Therapeutic insights: Use of ceftazidime-avibactam in pediatric patients.

BACKGROUND: The increasing worldwide prevalence of multidrug-resistant (MDR) bacteria underscores the pressing demand for innovative therapeutic solutions. Ceftazidime-avibactam (CAZ-AVI) represents a promising new drug combination that has received approval for specific infection types. However, there is limited information regarding its application in pediatric patients. METHODS: This study investigates the effectiveness and adverse reactions associated with CAZ-AVI treatment in pediatric patients with life-threatening infections caused by MDR pathogens. The study was conducted at a tertiary children's hospital between December, 2021 and July, 2023. RESULTS: A total of 21 patients with life-threatening infections caused by MDR pathogens were enrolled in the study. All patients had underlying medical conditions: 10 had cerebral palsy, four had congenital neurometabolic disease, two had Nieman-Pick disease, two had cystic fibrosis, two had primary immunodeficiency, and one had leukemia. Among these, 12 patients had tracheostomies. Eight patients received CAZ- AVI monotherapy, and 13 patients received combination therapy. Microbiological eradication was achieved in 18 patients (85.7%), and a clinical response was observed in 20 patients (95.2%). Two patients (9.5%) experienced relapse with the same bacteria. One patient developed anaphylaxis, and one patient had elevated creatine phosphokinase levels that normalized following discontinuation of treatment. One patient died during the study period due to gastrointestinal bleeding. CONCLUSIONS: Ceftazidime-avibactam may be a promising new drug option for the treatment of life-threatening infections caused by MDR Gram-negative microorganisms in pediatric patients. However, further studies with larger case series are needed to further evaluate the efficacy and safety of CAZ-AVI in this population.

Ceftazidime-Avibactam as a Salvage Treatment for Severely Infected Immunosuppressed Children.

Background: Multidrug-resistant Gram-negative bacteria (MDR-GNB) are becoming increasingly common around the world, with carbapenems frequently serving as a last resort but being threatened by the growing incidence of carbapenemase-producing bacteria. Ceftazidime-avibactam (CAZ/AVI) is a potential agent against MDR-GNB but with limited clinical experience, particularly in critically ill immunosuppressed children. Methods: This study analyzed the use of CAZ/AVI as salvage treatment in severely infected immunosuppressed children from September 2019 to July 2022. Patients with confirmed GNB infection who received CAZ/AVI were matched with patients who received other antibiotics. Results: Twenty-five critically ill immunosuppressed children treated with CAZ/AVI were included. The majority had hematologic diseases. All patients presented with sepsis in all 30 courses. Septic shock presented in 36.7% of these courses. The primary sites of infection included bloodstream infection (20.0%), skin and skin structure infection (20.0%), intra-abdominal infection (13.3%) and hospital-acquired pneumonia (10.0%). Twelve of the 25 (48.0%) patients had positive microbiological cultures, mainly Pseudomonas aeruginosa and Klebsiella pneumoniae, including 5 carbapenem-resistant GNB-infected cases. Fifteen (50.0%) courses presented clinical improvement. For the initial course of each patient, the clinical response rate of the GNB recovered group was significantly higher than that of the group without GNB recovery (66.7% vs 23.1%, P = 0.047). The 14-day and 30-day mortality rates were 24.0% and 28.0%, respectively, which were significantly correlated with the absence of GNB recovery (P = 0.004 and 0.024, respectively) and hospital-acquired pneumonia as the primary site of infection (P = 0.001 and 0.006, respectively). There was no significant difference in major outcomes between patients who received CAZ/AVI and matched patients who received other antibiotics. Conclusion: CAZ/AVI could be considered a salvage strategy for immunosuppressed children with confirmed GNB infection. Caution should be taken when CAZ/AVI is applied to these patients in the absence of GNB recovery.

Pneumonia in an elderly Tibetan male caused by Shewanella algae: A case report.

RATIONALE: Shewanella algae are Gram-negative bacteria that are widely found in aquatic habitats and rarely cause lung infections in inland areas. PATIENT CONCERNS: Cough with light-yellow phlegm for 2 weeks. DIAGNOSES: The final diagnosis was bacterial pneumonia. INTERVENTIONS: The patient was treated with ceftazidime (2 g, every 12 h) for 1 week. OUTCOMES: The patient's lung infection improved and he was discharged. LESSONS: This case highlights a rare occurrence of lung infection caused by Shewanella algae in elderly Tibetan men residing in non-marine environments.

