Systematic Review and Meta-Analysis of Clinical Efficacy and Safety of Meropenem-Vaborbactam versus Best-Available Therapy in Patients with Carbapenem-Resistant Enterobacteriaceae Infections.

Antimicrobial resistance is increasingly concerning, causing millions of deaths and a high cost burden. Given that carbapenemase-producing Enterobacterales are particularly concerning due to their ability to develop structural modifications and produce antibiotic-degrading enzymes, leading to high resistance levels, we sought to summarize the available data on the efficacy and safety regarding the combination of meropenem-vaborbactam (MV) versus the best available therapy (BAT). Articles related to our objective were searched in the PubMed and Scopus databases inception to July 2024. To assess the quality of the studies, we used the Cochrane risk-of-bias tool, RoB2. The outcomes were pooled as a risk ratio (RR) and a 95% confidence interval (95%CI). A total of four published studies were involved: one retrospective cohort study and three phase 3 trials, including 432 patients treated with MV and 426 patients treated with BAT (mono/combination therapy with polymyxins, carbapenems, aminoglycosides, colistin, and tigecycline; or ceftazidime-avibactam; or piperacillin-tazobactam). No significant difference in the clinical response rate was observed between MV and the comparators at the TOC (RR = 1.29, 95%CI [0.92, 1.80], p = 0.14) and EOT (RR = 1.66, 95%CI [0.58, 4.76], p = 0.34) visits. MV was associated with a similar microbiological response as the comparators at TOC (RR = 1.63, 95%CI [0.85, 3.11], p = 0.14) and EOT assessment (RR = 1.16, 95%CI [0.88, 1.54], p = 0.14). In the pooled analysis of the four studies, 28-day all-cause mortality was lower for MV than the control groups (RR = 0.47, 95%CI [0.24, 0.92], p = 0.03). MV was associated with a similar risk of adverse events (AEs) as comparators (RR = 0.79, 95%CI [0.53, 1.17], p = 0.23). Additionally, MV was associated with fewer renal-related AEs than the comparators (RR = 0.32, 95%CI [0.15, 0.66], p = 0.002). MV was associated with a similar risk of treatment discontinuation due to AEs (RR = 0.76, 95%CI [0.38, 1.49], p = 0.42) or drug-related AEs (RR = 0.56, 95%CI [0.28, 1.10], p = 0.09) as the comparators. In conclusion, MV presents a promising therapeutic option for treating CRE infections, demonstrating similar clinical and microbiological responses as other comparators, with potential advantages in mortality outcomes and renal-related AEs.

The effect of combinations of a glyphosate-based herbicide with various clinically used antibiotics on phenotypic traits of Gram-negative species from the ESKAPEE group.

The emission of glyphosate and antibiotic residues from human activities threatens the diversity and functioning of the microbial community. This study examines the impact of a glyphosate-based herbicide (GBH) and common antibiotics on Gram-negative bacteria within the ESKAPEE group (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter spp. and Escherichia coli). Ten strains, including type and multidrug-resistant strains for each species were analysed and eight antibiotics (cefotaxime, meropenem, aztreonam, ciprofloxacin, gentamicin, tigecycline, sulfamethoxazole-trimethoprim, and colistin) were combined with the GBH. While most combinations yielded additive or indifferent effects in 70 associations, antagonistic effects were observed with ciprofloxacin and gentamicin in five strains. GBH notably decreased the minimum inhibitory concentration of colistin in eight strains and displayed synergistic activity with meropenem against metallo-ß-lactamase (MBL)-producing strains. Investigation into the effect of GBH properties on outer membrane permeability involved exposing strains to a combination of this GBH and vancomycin. Results indicated that GBH rendered strains sensitive to vancomycin, which is typically ineffective against Gram-negative bacteria. Furthermore, we examined the impact of GBH in combination with three carbapenem agents on 14 strains exhibiting varying carbapenem-resistance mechanisms to assess its effect on carbapenemase activity. The GBH efficiently inhibited MBL activity, demonstrating similar effects to EDTA (ethylenediaminetetraacetic acid). Chelating effect of GBH may have multifaceted impacts on bacterial cells, potentially by increasing outer membrane permeability and inactivating metalloenzyme activity.

