Sequential Treatment Failure With Aztreonam-Ceftazidime-Avibactam Followed by Cefiderocol Due to Preexisting and Acquired Mechanisms in a New Delhi Metallo-ß-lactamase-Producing Escherichia coli Causing Fatal Bloodstream Infection.

We report a fatal case of New Delhi metallo-ß-lactamase (NDM)-producing Escherichia coli in a bacteremic patient with sequential failure of aztreonam plus ceftazidime-avibactam followed by cefiderocol. Acquired resistance was documented phenotypically and mediated through preexisting and acquired mutations. This case highlights the need to rethink optimal treatment for NDM-producing organisms.

The growing threat of NDM-producing E. coli with penicillin-binding protein 3 mutations in the United States - is there a potential role for durlobactam?

We report identification of 5 patients with infections caused by NDM-5-producing E. coli harboring PBP3 mutations that showed reduced susceptibility to aztreonam-avibactam and cefiderocol. Durlobactam, a novel diazabicyclooctane ß-lactamase inhibitor, demonstrated minimum inhibitory concentrations ranging from 0.5 to 2 µg/mL supporting future investigations into a potential role in clinical management.

In vitro activity of meropenem-vaborbactam plus aztreonam against metallo-ß-lactamase-producing Klebsiella pneumoniae.

We evaluated the in vitro activity of meropenem-vaborbactam plus aztreonam (MEV-ATM) against 140 metallo-ß-lactamase (MBL)-producing Klebsiella pneumoniae isolates. Among them, 25 isolates (17.9%) displayed minimum inhibitory concentrations (MIC) ≥ 8 µg/mL, while 112 (80.0%) had MIC ≤ 2 µg/mL. Genomic analysis and subsequent gene cloning experiments revealed OmpK36 134-135GD-insertion and increased carbapenemase gene (blaNDM-1 and blaOXA-48-like) copy numbers are the main factors responsible for MEV-ATM non-susceptibility. Notably, MEV-ATM is actively against aztreonam-avibactam-resistant mutants due to CMY-16 mutations.

A multi-species outbreak of VIM-producing carbapenem-resistant bacteria in a burn unit and subsequent investigation of rapid development of cefiderocol resistance.

Carbapenem resistance due to metallo-ß-lactamases (MBLs) such as the Verona integron-encoded metallo-ß-lactamase (VIM) is particularly problematic due to the limited treatment options. We describe a case series of bacterial infections in a tertiary care hospital due to multi-species acquisition of a VIM gene along with our experience using novel ß-lactam antibiotics and antibiotic combinations to treat these infections. Four patients were treated with the combination of ceftazidime-avibactam and aztreonam, with no resistance to the combination detected. However, cefiderocol-resistant Klebsiella pneumoniae isolates were detected in two out of the five patients who received cefiderocol within 3 weeks of having started the antibiotic. Strain pairs of sequential susceptible and resistant isolates from both patients were analyzed using whole-genome sequencing. This analysis revealed that the pairs of isolates independently acquired point mutations in both the cirA and fiu genes, which encode siderophore receptors. These point mutations were remade in a laboratory strain of K. pneumoniae and resulted in a significant increase in the MIC of cefiderocol, even in the absence of a beta-lactamase enzyme or a penicillin-binding protein 3 (PBP3) mutation. While newer ß-lactam antibiotics remain an exciting addition to the antibiotic armamentarium, their use must be accompanied by diligent monitoring for the rapid development of resistance.

Comprehensive stability analysis of 13 ß-lactams and ß-lactamase inhibitors in in vitro media, and novel supplement dosing strategy to mitigate thermal drug degradation.

Non-clinical antibiotic development relies on in vitro susceptibility and infection model studies. Validating the achievement of the targeted drug concentrations is essential to avoid under-estimation of drug effects and over-estimation of resistance emergence. While certain ß-lactams (e.g., imipenem) and ß-lactamase inhibitors (BLIs; clavulanic acid) are believed to be relatively unstable, limited tangible data on their stability in commonly used in vitro media are known. We aimed to determine the thermal stability of 10 ß-lactams and 3 BLIs via LC-MS/MS in cation-adjusted Mueller Hinton broth at 25 and 36°C as well as agar at 4 and 37°C, and in water at -20, 4, and 25°C. Supplement dosing algorithms were developed to achieve broth concentrations close to their target over 24 h. During incubation in broth (pH 7.25)/agar, degradation half-lives were 16.9/21.8 h for imipenem, 20.7/31.6 h for biapenem, 29.0 h for clavulanic acid (studied in broth only), 23.1/71.6 h for cefsulodin, 40.6/57.9 h for doripenem, 46.5/64.6 h for meropenem, 50.8/97.7 h for cefepime, 61.5/99.5 h for piperacillin, and >120 h for all other compounds. Broth stability decreased at higher pH. All drugs were ≥90% stable for 72 h in agar at 4°C. Degradation half-lives in water at 25°C were >200 h for all drugs except imipenem (14.7 h, at 1,000 mg/L) and doripenem (59.5 h). One imipenem supplement dose allowed concentrations to stay within ±31% of their target concentration. This study provides comprehensive stability data on ß-lactams and BLIs in relevant in vitro media using LC-MS/MS. Future studies are warranted applying these data to antimicrobial susceptibility testing and assessing the impact of ß-lactamase-related degradation.

