New Delhi Metallo-β-Lactamase-Producing Enterobacterales Bacteria, Switzerland, 2019-2020

Molecular Epidemiology and In-Depth Characterization of Klebsiella pneumoniae Clinical Isolates from Armenia

The global dissemination of Klebsiella pneumoniae pathotypes with multidrug-resistant (MDR) and hypervirulent traits poses a threat to public health. The situation in Armenia is unclear, and we performed a comprehensive characterisation of 48 clinical isolates of K. pneumoniae, collected from 2018 to 2024. The majority of the isolates (64.58%) were extensively drug-resistant (XDR) and MDR. Genomic analysis of 21 isolates revealed the presence of international high-risk MDR clones (ST395, ST15, and ST307). The ST395 strains were isolated from children and resisted the first-line drugs such as beta-lactams. These isolates harboured a range of virulence determinants, from capsule polysaccharides to siderophores to regulators of the mucoid phenotype. The ST395 strains are enriched by ICEs, plasmids, and prophages, on which antimicrobial resistance (AMR) and virulence genes are located and which may lead to the convergence of MDR and hypervirulent traits. There is a widespread non-specific AMR mechanism among our K. pneumoniae strains. These are mutations in the porin genes, which reduce permeability to antimicrobials, and mutations in the regulators of efflux pumps, which lead to overexpression of drug efflux pumps such as AcrAB. These mechanisms may contribute to the elevated MICs and confer AMR to strains with no specific AMR genes.

Emergence of high-level aztreonam-avibactam and cefiderocol resistance following treatment of an NDM-producing Escherichia coli bloodstream isolate exhibiting reduced susceptibility to both agents at baseline

Background

Cefiderocol (FDC) or ceftazidime-avibactam with aztreonam (CZA-ATM) are frontline agents for New Delhi metallo-β-lactamase (NDM)-producing Enterobacterales; however, clinical data are scarce, and mechanisms of treatment-emergent resistance are ill-defined. Our objectives were to characterize serial isolates and stool microbiota from a liver transplant recipient with NDM-producing Escherichia coli bacteraemia.

Methods

Isolates collected pre- and post-CZA-ATM treatment underwent broth microdilution susceptibility testing and whole-genome sequencing. Longitudinal stool collected during CZA-ATM therapy underwent metagenomic sequencing (Nanopore MinION).

Results

The baseline isolate exhibited elevated MICs for ATM-AVI (16/4 µg/mL) and FDC (8 µg/mL). Posttreatment, a rectal surveillance isolate exhibited high-level resistance to ATM-AVI (> 128/4 µg/mL) and FDC (32 µg/mL). Both isolates belonged to ST361 and harboured WT bla NDM-5. The baseline isolate contained wild type (WT) bla CMY-145 and mutations in ftsI (which encodes PBP3), including a YRIN insertion at residue 338 and the non-synonymous substitutions Q227H, E353K and I536L. The posttreatment isolate harboured new mutations in ftsI (A417 V) and bla CMY-145 (L139R and N366Y). Analysis of four stool samples collected during CZA-ATM treatment revealed high E. coli abundance. E. coli relative abundance increased from 34.5% (first sample) to 61.9% (last sample).

Conclusions

Baseline mutations in ftsI were associated with reduced susceptibility to ATM-AVI and FDC in an ST361 NDM-5-producing E. coli bloodstream isolate. High-level resistance was selected after CZA-ATM treatment, resulting in new ftsl and bla CMY-145 mutations. These findings underscore the need for ATM-AVI susceptibility testing for NDM producers, and the potential for PBP3 mutations to confer cross-resistance to ATM-AVI and FDC, which can emerge after CZA-ATM treatment.