Efficacy of aspergillomarasmine A/meropenem combinations with and without avibactam against bacterial strains producing multiple ß-lactamases.

The effectiveness of ß-lactam antibiotics is increasingly threatened by resistant bacteria that harbor hydrolytic ß-lactamase enzymes. Depending on the class of ß-lactamase present, ß-lactam hydrolysis can occur through one of two general molecular mechanisms. Metallo-ß-lactamases (MBLs) require active site Zn2+ ions, whereas serine-ß-lactamases (SBLs) deploy a catalytic serine residue. The result in both cases is drug inactivation via the opening of the ß-lactam warhead of the antibiotic. MBLs confer resistance to most ß-lactams and are non-susceptible to SBL inhibitors, including recently approved diazabicyclooctanes, such as avibactam; consequently, these enzymes represent a growing threat to public health. Aspergillomarasmine A (AMA), a fungal natural product, can rescue the activity of the ß-lactam antibiotic meropenem against MBL-expressing bacterial strains. However, the effectiveness of this ß-lactam/ß-lactamase inhibitor combination against bacteria producing multiple ß-lactamases remains unknown. We systematically investigated the efficacy of AMA/meropenem combination therapy with and without avibactam against 10 Escherichia coli and 10 Klebsiella pneumoniae laboratory strains tandemly expressing single MBL and SBL enzymes. Cell-based assays demonstrated that laboratory strains producing NDM-1 and KPC-2 carbapenemases were resistant to the AMA/meropenem combination but became drug-susceptible upon adding avibactam. We also probed these combinations against 30 clinical isolates expressing multiple ß-lactamases. E. coli, Enterobacter cloacae, and K. pneumoniae clinical isolates were more susceptible to AMA, avibactam, and meropenem than Pseudomonas aeruginosa and Acinetobacter baumannii isolates. Overall, the results demonstrate that a triple combination of AMA/avibactam/meropenem has potential for empirical treatment of infections caused by multiple ß-lactamase-producing bacteria, especially Enterobacterales.

Molecular characterization of NDM and OXA-48-like-producing Klebsiella pneumoniae ST16 and hypervirulent ST337 clone among two patients; a case report.

Carbapenem-resistant Klebsiella pneumoniae (CRKP) infections are a major public health problem, requiring the use of last-resort antibiotics such as colistin. However, there is concern regarding the emergence of isolates resistant to this agent. The report describes two patients with urinary tract infection (UTI) and ventilator-associated pneumonia (VAP) infection caused by CRKP strains. The first case was a 23-year-old male with UTI caused by a strain of ST16 co-harboring blaCTX-M, blaTEM, blaSHV, blaNDM, blaOXA-48-like genes. The second case was a 39-year-old woman with VAP due to hypervirulent ST337-K2 co-harboring blaSHV, blaNDM, blaOXA-48-like, iucA, rmpA2 and rmpA. The patients' general condition improved after combination therapy with colistin (plus meropenem and rifampin, respectively) and both of them recovered and were discharged from the hospital. This study highlights the necessary prevention and control steps to prevent the further spread of CRKP strains should be a priority in our hospital.

A new type of Class C ß-lactamases defined by PIB-1. A metal-dependent carbapenem-hydrolyzing ß-lactamase, from Pseudomonas aeruginosa: Structural and functional analysis.

Antibiotic resistance is one of most important health concerns nowadays, and ß-lactamases are the most important resistance determinants. These enzymes, based on their structural and functional characteristics, are grouped in four categories (A, B, C and D). We have solved the structure of PIB-1, a Pseudomonas aeruginosa chromosomally-encoded ß-lactamase, in its apo form and in complex with meropenem and zinc. These crystal structures show that it belongs to the Class C ß-lactamase group, although it shows notable differences, especially in the Ω- and P2-loops, which are important for the enzymatic activity. Functional analysis showed that PIB-1 is able to degrade carbapenems but not cephalosporins, the typical substrate of Class C ß-lactamases, and that its catalytic activity increases in the presence of metal ions, especially zinc. They do not bind to the active-site but they induce the formation of trimers that show an increased capacity for the degradation of the antibiotics, suggesting that this oligomer is more active than the other oligomeric species. While PIB-1 is structurally a Class C ß-lactamase, the low sequence conservation, substrate profile and its metal-dependence, prompts us to position this enzyme as the founder of a new group inside the Class C ß-lactamases. Consequently, its diversity might be wider than expected.