Septicaemia due to Vibrio vulnificus: A tropical infection not to be taken lightly.

Vibrio vulnificus is a halophilic gram-negative bacillus that can cause fulminant septicaemia in immunocompromised patients. A 67-year-old man who was immunosuppressed as a result of cytotoxic chemotherapy presented with a brief history of fever, lethargy, myalgia, and reduced oral intake. He had recently travelled to the beach to consume seafood. His blood pressure was 81/47 mm Hg, necessitating fluid resuscitation followed by inotropic support and admission to the intensive care unit. His blood culture was positive for curved gram-negative bacilli. The isolate was oxidase-positive and produced an acid butt with an alkaline slant in triple sugar iron agar. Matrix-assisted laser desorption ionization-time of flight mass spectrometry conclusively identified the isolate as V. vulnificus. Intravenous ceftazidime plus ciprofloxacin were administered, and by the fifth day of admission, he was successfully transferred out to the general ward. In total, the patient completed a 14-day course of antibiotic therapy.

Ceftazidime-avibactam resistance determination in carbapenem-resistant Klebsiella pneumoniae infections before its use in practice.

INTRODUCTION: To ensure the appropriate usage of ceftazidime-avibactam (CAZ-AVI), recently introduced in our hospital, we aimed to determine susceptibility rates, enzyme analysis, and clonal relationship among strains, together with clinical data. METHODOLOGY: Between June 1 and September 30, 2021, demographic and microbiological data of the patients were recorded. In the obtained samples, meropenem and colistin minimal inhibitory concentration (MIC) levels, carbapenem resistance genes, and the clonal relationship were studied by molecular methods. CAZ-AVI was not used in any of the patients. RESULTS: 140 carbapenem-resistant Klebsiella pneumoniae were isolated from 57 patients. Resistance to CAZ-AVI was found in 76 (54.3%) strains. Out of 57 patients, 31 (54.4%) isolates could be reached. Meropenem MIC level was ≥ 32 µg/mL in 26 (83.9%), and colistin MIC level was ≥ 4 µg/mL in 17 (54.8%) isolates. Enzyme analysis revealed NDM in 20 (64.5%), OXA-48 in 17 (54.8%), and KPC in seven (22.6%). NDM + OXA-48 was determined in 10 (32.2%) strains. NDM was determined in all CAZ-AVI resistant strains, OXA-48 in 16.1% (2/5) strains. Seven genotypes were detected. The largest cluster was genotype 3 clusters (11 isolates). Of 31 patients, 22 (71.0%) died. CAZ-AVI was susceptible in one of the patients who survived and four who died. CONCLUSIONS: Before using a new antibiotic, each center should determine the basal data and phenotypic/genotypic resistance ratios specific to that antibiotic. While a high NDM rate and low CAZ-AVI sensitivity limit the use of the drug in our center, it is clear that CAZ-AVI use in sensitive strains will decrease mortality.

Double blaKPC-2 copies quadrupled minimum inhibitory concentration of ceftazidime-avibactam in hospital-derived Klebsiella pneumoniae.