Characterisation of a novel AmpC beta-lactamase, DHA-33, resistant to inhibition by cloxacillin

Plasmid-encoded DHA-type AmpCs have been extensively reported in Enterobacterales. The expression of the genes encoding these plasmid-mediated enzymes are inducible and these enzymes are capable of conferring resistance to a wide spectrum of beta-lactams including penicillins and broad-spectrum cephalosporins. The identification of infections caused by AmpC-producing bacteria is a necessity, both for infection control/epidemiology purposes and to inform treatment choices. A common testing method for AmpC production in the clinical laboratory setting is to supplement Mueller-Hinton agar plates used for antibiotic disk diffusion with cloxacillin, a potent inhibitor of AmpC enzymes. Here we describe a novel DHA variant, produced by a clinical Escherichia coli isolate, which is resistant to cloxacillin inhibition.

Clinical Features and Outcomes of Infections Caused by Metallo-β-Lactamase-Producing Enterobacterales: A 3-Year Prospective Study From an Endemic Area

BACKGROUND

Metallo-β-lactamase (MBL)-producing Enterobacterales are increasing worldwide. Our aim was to describe clinical features, treatments, and outcomes of infections by MBL-Enterobacterales.

METHODS

A prospective observational study conducted in the Pisa University Hospital (January 2019 to October 2022) included patients with MBL-producing Enterobacterales infections. The primary outcome measure was the 30-day mortality rate. Multivariable Cox regression analysis was performed to identify factors associated with that mortality rate, and adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs) were calculated.

RESULTS

The study's 343 patients included 15 with Verona integron-encoded MBL (VIM)- and 328 with New Delhi MBL (NDM)-producing Enterobacterales infections; there were 199 patients (58%) with bloodstream infections, 60 (17.5%) with hospital-acquired or ventilator-associated pneumonia, 60 (17.5%) with complicated urinary tract infections, 13 (3.8%) with intra-abdominal infections, and 11 (3.2%) with skin and soft-tissue infections. The 30-day mortality rate was 29.7%. Of 343 patients, 32 did not receive in vitro active antibiotic therapy, 215 (62.7%) received ceftazidime-avibactam plus aztreonam, 33 (9.6%) received cefiderocol-containing regimens, 26 (7.6%) received colistin-containing regimens, and 37 (10.8%) received other active antibiotics. On multivariable analysis, septic shock (aHR, 3.57 [95% CI, 2.05-6.23]; P < .001) and age (1.05 [1.03-1.08]; P < .001) were independently associated with the 30-day mortality rate, while in vitro active antibiotic therapy within 48 hours after infection (0.48 [.26-.8]; P = .007) and source control (0.43 [.26-.72]; P = .001) were protective factors. Sensitivity analysis showed that ceftazidime-avibactam plus aztreonam, compared with colistin, was independently associated with a reduced 30-day mortality rate (aHR, 0.39 [95% CI, .18-.86]; P = .02). Propensity score analyses confirmed these findings.

CONCLUSIONS

MBL-producing carbapenem-resistant Enterobacterales infections are associated with high 30-day mortality rates. Patients with MBL-producing Enterobacterales infections should receive early active antibiotic therapy.

Risk Factors and Outcomes of Patients Colonized with KPC and NDM Carbapenemase-Producing Enterobacterales

Carbapenemase-producing enterobacterales (CPE) poses an increasing threat in hospitals worldwide. Recently, the prevalence of different carbapenemases conferring carbapenem resistance in enterobacterales changed in our country, including an increase in New Delhi Metallo-beta-lactamase (NDM)-CPE. We conducted a comparative historical study of adult patients colonized with Klebsiella pneumoniae carbapenemase (KPC)-CPE (July 2016 to June 2018, a historical cohort) vs. NDM-CPE (July 2016 to January 2023). We identified patients retrospectively through the microbiology laboratory and reviewed their files, extracting demographics, underlying diseases, Charlson Comorbidity Index (CCI) scores, treatments, and outcomes. This study included 228 consecutive patients from whom a CPE rectal swab screening was obtained: 136 NDM-CPE positive and 92 KPC-CPE positive. NDM-CPE-colonized patients had a shorter hospitalization length and a significantly lower 30-day post-discharge mortality rate (p = 0.002) than KPC-CPE-colonized patients. Based on multivariate regression, independent risk factors predicting CPE-NDM colonization included admission from home and CCI < 4 (p < 0.001, p = 0.037, respectively). The increase in NDM-CPE prevalence necessitates a modified CPE screening strategy upon hospital admission tailored to the changing local CPE epidemiology. In our region, the screening of younger patients residing at home with fewer comorbidities should be considered, regardless of a prior community healthcare contact or hospital admission.