The effects of single and multiple resistance mechanisms on bacterial response to meropenem.

OBJECTIVES: Meropenem is commonly used against Pseudomonas aeruginosa. Traditionally, the time unbound antibiotic concentration exceeds the MIC (fT>MIC) is used to select carbapenem regimens. We aimed to characterize the effects of different baseline resistance mechanisms on bacterial killing and resistance emergence; evaluate whether fT>MIC can predict these effects; and, develop a novel Quantitative and Systems Pharmacology (QSP) model to describe the effects of baseline resistance mechanisms on the time-course of bacterial response. METHODS: Seven isogenic P. aeruginosa strains with a range of resistance mechanisms and MICs were used in 10-day hollow-fiber infection model studies. Meropenem pharmacokinetic profiles were simulated for various regimens (t1/2,meropenem = 1.5 h). All viable counts on drug-free, 3 × MIC, and 5 × MIC meropenem-containing agar across all strains, five regimens, and control (n = 90 profiles) were simultaneously subjected to QSP modeling. Whole genome sequencing was completed for total population samples and emergent resistant colonies at 239 h. RESULTS: Regimens achieving ≥98%fT>1×MIC suppressed resistance emergence of the mexR knockout strain. Even 100%fT>5 × MIC failed to achieve this against the strain with OprD loss and the ampD and mexR double-knockout strain. Baseline resistance mechanisms affected bacterial outcomes, even for strains with the same MIC. Genomic analysis revealed that pre-existing resistant subpopulations drove resistance emergence. During meropenem exposure, mutations in mexR were selected in strains with baseline oprD mutations, and vice versa, confirming these as major mechanisms of resistance emergence. Secondary mutations occurred in lysS or argS, coding for lysyl and arginyl tRNA synthetases, respectively. DISCUSSION: The QSP model well-characterized all bacterial outcomes of the seven strains simultaneously, which fT>MIC could not.

Predicting early appropriate therapy for patients infected by carbapenem-resistant Gram-negative pathogens in intensive care units in Italy.

BACKGROUND: Antibiotic resistance among Gram-negative bacteria in intensive care units (ICUs) is linked with high morbidity and mortality in patients. In this study, we estimated the therapeutic coverage of various antibiotics, focusing on cefiderocol and comparators, administered empirically against an infection of unknown origin in the ICU. METHODS: In the ARTEMIS surveillance study, susceptibilities of 624 Italian Gram-negative isolates to amikacin, aztreonam-avibactam, cefiderocol, ceftazidime-avibactam, ceftolozane-tazobactam, colistin, imipenem-relebactam, meropenem, and meropenem-vaborbactam were tested by broth microdilution, and results were interpreted by European Committee on Antimicrobial Susceptibility Testing breakpoints. The susceptibility rates from the ARTEMIS study were extrapolated to Gram-negative isolates obtained from 5,774 patients in Italian ICUs in 2021. The sum of the predicted susceptibilities of individual pathogens represented the overall likelihood of in vitro activity of each antibiotic as early targeted therapy for ICU patients. RESULTS: A total of 624 Italian Gram-negative isolates included 206 Pseudomonas aeruginosa, 138 Acinetobacter baumannii, 187 Klebsiella pneumoniae, and 93 Escherichia coli. Against A. baumannii, K. pneumoniae, P. aeruginosa, and E. coli, the overall susceptibility rates for cefiderocol were 87.7%, 96.8%, 99%, and 100%, respectively; and for comparator agents, 8.7-96.4%, 25.7-100%, 73.3-100%, and 89.2-100%, respectively. Among the subset of meropenem-resistant isolates, susceptibility rates of A. baumannii, K. pneumoniae, and P. aeruginosa to cefiderocol were 86.4%, 96.2% and 100%, respectively. Corresponding susceptibility rates to comparator agents were 0-96.8%, 0-100%, and 6.4-100%, respectively. There were no meropenem-resistant isolates of E. coli. The extrapolation of data to isolates from Italian ICUs showed that the highest likelihood of therapeutic coverage, both overall and among meropenem-resistant isolates, was reported for colistin (96.8% and 72.2%, respectively) and cefiderocol (95.7% and 71.4%, respectively). All other antibiotics were associated with a likelihood below 73% overall and between 0% and 41.4% for meropenem-resistant isolates. CONCLUSIONS: Based on confirmed susceptibility rates and reported ICU prevalence of multiple Gram-negative species, cefiderocol showed a higher predicted therapeutic coverage and utility in ICUs compared with comparator beta-lactam-beta-lactamase inhibitor antibiotics. Cefiderocol may be a promising early treatment option for patients at high risk of carbapenem-resistant Gram-negative bacterial infections in the ICU.