To illustrate the genomic and drug resistance traits of the Klebsiella pneumoniae Kpn_XM9, which harbors a transposon (Tn) As1 and was barely susceptible to ceftazidime-avibactam (CZA). Whole-genome sequencing, gene deletion, antimicrobial susceptibility, and conjugation tests were carried out to illustrate the traits of Kpn_XM9. As confirmed by whole-genome sequencing, the Kpn_XM9 harbored a 5,523,536 bp chromosome and five plasmids with lengths being 128,129, 196,512, 84,812, 43,695, and 5,596 bp, respectively. Plasmid p1_Kpn_XM9 (128,219 bp) contained four resistance genes, blaCTX-M-65, blaTEM-1B, rmtB, and two copies of blaKPC-2. Genes blaKPC-2 were bracketed by ISKpn17 and ISKpn16 within a new composite Tn3-like TnAs1. The two tandem repeats, positioned opposite each other, were spaced 93,447 bp apart in p1_Kpn_XM9. Kpn_XM9 belonged to K64 and sequence type (ST) 11. The Kpn_XM9 was resistant to amikacin, aztreonam, ticarcillin/clavulanic acid, piperacillin/tazobactam, ceftazidime, cefepime, imipenem, meropenem, tobramycin, ciprofloxacin, levofloxacin, doxycycline, minocycline, tigecycline, colistin, and trimethoprim/sulfamethoxazole; it was barely susceptible to CZA with a minimum inhibitory concentration of 8/4 µg/mL, which declined to 2/4 µg/mL after a 18,555 bp nucleotide was knocked out and one copy of blaKPC-2 was sustained on p1_Kpn_XM9. Kpn_XM9 had virulence genes encoding Types 1 and 3 fimbriae, four siderophores, and capsular polysaccharide anchoring protein but no genes upregulating capsular polysaccharide synthesis. The Kpn_XM9 presented a classical phenotype with extreme drug resistance. The emergence of double copies of blaKPC-2 in a single plasmid from the predominant ST11 K. pneumoniae represents a new therapeutic challenge.IMPORTANCEWith the wide use of ceftazidime-avibactam against carbapenem-resistant organisms, its resistance is increasingly documented; among the corresponding resistance mechanisms, mutations of blaKPC-2 or blaKPC-3 into other subtypes are dominant to date. However, more copies of blaKPC-2 may also greatly increase the minimum inhibitory concentration of ceftazidime-avibactam, which could be conferred by transposon As1 and insertion sequence 26 and should be of concern.

Crystal structure of the class A extended-spectrum ß-lactamase CTX-M-96 in complex with relebactam at 1.03 Angstrom resolution.

The use of ß-lactam/ß-lactamase inhibitors constitutes an important strategy to counteract ß-lactamases in multidrug-resistant (MDR) Gram-negative bacteria. Recent reports have described ceftazidime-/avibactam-resistant isolates producing CTX-M variants with different amino acid substitutions (e.g., P167S, L169Q, and S130G). Relebactam (REL) combined with imipenem has proved very effective against Enterobacterales producing ESBLs, serine-carbapenemases, and AmpCs. Herein, we evaluated the inhibitory efficacy of REL against CTX-M-96, a CTX-M-15-type variant. The CTX-M-96 structure was obtained in complex with REL at 1.03 Å resolution (PDB 8EHH). REL was covalently bound to the S70-Oγ atom upon cleavage of the C7-N6 bond. Compared with apo CTX-M-96, binding of REL forces a slight displacement of the deacylating water inwards the active site (0.81 Å), making the E166 and N170 side chains shift to create a proper hydrogen bonding network. Binding of REL also disturbs the hydrophobic patch formed by Y105, P107, and Y129, likely due to the piperidine ring of REL that creates clashes with these residues. Also, a remarkable change in the positioning of the N104 sidechain is also affected by the piperidine ring. Therefore, differences in the kinetic behavior of REL against class A ß-lactamases seem to rely, at least in part, on differences in the residues being involved in the association and stabilization of the inhibitor before hydrolysis. Our data provide the biochemical and structural basis for REL effectiveness against CTX-M-producing Gram-negative pathogens and essential details for further DBO design. Imipenem/REL remains an important choice for dealing with isolates co-producing CTX-M with other ß-lactamases.

Synergistic antibacterial activity of ceftazidime-avibactam in combination with colistin, gentamicin, amikacin, and fosfomycin against carbapenem-resistant Klebsiella pneumoniae.