Emergence of aztreonam/avibactam and tigecycline-resistant Pseudomonas putida group Co-producing blaIMP-1, blaAFM-4 and blaOXA-1041 with a novel sequence type ST268 in Southwestern China.

OBJECTIVES: The emergence of carbapenem-resistant Pseudomonas putida (CRPP) has raised public awareness. This study investigated two strains from the Pseudomonas putida group that were resistant to carbapenem, tigecycline, and aztreonam-avibactam (ATM-AVI), with a focus on their microbial and genomic characteristics. METHODS: We assessed the antibiotic resistance profile using broth dilution, disk diffusion, and E-test methods. Efflux pump phenotype testing and real-time quantitative PCR were employed to evaluate efflux pump activity in tigecycline resistance, while polymerase chain reaction was utilized to detect common carbapenem genes. Additionally, whole-genome sequencing was performed to analyze genomic characteristics. The transferability of blaIMP-1 and blaAFM-4 was assessed through a conjugation experiment. Furthermore, growth kinetics and biofilm formation were examined using growth curves and crystal violet staining. RESULTS: Both strains demonstrated resistance to carbapenem, tigecycline, and ATM-AVI. Notably, NMP can restore sensitivity to tigecycline. Subsequent analysis revealed that they co-produced blaIMP-1, blaAFM-4, tmexCD-toprJ, and blaOXA-1041, belonging to a novel sequence type ST268. Although they were closely related on the phylogenetic tree, they exhibited different levels of virulence. Genetic environment analysis indicated variations compared to prior studies, particularly regarding the blaIMP-1 and blaAFM-4 genes, which showed limited horizontal transferability. Moreover, it was observed that temperature exerted a specific influence on their biological factors. CONCLUSION: We initially identified two P. putida ST268 strains co-producing blaIMP-1, blaAFM-4, blaOXA-1041, and tmexCD-toprJ. The resistance to tigecycline and ATM-AVI can be attributed to the presence of multiple drug resistance determinants. These findings underscore the significance of P. putida as a reservoir for novel antibiotic resistance genes. Therefore, it is imperative to develop alternative antibiotic therapies and establish effective monitoring of bacterial resistance.

Evaluation of the MTS™ aztreonam-avibactam strip (Liofilchem) on New Delhi metallo-ß-lactamase-producing Enterobacterales.

The combination of ceftazidime-avibactam (CAZ-AVI) and aztreonam (ATM) is used to treat MBL-producing Enterobacterales-related infections. The new combination aztreonam-avibactam (AZA) is currently in development. We compared results obtained with the new MIC test strip (MTS) AZA (Liofilchem) with broth microdilution method (BMD) on 41 MBL-producing Enterobacterales from 41 clinical samples. The MTS AZA was also compared to combination testing method using CAZ-AVI and ATM strips. Compared to BMD, categorical agreement (CA) was 100%. Compared with combination testing method, CA was 97.6%. The MTS AZA can be used to determine MICs levels of AZA or CAZ-AVI/ATM combinations.

Metabolomics unveil key pathways underlying the synergistic activities of aztreonam and avibactam against multidrug-resistant Escherichia coli.

PURPOSE: Aztreonam/avibactam is effective against serious infections caused by Gram-negative bacteria including Enterobacterales harboring metallo-ß-lactamases. While the utility of this combination has been established in vitro and in clinical trials, the purpose of this study is to enhance our understanding of the underlying mechanism responsible for their activities through metabolomic profiling of a multidrug-resistant Escherichia coli clinical isolate. METHODS: Metabolomic analyses of time-dependent changes in endogenous bacterial metabolites in a clinical isolate of a multidrug-resistant E. coli treated with aztreonam and avibactam were performed. E. coli metabolomes were compared at 15 min, 1 h and 24 h following treatments with either avibactam (4 mg/L), aztreonam (4 mg/L), or aztreonam (4 mg/L) + avibactam (4 mg/L). RESULTS: Drug treatment affected 326 metabolites with magnitude changes of at least 2-fold, most of which are involved primarily in peptidoglycan biosynthesis, nucleotide metabolism, and lipid metabolism. The feedstocks for peptidoglycan synthesis were depleted by aztreonam/avibactam combination; a significant downstream increase in nucleotide metabolites and a release of lipids were observed at the three timepoints. CONCLUSION: The findings indicate that the aztreonam/avibactam combination accelerates structural damage to the bacterial membrane structure and their actions were immediate and sustained compared to aztreonam or avibactam alone. By inhibiting the production of crucial cell wall precursors, the combination may have inflicted damages on bacterial DNA.