A Systematic Review of the Pharmacokinetics and Pharmacodynamics of Novel Beta-Lactams and Beta-Lactam with Beta-Lactamase Inhibitor Combinations for the Treatment of Pneumonia Caused by Carbapenem-Resistant Gram-Negative Bacteria.

BACKGROUND: Novel beta-lactams show activity against many multidrug-resistant Gram-negative bacteria that cause severe lung infections. Understanding pharmacokinetic/pharmacodynamic characteristics of these agents may help optimise outcomes in the treatment of pneumonia. OBJECTIVES: To describe and appraise studies that report pulmonary pharmacokinetic and pharmacodynamic data of cefiderocol, ceftazidime/avibactam, ceftolozane/tazobactam, imipenem/cilastatin/relebactam and meropenem/vaborbactam. METHODS: MEDLINE (PubMed), Embase, Web of Science and Scopus libraries were used for the literature search. Pulmonary population pharmacokinetic and pharmacokinetic/pharmacodynamic studies on adult patients receiving cefiderocol, ceftazidime/avibactam, ceftolozane/tazobactam, imipenem/cilastatin/relebactam, and meropenem/vaborbactam published in peer-reviewed journals were included. Two independent authors screened, reviewed and extracted data from included articles. A reporting guideline for clinical pharmacokinetic studies (ClinPK statement) was used for bias assessment. Relevant outcomes were included, such as population pharmacokinetic parameters and probability of target attainment of dosing regimens. RESULTS: Twenty-four articles were included. There was heterogeneity in study methods and reporting of results, with diversity across studies in adhering to the ClinPK statement checklist. Ceftolozane/tazobactam was the most studied agent. Only two studies collected epithelial lining fluid samples from patients with pneumonia. All the other phase I studies enrolled healthy subjects. Significant population heterogeneity was evident among available population pharmacokinetic models. Probabilities of target attainment rates above 90% using current licensed dosing regiments were reported in most studies. CONCLUSIONS: Although lung pharmacokinetics was rarely described, this review observed high target attainment using plasma pharmacokinetic data for all novel beta-lactams. Future studies should describe lung pharmacokinetics in patient populations at risk of carbapenem-resistant pathogen infections.

Development of an effective meropenem/KPC-2 inhibitor combination to combat infections caused by carbapenem-resistant Klebsiella pneumoniae.

The global public health threat of antibiotic resistance continues to escalate, and necessitates the implementation of urgent measures to expand the arsenal of antimicrobial drugs. This study identified a benzoxaborane compound, namely 5-chloro-1,3-dihydro-1-hydroxy-2,1-benzoxaborole (AN2178), which can inhibit the catalytic activity of the Klebsiella pneumoniae carbapenemase (KPC-2) enzyme effectively. The efficacy of AN2718 as an inhibitor for the KPC-2 enzyme was verified through various assays, including enzyme activity assays and isothermal titration calorimetry. Results of multiple biochemical assays, minimum inhibitory concentration assays and time-killing assays also showed that binding of AN2718 to KPC-2 enabled restoration of the bactericidal effect of meropenem. The survival rate of mice infected with carbapenem-resistant, high-virulence strains increased significantly upon treatment with AN2718. Most importantly, the meropenem and AN2718 combination was effective on KPC-2 mutations such as KPC-33, which evolved clinically and exhibited resistance to ceftazidime-avibactam after clinical use for a couple of years. Comprehensive safety tests both in vitro and in vivo, such as cytotoxicity, haemolytic activity and cytochrome P450 inhibition assays, demonstrated that AN2718 was safe for clinical use. These promising data indicate that AN2718 has high potential for approval for the treatment of drug resistant-bacterial infections, including those caused by ceftazidime-avibactam-resistant strains. AN2718 can be regarded as a valuable addition to the current antimicrobial armamentarium, and a promising tool to combat antimicrobial resistance.