Carbapenem-resistant Klebsiella pneumoniae (CPKP) infections seriously threaten global public health. The main objective of this study was to assess the in-vitro synergistic activity of ceftazidime-avibactam (CZA) in combination with colistin (COL), amikacin (AK), gentamicin (GEN), and fosfomycin (FOS) against CPKP isolates. The secondary goal was to determine the antibiotic susceptibility performance of BD Phoenix. OXA-48 (49.1%) was the predominant carbapenemase, followed by KPC (29.1%). We used the broth microdilution (BMD) method to determine the minimum inhibitory concentrations (MICs) of CZA, COL, AK, and GEN. Meanwhile, the MICs of FOS were determined by the agar dilution (AD) method. To examine the antibacterial activity of CZA, we conducted a checkerboard assay (CBA) with COL, AK, GEN, and FOS against CRKP isolates. We randomly selected three strains and performed synergy testing via time-kill assay (TKA). CRKP isolates were 89.1% susceptible to CZA, 16.4% to COL, 21.8% to GEN, and 29.1% to AK using BMD, 47.3% to FOS by AD. The most synergistic effects were observed in the combination of CZA-COL (78.2%) and CZA-FOS (63.6%). Given the limited therapeutic options for treating severe CRKP infections, combining CZA with COL and FOS may enhance in-vitro activity against clinical CRKP isolates.

Silver nanoparticle with potential antimicrobial and antibiofilm efficiency against multiple drug resistant, extensive drug resistant Pseudomonas aeruginosa clinical isolates.

BACKGROUND: The study aims to investigate the effect of combining silver nanoparticles (AGNPs) with different antibiotics on multi-drug resistant (MDR) and extensively drug resistant (XDR) isolates of Pseudomonas aeruginosa (P. aeruginosa) and to investigate the mechanism of action of AGNPs. METHODS: AGNPs were prepared by reduction of silver nitrate using trisodium citrate and were characterized by transmission electron microscope (TEM) in addition to an assessment of cytotoxicity. Clinical isolates of P. aeruginosa were collected, and antimicrobial susceptibility was conducted. Multiple Antibiotic Resistance (MAR) index was calculated, and bacteria were categorized as MDR or XDR. Minimum inhibitory concentration (MIC) of gentamicin, ciprofloxacin, ceftazidime, and AGNPs were determined. The mechanism of action of AGNPs was researched by evaluating their effect on biofilm formation, swarming motility, protease, gelatinase, and pyocyanin production. Real-time PCR was performed to investigate the effect on the expression of genes encoding various virulence factors. RESULTS: TEM revealed the spherical shape of AGNPs with an average particle size of 10.84 ± 4.64 nm. AGNPS were safe, as indicated by IC50 (42.5 µg /ml). The greatest incidence of resistance was shown against ciprofloxacin which accounted for 43% of the bacterial isolates. Heterogonous resistance patterns were shown in 63 isolates out of the tested 107. The MAR indices ranged from 0.077 to 0.84. Out of 63 P. aeruginosa isolates, 12 and 13 were MDR and XDR, respectively. The MIC values of AGNPs ranged from 2.65 to 21.25 µg /ml. Combination of AGNPs with antibiotics reduced their MIC by 5-9, 2-9, and 3-10Fold in the case of gentamicin, ceftazidime, and ciprofloxacin, respectively, with synergism being evident. AGNPs produced significant inhibition of biofilm formation and decreased swarming motility, protease, gelatinase and pyocyanin production. PCR confirmed the finding, as shown by decreased expression of genes encoding various virulence factors. CONCLUSION: AGNPs augment gentamicin, ceftazidime, and ciprofloxacin against MDR and XDR Pseudomonas isolates. The efficacy of AGNPs can be attributed to their effect on the virulence factors of P. aeruginosa. The combination of AGNPs with antibiotics is a promising strategy to attack resistant isolates of P. aeruginosa.

Long-term antibiotic exposure landscapes and resistant Escherichia coli colonization in a densely populated setting.