Discovery of 2-Aminothiazole-4-carboxylic Acids as Broad-Spectrum Metallo-β-lactamase Inhibitors by Mimicking Carbapenem Hydrolysate Binding

Metallo-β-lactamases (MBLs) are zinc-dependent enzymes capable of hydrolyzing all bicyclic β-lactam antibiotics, posing a great threat to public health. However, there are currently no clinically approved MBL inhibitors. Despite variations in their active sites, MBLs share a common catalytic mechanism with carbapenems, forming similar reaction species and hydrolysates. We here report the development of 2-aminothiazole-4-carboxylic acids (AtCs) as broad-spectrum MBL inhibitors by mimicking the anchor pharmacophore features of carbapenem hydrolysate binding. Several AtCs manifested potent activity against B1, B2, and B3 MBLs. Crystallographic analyses revealed a common binding mode of AtCs with B1, B2, and B3 MBLs, resembling binding observed in the MBL-carbapenem product complexes. AtCs restored Meropenem activity against MBL-producing isolates. In the murine sepsis model, AtCs exhibited favorable synergistic efficacy with Meropenem, along with acceptable pharmacokinetics and safety profiles. This work offers promising lead compounds and a structural basis for the development of potential drug candidates to combat MBL-mediated antimicrobial resistance.

Efficacy of ceftazidime-avibactam, meropenem-vaborbactam, and imipenem-relebactam combinations against carbapenemase-producing Enterobacterales in Switzerland

Carbapenemase-producing in Enterobacterales (CPE) represent a critical health concern worldwide, including in Switzerland, leading to very limited therapeutic options. Therefore, our aim was to evaluate the susceptibility to the novel ß-lactam/ß-lactamase inhibitor combinations ceftazidime-avibactam, meropenem-vaborbactam, and imipenem-relebactam of CPE isolates recovered in Switzerland from 2018 to 2020. A total of 150 clinical CPE were studied including mainly Klebsiella pneumoniae (n = 61, 40.3%) and Escherichia coli (n = 53, 35.3%). The distribution of carbapenemases was as follows: KPC-like (32%), OXA-48-like (32%), NDM-like (24%), combinations of carbapenemases (10%), VIM-1 producers (n = 2), and a single IMI-1 producer. Overall, 77% of the strains were susceptible to meropenem-vaborbactam, 63% was susceptible to ceftazidime-avibactam, and 62% susceptible to imipenem-relebactam. Those data may contribute to optimize the choice of first line therapy for treating infections due to CPE.

An NDM-Producing Escherichia coli Clinical Isolate Exhibiting Resistance to Cefiderocol and the Combination of Ceftazidime-Avibactam and Aztreonam: Another Step Toward Pan-β-Lactam Resistance

Background

Cefiderocol and ceftazidime-avibactam plus aztreonam (CZA-ATM) are preferred treatment regimens for New Delhi metallo-β-lactamase (NDM)-producing infections.

Methods

We report the case of a US patient who traveled to India to receive a renal transplant. He subsequently experienced pyelonephritis by an NDM-producing Escherichia coli. Broth microdilution and the broth disk elution method indicated resistance to all β-lactams, including cefiderocol and CZA-ATM. Whole-genome sequencing investigations were undertaken to identify resistance mechanisms.