In vitro interactions of combinations of colistin with meropenem, rifampicin and tigecycline in colistin-resistant, biofilm-forming Klebsiella pneumoniae.

In this study, it was aimed to reveal the in vitro interactions of combinations of colistin with meropenem, rifampicin and tigecycline in colistin-resistant, biofilm-forming Klebsiella pneumonia. A total of 30 isolates, 15 of which formed biofilms and 15 did not form biofilms, were randomly selected from K. pneumoniae isolates growing in blood samples. The synergy rates of colistin-meropenem, colistin-tigecycline, colistin-rifampicin combinations in planktonic/sessile bacteria are; It was determined as 83,3%/73,3%, 66,6%/33,3%, 100%/60% respectively. Biofilm inhibitory concentration (BIC) of colistin, meropenem, tigecycline, and rifampicin significantly increased after biofilm formation. The synergistic activity seen in the sessile form was independent of the planktonic form. Although a high synergistic effect was observed in the meropenem-colistin combination on sessile bacteria, colistin had very high BIC ​​in all combinations. Large-scale studies are needed in which the number of isolates studied is large, bacterial resistance profiles are evaluated genomically, and various antimicrobial groups are included.

The interaction of the azetidine thiazole side chain with the active site loop (ASL) 3 drives the evolution of IMP metallo-ß-lactamase against tebipenem.

Imipenemase (IMP) metallo-ß-lactamases (MBLs) hydrolyze almost all available ß-lactams including carbapenems and are not inhibited by any commercially available ß-lactamase inhibitor. Tebipenem (TP) pivoxil is the first orally available carbapenem and possesses a unique bicyclic azetidine thiazole moiety located at the R2 position. TP has potent in vitro activity against Enterobacterales producing extended-spectrum and/or AmpC ß-lactamases. Thus far, the activity of TP against IMP-producing strains is understudied. To address this knowledge gap, we explored the structure activity relationships of IMP MBLs by investigating whether IMP-6, IMP-10, IMP-25, and IMP-78 [MBLs with expanded hydrolytic activity against meropenem (MEM)] would demonstrate enhanced activity against TP. Most of the Escherichia coli DH10B strains expressing IMP-1 variants displayed a ≥twofold MIC difference between TP and MEM, while those expressing VIM or NDM variants demonstrated comparable MICs. Catalytic efficiency (kcat/KM) values for the TP hydrolysis by IMP-1, IMP-6, IMP-10, IMP-25, and IMP-78 were significantly lower than those obtained for MEM. Molecular dynamic simulations reveal that V67F and S262G substitutions (found in IMP-78) reposition active site loop 3, ASL-3, to better accommodate the bicyclic azetidine thiazole side chain, allowing microbiological/catalytic activity to approach that of comparison MBLs used in this study. These findings suggest that modifying the R2 side chain of carbapenems can significantly impact hydrolytic stability. Furthermore, changes in conformational dynamics due to single amino acid substitutions should be used to inform drug design of novel carbapenems.

Three novel Enterobacter cloacae bacteriophages for therapeutic use from Ghanaian natural waters.