Antibiotic exposure is associated with resistant bacterial colonization, but this relationship can be obscured in community settings owing to horizontal bacterial transmission and broad distributions. Locality-level exposure estimates considering inhabitants' length of stay, exposure history, and exposure conditions of areas nearby could clarify these relationships. We used prescription data filled during 2010-2015 for 23 antibiotic types for members of georeferenced households in a population-based infectious disease surveillance platform. For each antibiotic and locality, we generated exposure estimates, expressed in defined daily doses (DDD) per 1000 inhabitant days of observation (IDO). We also estimated relevant environmental parameters, such as the distance of each locality to water, sanitation, and other amenities. We used data on ampicillin, ceftazidime, and trimethoprim-and-sulfamethoxazole resistant Escherichia coli colonization from stool cultures of asymptomatic individuals in randomly selected households. We tested exposure-colonization associations using permutation analysis of variance and logistic generalized linear mixed-effect models. Overall, exposure was highest for trimethoprim-sulfamethoxazole (1.8 DDD per 1000 IDO), followed by amoxicillin (0.7 DDD per 1000 IDO). Of 1,386 unique household samples from 195 locations tested between September 2015 and January 2016, 90%, 85% and 4% were colonized with E. coli resistant to trimethoprim and sulfamethoxazole, ampicillin, and ceftazidime, respectively. Ceftazidime-resistant E. coli colonization was common in areas with increased trimethoprim-sulfamethoxazole, cloxacillin, and erythromycin exposure. No association with any of the physical environmental variables was observed. We did not detect relationships between distribution patterns of ampicillin or trimethoprim-and-sulfamethoxazole resistant E. coli colonization and the risk factors assessed. Appropriate temporal and spatial scaling of raw antibiotic exposure data to account for evolution and ecological contexts of antibiotic resistance could clarify exposure-colonization relationships in community settings and inform community stewardship program.

Analysis of the Antimicrobial Activity of Epigallocatechin-3-Gallate (EGCG).

We studied antimicrobial activity of epigallocatechin-3-gallate (EGCG), a green tea polyphenolic catechin, and its combined use with ceftazidime (CAZ) against bacterial strains of Klebsiella pneumoniae. EGCG exhibited no activity against strains of K. pneumoniae with a different sensitivity to CAZ. However, for a "sensitive" strain, a decrease in minimum inhibitory concentration (MIC) of CAZ (from 0.064 to 0.023 mg/liter) was revealed when CAZ was co-administered with EGCG. For a "resistant" stain, MIC of CAZ remained high, but activation of EGCG at its high concentrations was observed. Indirect evidence of antimicrobial effect of EGCG co-administered with CAZ on Klebsiella was obtained.

A large-scale surveillance revealed that KPC variants mediated ceftazidime-avibactam resistance in clinically isolated Klebsiella pneumoniae.

To monitor the resistance rate and gain a deeper understanding of the resistance mechanisms, we conducted over a 2-year surveillance focusing on the Klebsiella pneumoniae associated with the clinical usage of ceftazidime-avibactam (CZA) in a teaching hospital. A total of 4,641 K. pneumoniae isolates were screened to identify the CZA resistance through antimicrobial susceptibility testing. Comprehensive analyses, including homology analysis, conjugation experiments, clone assays, and whole genome sequencing, were furtherly performed on the CZA-resistant strains. In total, four CZA-resistant K. pneumoniae (CZA-R-Kp) strains were separated from four patients, in which three of them received CZA treatment during the hospitalization, accounting for a 4% (3/75) resistance development rate of K. pneumoniae under CZA stress. All CZA-R-Kp isolates were found to possess variants of blaKPC-2. The identified mutations included blaKPC-33, blaKPC-86, and a novel variant designated as blaKPC-129, all of which were located in the Ω loop of the KPC enzyme. These mutations were found to impact the amino acid sequence and spatial structure of the enzyme's active center, consequently affecting KPC carbapenemase activity. This study underscores the importance of active surveillance to monitor the emergence of resistance to CZA, highlighting the need for ongoing research to develop effective strategies for combating antimicrobial resistance. Understanding the mechanisms behind resistance is crucial in maintaining the efficacy of CZA, a vital tool in the battle against multidrug-resistant infections.IMPORTANCEAs an effective drug for the treatment of carbapenem-resistant Klebsiella pneumoniae, ceftazidime-avibactam (CZA) began to develop resistance in recent years and showed an increasing trend. In order to effectively monitor the resistance rate of CZA and understand its resistance mechanism, we monitored K. pneumoniae for more than 2 years to find CZA-resistant strains. Through comprehensive analysis of the selected CZA-resistant strains, it was found that all the CZA-resistant strains had mutation, which could affect the activity of KPC carbapenemase. This study highlights the importance of proactive surveillance to monitor the emergence of CZA resistance, which highlights the need for ongoing research to develop effective strategies to combat antimicrobial resistance. Understanding the mechanisms behind resistance is critical to maintaining the effectiveness of CZA, an important tool in the fight against multidrug-resistant infections.