Results

An E. coli isolate belonging to sequence type (ST) 167 containing a bla_NDM-5 gene was identified on a plasmid of the IncFIA/IncFIB/IncFIC replicon groups. When compared with the genome of another ST167 E. coli clinical isolate containing bla_NDM-5 and exhibiting susceptibility to cefiderocol and CZA-ATM, a 12-base pair insertion in ftsI, translating to a 4-amino acid duplication in PBP3, was identified. Moreover, a bla_CMY-59 gene was harbored on an IncI-γ replicon type, and frameshift mutations were identified in the cirA iron transport gene.

Conclusions

This is the first clinical case of a US patient harboring an NDM-producing isolate exhibiting resistance to all available β-lactam agents. The isolate's unexpected resistance to cefiderocol and CZA-ATM was likely due to a combination of (1) a modified PBP3 (increased MICs to both regimens), (2) truncated iron-binding protein (increased cefiderocol MIC), and (3) a bla_CMY gene (reduced CZA-ATM activity). E. coli ST167 clinical isolates harboring bla_NDM-5 genes are a recognized international high-risk clone. When coupled with the additional mechanisms identified in our patient's isolate, which is not uncommon for this high-risk clone, pan-β-lactam resistance may occur.

Mortality Attributable to Bloodstream Infections Caused by Different Carbapenem-Resistant Gram-Negative Bacilli: Results From a Nationwide Study in Italy (ALARICO Network)

BACKGROUND

Our aim was to analyze mortality attributable to carbapenem-resistant (CR) gram-negative bacilli (GNB) in patients with bloodstream infections (BSIs).

METHODS

Prospective multicentric study including patients with GNB-BSI from 19 Italian hospitals (June 2018-January 2020). Patients were followed-up to 30 days. Primary outcomes were 30-day mortality and attributable mortality. Attributable mortality was calculated in the following groups: Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacterales, metallo-β-lactamases (MBL)-producing Enterobacterales, CR-Pseudomonas aeruginosa (CRPA), CR-Acinetobacter baumannii (CRAB). A multivariable analysis with hospital fixed-effect was built to identify factors associated with 30-day mortality. Adjusted OR (aORs) were reported. Attributable mortality was calculated according to the DRIVE-AB Consortium.

RESULTS

Overall, 1276 patients with monomicrobial GNB BSI were included: 723/1276 (56.7%) carbapenem-susceptible (CS)-GNB, 304/1276 (23.8%) KPC-, 77/1276 (6%) MBL-producing CRE, 61/1276 (4.8%) CRPA, and 111/1276 (8.7%) CRAB BSI. Thirty-day mortality in patients with CS-GNB BSI was 13.7% compared to 26.6%, 36.4%, 32.8% and 43.2% in patients with BSI by KPC-CRE, MBL-CRE, CRPA and CRAB, respectively (P < .001). On multivariable analysis, age, ward of hospitalization, SOFA score, and Charlson Index were factors associated with 30-day mortality, while urinary source of infection and early appropriate therapy resulted protective factors. Compared to CS-GNB, MBL-producing CRE (aOR 5.86, 95% CI 2.72-12.76), CRPA (aOR 1.99, 95% CI 1.48-5.95) and CRAB (aOR 2.65, 95% CI 1.52-4.61) were significantly associated with 30-day mortality. Attributable mortality rates were 5% for KPC-, 35% for MBL, 19% for CRPA, and 16% for CRAB.

CONCLUSIONS

In patients with BSIs, carbapenem-resistance is associated with an excess of mortality, with MBL-producing CRE carrying the highest risk of death.

Transferable IncX3 plasmid harboring blaNDM-1, bleMBL, and aph(3')-VI genes from Klebsiella pneumoniae conferring phenotypic carbapenem resistance in E. coli

BACKGROUND

The dissemination of carbapenem resistance via carbapenemases, such as the metallo-β-lactamase NDM, among Enterobacterales poses a public health threat. The aim of this study was to characterize a plasmid carrying the blaNDM-1 gene, which was extracted from a clinical Klebsiella pneumoniae uropathogen from an Egyptian patient suffering from a urinary tract infection.