Infections caused by multidrug-resistant (MDR) bacteria are a growing global concern. Enterobacter cloacae complex (ECC) species are particularly adept at developing antibiotic resistance. Phage therapy is proposed as an alternative treatment for pathogens that no longer respond to antibiotics. Unfortunately, ECC phages are understudied when compared to phages of many other bacterial species. In this Ghanaian-Finnish study, we isolated two ECC strains from ready-to-eat food samples and three novel phages from natural waters against these strains. We sequenced the genomic DNA of the novel Enterobacter phages, fGh-Ecl01, fGh-Ecl02, and fGh-Ecl04, and assessed their therapeutic potential. All of the phages were found to be lytic, easy to propagate, and lacking any toxic, integrase, or antibiotic resistance genes and were thus considered suitable for therapy purposes. They all were found to be related to T4-type viruses: fGh-Ecl01 and fGh-Ecl04 to karamviruses and fGh-Ecl02 to agtreviruses. Testing of Finnish clinical ECC strains showed promising susceptibility to these novel phages. As many as 61.1% of the strains were susceptible to fGh-Ecl01 and fGh-Ecl04, and 7.4% were susceptible to fGh-Ecl02. Finally, we investigated the susceptibility of the newly isolated ECC strains to three antibiotics - meropenem, ciprofloxacin, and cefepime - in combination with the novel phages. The use of phages and antibiotics together had synergistic effects. When using an antibiotic-phage combination, even low concentrations of antibiotics fully inhibited the growth of bacteria.

Does Two-Step Infusion Improve the Pharmacokinetics/Pharmacodynamics Target Attainment of Meropenem in Critically Ill Patients?

The optimal method for administering meropenem remains controversial. This study was conducted to explore the optimal two-step infusion strategy (TIT), and to investigate whether TIT is superior to intermittent infusion therapy (IIT) and prolonged infusion therapy (PIT). A physiologically based pharmacokinetics model for critically ill patients was established and evaluated. The validated model was utilized to evaluate the pharmacokinetics/pharmacodynamics (PK/PD) target attainment of meropenem. The PK/PD target attainment of different TITs varied greatly, and the total infusion duration and the first-step dose greatly affected these values. The optimal TIT was 0.25 g (30 min) + 0.75 g (150 min) at MICs of ≤2 mg/L, and 0.25 g (45 min) + 0.75 g (255 min) at MICs of 4-8 mg/L. The PK/PD target attainment of optimal TIT, PIT, and IIT were 100 % at MICs of ≤1 mg/L. When MIC increased to 2-8 mg/L, the PK/PD target attainment of optimal TIT was similar to that of PIT and higher than IIT. In conclusion, TIT did not significantly improve the PK/PD target attainment of meropenem compared with PIT. IIT is adequate at MICs of ≤1 mg/L, and PIT may be the optimal meropenem infusion method in critically ill patients with MICs of 2-8 mg/L.

Methyl gallate attenuates virulence and decreases antibiotic resistance in extensively drug-resistant Pseudomonasaeruginosa.

Pseudomonas aeruginosa infections have become a serious threat to public health due to the increasing emergence of extensively antibiotic-resistant strains and high mortality rates. Therefore, the search for new therapeutic alternatives has become crucial. In this study, the antivirulence and antibacterial activity of methyl gallate was evaluated against six clinical isolates of extensively antibiotic-resistant P. aeruginosa. Methyl gallate exhibited minimal inhibitory concentrations of 256-384 µg/mL; moreover, the use of subinhibitory concentrations of the compound inhibited biofilm formation, swimming, swarming, proteolytic activity, and pyocyanin production. Methyl gallate plus antipseudomonal antibiotics showed a synergistic effect by reduced the MICs of ceftazidime, gentamicin and meropenem. Furthermore, the potential therapeutic effect of methyl gallate was demonstrated in an infection model. This study evidenced the antivirulence and antimicrobial activity of methyl gallate as a therapeutic alternative against P. aeruginosa.

Integration of individual preclinical and clinical anti-infective PKPD data to predict clinical study outcomes.