Point mutation P174L of the penA gene endowing ceftazidime resistance to Burkholderia pseudomallei in China.

In a clinical isolate of Burkholderia pseudomallei from Hainan, the association between the emergence of ceftazidime resistance and a novel PenA P174L allele was identified for the first time, providing an understanding of one mechanism by which ceftazidime resistance arises in B. pseudomallei.

Molecular characterization of carbapenem and ceftazidime-avibactam-resistant Enterobacterales and horizontal spread of bla NDM-5 gene at a Lebanese medical center.

Introduction: In the battle against multidrug-resistant bacterial infections, ceftazidime- avibactam (CZA) stands as a pivotal defense, particularly against carbapenemresistant (CR) Gram-negative pathogens. However, the rise in resistance against this drug poses a significant threat to its effectiveness, highlighting the critical need for in-depth studies about its resistance mechanisms. Methods: This research focuses on the genomic characterization of CR- and CZA-resistant Escherichia coli (n=26) and Klebsiella pneumoniae (n=34) strains, harboring the blaNDM and/or blaOXA-48-like genes, at a major Lebanese tertiary care medical center, using whole genome sequencing (WGS). Results: Our findings revealed a notable prevalence of blaNDM in all K. pneumoniae strains isolates, with 27 of these also harboring blaOXA-48. On the other hand, E. coli strains predominantly carried the blaNDM-5 gene. Whole genome sequencing (WGS) identified a predominance of ST383 among K. pneumoniae strains, which possessed a multi-replicon IncFIB-IncHI1B plasmid harboring the blaNDM-5. Additionally, various Inc group plasmids in K. pneumoniae across multiple sequence types were found to carry the blaNDM. Similarly, diverse STs of E. coli were observed to carry blaNDM-5 on different plasmids. Discussion: The study underscores NDM carbapenemases as a paramount resistance mechanism in Lebanon,jeopardizing critical last-resort treatments. It also illuminates the role of varied sequence types and mobile genetic elements in the spread of NDM resistance,stressing the urgent need for strategies to mitigate this threat, especially in nosocomial infections.

Evolution of blaKPC Under the Pressure of Carbapenems and Ceftazidime/Avibactam in a Patient With Persistent Bacteremia Caused by Klebsiella pneumoniae.

A 30-year-old Korean man with myelodysplastic syndrome admitted hospital due to undifferentiated fever and recurrent skin lesions. He received combination therapy with high doses of meropenem, tigecycline and amikacin, yielding carbapenem resistant Klebsiella pneumoniae (CRKP) harboring K. pneumoniae carbapenemase (KPC)-2 from blood cultures on hospital day (HD) 23. Ceftazidime/avibactam was started at HD 37 and CRKP was eradicated from blood cultures after 5 days. However, ceftazidime/avibactam-resistant CRKP carrying KPC-44 emerged after 26 days of ceftazidime/avibactam treatment and then ceftazidime/avibactam-resistant, carbapenem-susceptible K. pneumoniae carrying KPC-135 was isolated on HD 65. The 3-D homology of KPC protein showed that hot spot changes in the omega loop could be attributed to ceftazidime/avibactam resistance and loss of carbapenem resistance. Whole genome sequencing of serial isolates supported that phenotypic variation was due to clonal evolution than clonal replacement. The treatment regimen was changed from CAZ/AVI to meropenem-based therapy (meropenem 1 g iv q 8 hours and amikacin 600 mg iv per day) starting with HD 72. CAZ/AVI-susceptible CRKP was presented again from blood cultures on HD 84, and the patient expired on HD 85. This is the first Korean report on the acquisition of ceftazidime/avibactam resistance through the emergence of blaKPC variants.

Clinical outcomes in patients infected with ertapenem-only-resistant Enterobacterales versus multi-carbapenem-resistant Enterobacterales.