METHODS AND RESULTS

The recovered plasmid was transformed into competent E. coli DH5α which acquired phenotypic resistance to cefoxitin, ceftazidime, and ampicillin/sulbactam, and intermediate sensitivity to ceftriaxone and imipenem (a carbapenem). Whole plasmid sequencing was performed on the extracted plasmid using the DNBSEQ™ platform. The obtained forward and reverse reads were assembled into contigs using the PRINSEQ and PLACNETw web tools. The obtained contigs were uploaded to PlasmidFinder and ResFinder for in silico plasmid typing and detection of antimicrobial resistance genes, respectively. The final consensus sequence was obtained using the Staden Package software. The plasmid (pNDMKP37, NCBI accession OK623716.1) was typed as an IncX3 plasmid with a size of 46,160 bp and harbored the antibiotic resistance genes blaNDM-1, bleMBL, and aph(3')-VI. The plasmid also carried mobile genetic elements involved in the dissemination of antimicrobial resistance including insertion sequences IS30, IS630, and IS26.

CONCLUSIONS

This is Egypt's first report of a transmissible plasmid co-harboring blaNDM-1 and aph(3')-VI genes. Moreover, the respective plasmid is of great medical concern as it has caused the horizontal transmission of multidrug-resistant phenotypes to the transformant. Therefore, new guidelines should be implemented for the rational use of broad-spectrum antibiotics, particularly carbapenems.

Molecular surveillance reveals the emergence and dissemination of NDM-5-producing Escherichia coli high-risk clones in Germany, 2013 to 2019

BackgroundCarbapenemase-producing Enterobacterales (CPE) are rapidly increasing worldwide, also in Europe. Although prevalence of CPE in Germany is comparatively low, the National Reference Centre for Multidrug-resistant Gram-negative Bacteria noted annually increasing numbers of NDM-5-producing Escherichia coli isolates.AimAs part of our ongoing surveillance programme, we characterised NDM-5-producing E. coli isolates received between 2013 and 2019 using whole genome sequencing (WGS).MethodsFrom 329 identified NDM-5-producing E. coli, 224 isolates from known geographical locations were subjected to Illumina WGS. Analyses of 222 sequenced isolates included multilocus sequence typing (MLST), core genome (cg)MLST and single-nucleotide polymorphism (SNP)-based analyses.ResultsResults of cgMLST revealed genetically distinct clusters for many of the 43 detected sequence types (ST), of which ST167, ST410, ST405 and ST361 predominated. The SNP-based phylogenetic analyses combined with geographical information identified sporadic cases of nosocomial transmission on a small spatial scale. However, we identified large clusters corresponding to clonal dissemination of ST167, ST410, ST405 and ST361 strains in consecutive years in different regions in Germany.ConclusionOccurrence of NDM-5-producing E. coli rose in Germany, which was to a large extent due to the increased prevalence of isolates belonging to the international high-risk clones ST167, ST410, ST405 and ST361. Of particular concern is the supra-regional dissemination of these epidemic clones. Available information suggest community spread of NDM-5-producing E. coli in Germany, highlighting the importance of epidemiological investigation and an integrated surveillance system in the One Health framework.

NDM-35-Producing ST167 Escherichia coli Highly Resistant to β-Lactams Including Cefiderocol

A multidrug-resistant (carbapenems, aztreonam + avibactam, and cefiderocol) ST167 Escherichia coli clinical isolate recovered from a patient hospitalized in Switzerland produced NDM-35 showing ca. 10-fold increased hydrolytic activity toward cefiderocol compared to NDM-1. The isolate co-produced a CMY-type β-lactamase, exhibited a four amino-acid insertion in PBP3, and possessed a truncated iron transporter CirA protein. Our study identified an association of unrelated resistance mechanisms leading to resistance to virtually all β-lactams in a high-risk E. coli clone.

