SNPs. Conclusions: This is a report of using WGS to track a hospital infecion of IMP-4-producing K. pneumoniae ST2253 among neonates. Nosocomial surveillance systems are needed to limit the spread of the infection caused by these pathogens resulting from the environmental exposure in NICUs.

First Report of bla IMP-4 and bla SRT-2 Coproducing Serratia marcescens Clinical Isolate in China

Carbapenem-resistant Enterobacterales (CRE) has become a major therapeutic concern in clinical settings, and carbapenemase genes have been widely reported in various bacteria. In Serratia marcescens, class A group carbapenemases including SME and KPC were mostly identified. However, there are few reports of metallo-β-lactamase-producing S. marcescens. Here, we isolated a carbapenem-resistant S. marcescens (S378) from a patient with asymptomatic urinary tract infection which was then identified as an IMP-4-producing S. marcescens at a tertiary hospital in Sichuan Province in southwest of China. The species were identified using MALDI-TOF MS, and carbapenemase-encoding genes were detected using PCR and DNA sequencing. The results of antimicrobial susceptibility testing by broth microdilution method indicated that the isolate S. marcescens S378 was resistant to meropenem (MIC = 32 μg/ml) and imipenem (MIC = 64 μg/ml) and intermediate to aztreonam (MIC = 8 μg/ml). The complete genomic sequence of S. marcescens was identified using Illumina (Illumina, San Diego, CA, United States) short-read sequencing (150 bp paired-end reads); five resistance genes had been identified, including bla_IMP–4, bla_SRT–2, aac(6′)-Ic, qnrS1, and tet(41). Conjugation experiments indicated that the bla_IMP–4-carrying plasmid pS378P was conjugative. Complete sequence analysis of the plasmid pS378P bearing bla_IMP–4 revealed that it was a 48,780-bp IncN-type plasmid with an average GC content of 50% and was nearly identical to pP378-IMP (99% nucleotide identity and query coverage).

IncN1 ST7 Epidemic Plasmid Carrying blaIMP-4 in One ST85-Type Klebsiella oxytoca Clinical Isolate with Porin Deficiency

Purpose

Klebsiella oxytoca is an opportunistic pathogen causing nosocomial infections. This study was designed to characterize the genomic features of a carbapenem-resistant K. oxytoca strain and analyze its molecular characteristics.

Materials and Methods

The strain wzx-IMP was isolated from the blood of a 2-year-old girl diagnosed with acute myeloid leukemia-M7. Species identification was performed, and the minimal inhibitory concentration of the strain was measured. Multilocus sequence typing was performed to identify the subtypes of K. oxytoca. The transfer capacity of the blaIMP-4-harboring plasmid was investigated by conjugation experiments, and the genome characteristics of the strain were examined using whole-genome sequencing.

Results

wzx-IMP belongs to the ST85 type and is resistant to imipenem and meropenem, which harbored the blaIMP-4 gene. The blaIMP-4 gene was located in an IS26-associated class 1 integron of pwzx_IMP, which contains conserved IncN1-type backbone regions with a replication gene and its accessory structure for plasmid replication. The blaIMP-4-carrying plasmid in wzx-IMP was successfully transferred to Escherichia coli EC600 by conjugation. Whole-genome sequencing showed that the wzx-IMP isolate included the blaOXY-1-1 gene, accompanied by OmpK36 absence.

Conclusion

We report an ST85-type carbapenem-resistant K. oxytoca strain, which produces blaIMP-4 located in an IncN1-type plasmid and accompanied by OmpK36 porin deficiency.

A case report of pyogenic liver abscess caused by hypervirulent Klebsiella pneumoniae diagnosed by metagenomic next-generation sequencing

A 56-year-old woman with a history of diabetes mellitus presented with high fever but no abdominal pain. An abdominal computed tomography scan showed a large liver abscess. Hypervirulent, string test-positive, rmpA/ampA2-, and iutA-positive Klebsiella pneumoniae was rapidly identified from drainage fluid of the liver abscess using metagenomic next-generation sequencing (mNGS). After intravenous antibiotic therapy and drainage of the abscess, the patient’s condition resolved. This case report highlights the value of mNGS in rapidly and accurately identifying a pathogenic microorganism, which helps reduce the incidence of antimicrobial resistance and enables the targeted use of antibiotics.

Risk factors for, and molecular epidemiology and clinical outcomes of, carbapenem- and polymyxin-resistant Gram-negative bacterial infections in pregnant women, infants, and toddlers: a systematic review and meta-analyses

In the following systematic review and meta-analyses, we report several conclusions about resistance to carbapenem and polymyxin last-resort antibiotics for treating multidrug-resistant bacterial infections among pregnant women and infants. Resistance to carbapenems and polymyxins is increasing, even in otherwise vulnerable groups such as pregnant women, toddlers, and infants, for whom therapeutic options are limited. In almost all countries, carbapenem-/polymyxin-resistant Klebsiella pneumoniae, Escherichia coli, and Acinetobacter baumannii infect and/or colonize neonates and pregnant women, causing periodic outbreaks with very high infant mortalities. Downregulation of plasmid-borne bla_NDM , bla_KPC , bla_OXA-48 , bla_IMP, bla_VIM , bla_GES-5 , and ompK35/36 in clonal strains accelerates the horizontal and vertical transmissions of carbapenem resistance among these pathogens. New Delhi metallo-β-lactamase (NDM)-positive isolates in infants/neonates have been mainly detected in China and India, while OXA-48-positive isolates in infants/neonates have been mainly detected in Africa. NDM-positive isolates in pregnant women have been found only in Madagascar. Antibiotic therapy, prolonged hospitalization, invasive procedures, mechanical ventilation, low birth weight, and preterm delivery have been common risk factors associated with carbapenem/polymyxin resistance. The use of polymyxins to treat carbapenem-resistant infections may be selecting for resistance to both agents, restricting therapeutic options for infected infants and pregnant women. Currently, low- and middle-income countries have the highest burden of these pathogens. Antibiotic stewardship, periodic rectal and vaginal screening, and strict infection control practices in neonatal ICUs are necessary to forestall future outbreaks and deaths.