The AIDA randomized clinical trial found no significant difference in clinical failure or survival between colistin monotherapy and colistin-meropenem combination therapy in carbapenem-resistant Gram-negative infections. The aim of this reverse translational study was to integrate all individual preclinical and clinical pharmacokinetic-pharmacodynamic (PKPD) data from the AIDA trial in a pharmacometric framework to explore whether individualized predictions of bacterial burden were associated with the trial outcomes. The compiled dataset included for each of the 207 patients was (i) information on the infecting Acinetobacter baumannii isolate (minimum inhibitory concentration, checkerboard assay data, and fitness in a murine model), (ii) colistin plasma concentrations and colistin and meropenem dosing history, and (iii) disease scores and demographics. The individual information was integrated into PKPD models, and the predicted change in bacterial count at 24 h for each patient, as well as patient characteristics, was correlated with clinical outcomes using logistic regression. The in vivo fitness was the most important factor for change in bacterial count. A model-predicted growth at 24 h of ≥2-log10 (164/207) correlated positively with clinical failure (adjusted odds ratio, aOR = 2.01). The aOR for one unit increase of other significant predictors were 1.24 for SOFA score, 1.19 for Charlson comorbidity index, and 1.01 for age. This study exemplifies how preclinical and clinical anti-infective PKPD data can be integrated through pharmacodynamic modeling and identify patient- and pathogen-specific factors related to clinical outcomes - an approach that may improve understanding of study outcomes.

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.

ISAba1-mediated intrinsic chromosomal oxacillinase amplification confers carbapenem resistance in Acinetobacter baumannii.

Tandem amplification of carbapenemase genes increases gene copy number and enhances carbapenem resistance. These amplifications are often heterogeneous, transient, and located on plasmids, which also contribute to heteroresistance. Amplification of encoding genes is especially important for enzymes with low hydrolysis activity, which are often overlooked. Here, we reported an intrinsic oxacillinase oxaAb amplification flanked by ISAba1. The amplification is in the chromosome and contains up to 25 repeats. We provided genomic, transcriptomic, and proteomic evidence that the amplification resulted in oxacillinase overproduction. Notably, no point mutations of oxaAb were found during the amplification process. Strains of Acinetobacter baumannii with intrinsic amplified or external transformed ISAba1-oxaAb exhibited higher meropenem hydrolysis activity. Furthermore, the number of repeats in the amplification decreased gradually over a period of 21 d cultured with carbapenem withdrawal. However, upon re-exposure to meropenem, the ISAba1 flanked oxaAb responded rapidly, with repeat numbers reaching or exceeding pre-carbapenem withdrawal levels within 24 h. Taken together, these findings suggest that ISAba1-mediated gene amplification and overproduction of intrinsic low-activity oxacillinase oxaAb resulted in carbapenem resistance.

Glycine restores the sensitivity to antibiotics in multidrug-resistant bacteria.

The management of infections caused by multiresistant bacteria has become of fundamental importance for any medical practice. Glycine is the most common and the simplest non-essential amino acid in humans. Glycine is very effective in improving health and supporting growth and wellbeing of humans and animals. Instead, for many bacteria, high concentrations of glycine induce lysis or deep morphological alterations. The effect of glycine on multidrug resistant (MDR) microorganisms has not yet been extensively researched. The present study was conducted 1) to establish the effect of glycine on different nosocomial pathogens isolated during routine diagnostic investigations; 2) to determine the minimum inhibitory concentration of glycine and the type of activity performed (bacteriostatic or bactericidal) on representative isolates; 3) to test the interaction between glycine and meropenem, cefiderocol, or colistin. The data reported here show a dose-dependent activity of glycine on bacteria and its bactericidal activity on MDR bacteria. Furthermore, we found that the action of glycine restores in vitro the susceptibility of multiresistant nosocomial pathogens to the tested antibiotics.IMPORTANCEAntimicrobial resistance is a constantly growing concern throughout the world, and Italy is among the Western countries where antimicrobial resistance is most widespread. In Tuscany, carbapenemase-producing Enterobacterales are now even endemic. In this study, we challenged some resistant bacteria with a well-known molecule, glycine, the antibacterial properties of which have been known since the past century. This study could bring new insights into combining antibiotics with the simplest of all amino acids. The restoration of sensitivity to the aforementioned antibiotics by a natural compound, already used for clinical purposes, is of extreme importance in an era of proliferation of multiresistant bacteria. The in vivo use of this amino acid in evaluating its effectiveness against infections should be investigated. The low cost of this molecule can also make it easy to use even in low-income countries.