A case–control study of infections caused by Klebsiella pneumoniae producing New Delhi metallo-beta-lactamase-1: Predictors and outcomes

Introduction

Infections caused by antimicrobial-resistant bacteria are a significant cause of death worldwide, and carbapenemase-producing bacteria are the principal agents. New Delhi metallo-beta-lactamase-1 producing Klebsiella pneumoniae (KP-NDM-1) is an extensively drug-resistant bacterium that has been previously reported in Mexico. Our aim was to conduct a case–control study to describe the risk factors associated with nosocomial infections caused by K. pneumoniae producing NDM-1 in a tertiary-care hospital in Mexico.

Methods

A retrospective case–control study with patients hospitalized from January 2012 to February 2018 at the Hospital Civil de Guadalajara “Fray Antonio Alcalde” was designed. During this period, 139 patients with a culture that was positive for K. pneumoniae NDM-1 (cases) and 486 patients hospitalized in the same department and on the same date as the cases (controls) were included. Data were analyzed using SPSS v. 24, and logistic regression analysis was conducted to calculate the risk factors for KP-NDM-1 infection.

Results

One hundred and thirty-nine case patients with a KP-NDM-1 isolate and 486 control patients were analyzed. In the case group, acute renal failure was a significant comorbidity, hospitalization days were extended, and significantly more deaths occurred. In a multivariate analysis of risk factors, the independent variables included the previous use of antibiotics (odds ratio, OR = 12.252), the use of a urinary catheter (OR = 5.985), the use of a central venous catheter (OR = 5.518), the use of mechanical ventilation (OR = 3.459), and the length of intensive care unit (ICU) stay (OR = 2.334) as predictors of infection with NDM-1 K. pneumoniae.

Conclusion

In this study, the previous use of antibiotics, the use of a urinary catheter, the use of a central venous catheter, the use of mechanical ventilation, and ICU stay were shown to be predictors of infection with NDM-1 K. pneumoniae and were independent risk factors for infection with NDM-1 K. pneumoniae.

A Retrospective Study of Risk Factors, Mortality, and Treatment Outcomes for Infections with Carbapenemase-Producing Enterobacterales in a Tertiary Hospital in Havana, Cuba

(1) Background: The spread of carbapenem-resistant Enterobacterales in hospitals constitutes an important epidemiological and therapeutic problem that especially affects vulnerable patients such as perioperative patients. (2) Methods: We conducted a descriptive, observational, retrospective case-control study of patients infected with carbapenemase-producing carbapenem-resistant Enterobacterales (CP-CRE) and carbapenem-susceptible Enterobacterales during the perioperative period in a tertiary hospital. (3) Results: Metallo-β-lactamase was detected in all 124 CRE isolates, with NDM-type carbapenemase being dominant, while 3 isolates coproduced KPC-type enzyme and showed high resistance rates against all antibiotics except colistin (25.2%). By analyzing the risk factors for infection, steroid use (OR: 3.22, p < 0.01), prior use of two or more antibiotics (OR: 4.04, p = 0.01), prior use of broad-spectrum cephalosporins (OR: 2.40, p = 0.04), and prior use of carbapenem (OR: 4.77, p = 0.03) were found to be independent risk factors for CP-CRE infection. In addition, in this study, we observed that the clinical outcomes of bloodstream infections and pneumonia associated with CP-CRE posed higher mortality risks. However, by analyzing the associations between treatment options and mortality, it was found that, in bloodstream infections caused by CP-CRE, colistin-based regimens showed a significant advantage (PR = 0.40, p = 0.03). (4) Conclusions: High mortality is associated with nosocomial infections in the perioperative period caused by carbapenemase-producing Enterobacterales, the dissemination of which in health care settings in Cuba remains a public health challenge.