BACKGROUND: Use of anti-carbapenem-resistant Enterobacterales (anti-CRE) agents such as ceftazidime/avibactam has been associated with improved clinical outcome in cohorts that primarily include patients infected with CRE that are resistant to meropenem (MCRE). OBJECTIVES: To clarify whether patients with CRE resistant to ertapenem but susceptible to meropenem (ertapenem-only-resistant Enterobacterales; EORE) benefit from therapy with anti-CRE agents. METHODS: Patients treated for CRE infection in hospitals in the USA between 2016 and 2019 and enrolled in the CRACKLE-2 study were included. The primary outcome was the desirability of outcome ranking (DOOR) assessed at 30 days after index cultures. RESULTS: The EORE group included 213 patients and the MCRE group included 643. The demographics were similar between the groups except for the patients' race and origin before admission. The MCRE group received anti-CRE agents for definitive therapy significantly more frequently compared with the EORE group (30% versus 5% for ceftazidime/avibactam). We did not observe a significant difference between the groups in the adjusted DOOR probability of a more desirable outcome for a randomly selected patient in the EORE group compared with the MCRE group (52.5%; 95% CI, 48.3%-56.7%). The MCRE group had a similar proportion of patients who died at 30 days (26% versus 21%) and who were discharged to home (29% versus 40%), compared with the EORE group. CONCLUSIONS: Patients with clinical EORE infection rarely received anti-CRE agents, but attained similar outcomes compared with patients with MCRE infection. The findings support current IDSA treatment guidance for meropenem- or imipenem-based therapy for treatment of EORE infections.

The prevalence and mechanisms of heteroresistance to ceftazidime/avibactam in KPC-producing Klebsiella pneumoniae.

OBJECTIVES: To investigate the prevalence and mechanisms of ceftazidime/avibactam heteroresistance in KPC-producing Klebsiella pneumoniae (KPC-KP) isolates, as well as the role of heteroresistance in the transition of ceftazidime/avibactam susceptibility to resistance. METHODS: Clinical KPC-KP isolates were obtained from a tertiary hospital in China from 2016 to 2017 and 2019 to 2020. Antimicrobial susceptibility was determined by the broth microdilution method. Population analysis profiles were used to assess ceftazidime/avibactam heteroresistance. WGS and molecular cloning were conducted to reveal heteroresistance mechanisms and molecular characteristics. RESULTS: The findings indicated that the transition of ceftazidime/avibactam susceptibility to resistance during the treatment of KPC-KP infection is primarily attributed to the heteroresistance exhibited by KPC-KP isolates towards ceftazidime/avibactam. Among 355 ceftazidime/avibactam-susceptible KPC-KP isolates (indicating a resistance rate of 0%), 41 (11.55%) exhibited ceftazidime/avibactam heteroresistance, with the primary mechanism being the presence of KPC mutant subpopulations. These KPC variants, arising from point mutations, deletions and insertions, significantly increased ceftazidime/avibactam resistance while alongside enhanced carbapenem susceptibility. Notably, 11 new KPC variants were identified. Furthermore, four heteroresistant isolates were caused by mixed infection involving subpopulations carrying NDM-1 or NDM-5. Phylogenetic analysis indicated that the clonal spread of ST11-KL64 KPC-KP may be correlated with the prevalence of heteroresistance. CONCLUSIONS: Ceftazidime/avibactam heteroresistance, primarily driven by pre-existing KPC variants, underscores the importance of considering heteroresistance in ceftazidime/avibactam therapeutics. Awareness of these dynamics is crucial for the effective and sustainable clinical application of ceftazidime/avibactam.

Resistance to ceftazidime-avibactam and other new ß-lactams in Pseudomonas aeruginosa clinical isolates: a multi-center surveillance study.