Multicenter Study of Carbapenemase-Producing Enterobacterales in Havana, Cuba, 2016–2021

Surveillance of carbapenem resistance is particularly important for Enterobacterales, mainly in countries with limited healthcare resources. We conducted a cross-sectional study to detect carbapenem-resistant Enterobacterales at 10 sentinel hospitals in Havana, Cuba for a six year-period (2016–2021) by the National Reference Laboratory for Health Care-Associated Infections in the Pedro Kourí Institute. A total of 152 isolates were collected with phenotypic production of metallo-β-lactamase. NDM-type carbapenemase was detected in all the 152 isolates, and KPC-type enzyme gene was simultaneously identified in four NDM-positive isolates. The most abundant carbapenemase-producing Enterobacterales (CPE) species was Klebsiella pneumoniae (69.7%), followed by Enterobacter cloacae complex (13.2%), and Escherichia coli (5.9%). Over the study period, among CPE, prevalence of K. pneumoniae was almost constant, while Enterobacter spp. showed slightly increasing tendency. The urinary tract (36.2%) was the most prevalent source of infection with CPE, followed by bloodstream (26.3%) and surgical wound (17.1%), being frequently derived from Intensive Care Units (35.5%) and urology wards (21.7%). This study revealed the present situation of CPE in hospitals in Havana, Cuba, showing the emergence and dissemination of Enterobacterales producing NDM-type carbapenemase, mainly K. pneumoniae.

Differences in the Distribution of Species, Carbapenemases, Sequence Types, Antimicrobial Heteroresistance and Mortality Rates Between Pediatric and Adult Carbapenemase-Producing Enterobacterales in Bloodstream Infections

The dissemination of carbapenemase-producing Enterobacterales (CPE) is worrisome given their scarce treatment options. CPE bloodstream infections (BSIs) had a high mortality rate in adults, and there was little data on pediatric CPE-BSIs around the world. We comprehensively explored the differences in the clinical and microbiological characteristics between pediatric and adult CPE-BSIs. Forty-eight pediatric and 78 adult CPE-BSIs cases were collected. All-cause 30 day-mortality in children with CPE-BSIs (14.6%, 7/48) was significantly lower than that in adult patients (42.3%, 33/78, p = 0.001). The subgroup in adults empirically treated with tigecycline as an active drug displayed a significantly higher 30-days crude mortality (63.3%, 19/30) than the subgroup treated without tigecycline (29.2%, 14/48, p = 0.003). K. pneumoniae was the most prevalent species in both the pediatric (45.8%, 22/48) and adult populations (64.1%, 50/78), with discrepant carbapenemase genes in each population: 95.4% (21/22) of the pediatric K. pneumoniae isolates carried bla_NDM, while 82.0% (41/50) of the adult strains harbored bla_KPC. The ratio of E. coli in children (37.5%) was significantly higher than that in adults (12.8%, p = 0.002). In both populations, the majority of E. coli expressed bla_NDM, particularly bla_NDM−5. With statistical significance, bla_NDM was much more common in children (95.8%, 46/48) than in adults (34.6%, 27/78). The rate of multiple-heteroresistance phenotypes in children was as high as 87.5%, which was much lower in adults (57.1%). Agar dilution checkboard experiment against one pediatric carbapenemase-producing E. coli isolates showed that the combination of amikacin and fosfomycin yielded an additive effect. Overall, K. pneumoniae was the most common CPE-BSIs pathogen in both populations, with NDM-producing K. pneumoniae and KPC-producing ST11 K. pneumoniae being the most prevalent species in children and adults, respectively. E. coli was more prevalent in children than in adults, yet bla_NDM−5 was the most common carbapenem-resistant mechanism in E. coli in both populations. The wide range of multiple-heteroresistance combination traits found in different pathogen species from different host populations should provide a good foundation for future combination therapy design. Further investigations from more CPE isolates of various species are needed to evaluate the possible in vitro partial synergy of the amikacin and fosfomycin combination.