New ß-lactam-ß-lactamase inhibitor combinations represent last-resort antibiotics to treat infections caused by multidrug-resistant Pseudomonas aeruginosa. Carbapenemase gene acquisition can limit their spectrum of activity, and reports of resistance toward these new molecules are increasing. In this multi-center study, we evaluated the prevalence of resistance to ceftazidime-avibactam (CZA) and comparators among P. aeruginosa clinical isolates from bloodstream infections, hospital-acquired or ventilator-associated pneumonia, and urinary tract infections, circulating in Southern Italy. We also investigated the clonality and content of relevant ß-lactam resistance mechanisms of CZA-resistant (CZAR) isolates. A total of 120 P. aeruginosa isolates were collected. CZA was among the most active ß-lactams, retaining susceptibility in the 81.7% of cases, preceded by cefiderocol (95.8%) and followed by ceftolozane-tazobactam (79.2%), meropenem-vaborbactam (76.1%), imipenem-relebactam (75%), and aztreonam (69.6%). Among non-ß-lactams, colistin and amikacin were active against 100% and 85.8% of isolates respectively. In CZAR strains subjected to whole-genome sequencing (n = 18), resistance was mainly due to the expression of metallo-ß-lactamases (66.6% VIM-type and 5.5% FIM-1), followed by PER-1 (16.6%) and GES-1 (5.5%) extended-spectrum ß-lactamases, mostly carried by international high-risk clones (ST111 and ST235). Of note, two strains producing the PER-1 enzyme were resistant to all ß-lactams, including cefiderocol. In conclusion, the CZA resistance rate among P. aeruginosa clinical isolates in Southern Italy remained low. CZAR isolates were mostly metallo-ß-lactamases producers and belonging to ST111 and ST253 epidemic clones. It is important to implement robust surveillance systems to monitor emergence of new resistance mechanisms and to limit the spread of P. aeruginosa high-risk clones. IMPORTANCE: Multidrug-resistant Pseudomonas aeruginosa infections are a growing threat due to the limited therapeutic options available. Ceftazidime-avibactam (CZA) is among the last-resort antibiotics for the treatment of difficult-to-treat P. aeruginosa infections, although resistance due to the acquisition of transferable ß-lactamase genes is increasing. With this work, we report that CZA represents a highly active antipseudomonal ß-lactam compound (after cefiderocol), and that metallo-ß-lactamases (VIM-type) and extended-spectrum ß-lactamases (GES and PER-type) production is the major factor underlying CZA resistance in isolates from Southern Italian hospitals. In addition, we reported that such resistance mechanisms were mainly carried by the international high-risk clones ST111 and ST235.

Dynamic evolution of ceftazidime-avibactam resistance from a single patient through the IncX3_NDM-5 plasmid transfer and blaKPC 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 ß-lactam/ß-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.

Tracking emergence and outbreak of Klebsiella pneumoniae co-producing NDM-1 and KPC-2 after sulfamethoxazole-trimethoprim treatment: Insights from genetic analysis.

The co-production of KPC and NDM carbapenemases in carbapenem-resistant Klebsiella pneumoniae (CRKP) complicates clinical treatment and increases mortality rates. The emergence of KPC-NDM CRKP is believed to result from the acquisition of an NDM plasmid by KPC CRKP, especially under the selective pressure of ceftazidime-avibactam (CZA). In this study, a CRKP-producing KPC-2 (JNP990) was isolated from a patient at a tertiary hospital in Shandong Province, China. Following sulfamethoxazole-trimethoprim (SXT) treatment, the isolate evolved into a strain that co-produces KPC and NDM (JNP989), accompanied by resistance to SXT (minimum inhibitory concentration >2/38 µg/mL) and CZA (dd ≤14 mm). Whole-genome sequencing and S1 nuclease pulsed-field gel electrophoresis revealed that JNP989 acquired an IncC plasmid (NDM plasmid) spanning 197 kb carrying sul1 and blaNDM-1 genes. The NDM plasmid could be transferred successfully into Escherichia coli J53 at a conjugation frequency of (8.70±2.47) × 10-4. The IncFⅡ/IncR plasmid carrying the blaKPC-2 gene in JNP990 could only be transferred in the presence of the NDM plasmid at a conjugation frequency of (1.93±0.41) × 10-5. Five CRKP strains with the same resistance pattern as JNP989, belonging to the same clone as JNP989, with sequence type 11 were isolated from other patients in the same hospital. Two strains lost resistance to CZA due to the loss of the blaNDM-1-carrying fragment mediated by insertion sequence 26. Plasmid stability testing indicated that the IncC plasmid was more stable than the blaNDM-1 genes in the hosts. This study describes the evolution of KPC-NDM CRKP and its spread in hospitalized patients following antibiotic treatment, highlighting the severity of the spread of resistance.