Outcomes of 23 patients diagnosed with New Delhi metallo-beta-lactamase (NDM)-producing Klebsiella pneumoniae infection treated with ceftazidime/avibactam and aztreonam at a single center in Poland.

PURPOSE: Amongst all etiologic hospital-acquired infection factors, K. pneumoniae strains producing New Delhi metallo-ß-lactamase (KP-NDM) belong to pathogens with the most effective antibiotic resistance mechanisms. Clinical guidelines recommend using ceftazidime/avibactam with aztreonam (CZA + AT) as the preferred option for NDM-producing Enterobacterales. However, the number of observations on such treatment regimen is limited. This retrospective study reports the clinical and microbiological outcomes of 23 patients with KP-NDM hospital-acquired infection treated with CZA + AT at a single center in Poland. METHODS: The isolates were derived from the urine, lungs, blood, peritoneal cavity, wounds, and peritonsillar abscess. In microbiological analysis, mass spectrometry for pathogen identification, polymerase chain reaction, or an immunochromatographic assay for detection of carbapenemase, as well as VITEK-2 system, broth microdilution, and microdilution in agar method for antimicrobial susceptibility tests were used, depending of the pathogens' nature. CZA was administered intravenously (IV) at 2.5 g every eight hours in patients with normal kidney function, and aztreonam was administered at 2 g every eight hours IV. Such dosage was modified when renal function was reduced. RESULTS: KP-NDM was eradicated in all cases. Four patients (17.4%) died: three of them had a neoplastic disease, and one - a COVID-19 infection. CONCLUSION: The combination of CZA + AT is a safe and effective therapy for infections caused by KP-NDM, both at the clinical and microbiological levels. The synergistic action of all compounds resulted in a good agreement between the clinical efficacy of CZA + AT and the results of in vitro susceptibility testing.

Reduced susceptibility to aztreonam-avibactam conferred by acquired AmpC-type ß-lactamases in PBP3-modified Escherichia coli.

PURPOSE: Carbapenemase-producing Enterobacterales are a growing threat, and very few therapeutic options remain active against those multidrug resistant bacteria. Aztreonam is the molecule of choice against metallo-beta-lactamases (MBL) producers since it is not hydrolyzed by those enzymes, but the co-production of acquired plasmidic cephalosporinases or extended-spectrum ß-lactamases leading to aztreonam resistance may reduce the efficacy of this molecule. Hence, the development of the aztreonam-avibactam (AZA) combination provides an interesting therapeutic alternative since avibactam inhibits the activity of both cephalosporinases and extended-spectrum ß-lactamases. However, structural modifications of penicillin binding protein PBP3, the target of aztreonam, may lead to reduced susceptibility to aztreonam-avibactam. METHODS: Here the impact of various plasmid-encoded AmpC-type ß-lactamases (ACC-1, ACT-7, ACT-17, CMY-2, CMY-42, DHA-1, FOX-1, and FOX-5) on susceptibility to aztreonam-avibactam was evaluated using isogenic E. coli MG1655 strains harboring insertions in PBP3 (YRIN and YRIK). The inhibitory activity of various ß-lactamase inhibitors (clavulanic acid, tazobactam, avibactam, relebactam, and vaborbactam) were also compared against these enzymes. RESULTS: Hence, we showed that reduced susceptibility to AZA was due to the combined effect of both AmpC production and amino acid insertions in PBP3. The highest resistance level was achieved in strains possessing the insertions in PBP3 in association with the production of ACT-7, ACC-1, or CMY-42. CONCLUSION: Although none of the recombinant strains tested displayed clinical resistance to aztreonam-avibactam, our data emphasize that the occurrence of such profile might be of clinical relevance for MBL-producing strains.

In vitro and in vivo activity of ceftazidime/avibactam and aztreonam alone or in combination against mcr-9, serine- and metallo-ß-lactamases-co-producing carbapenem-resistant Enterobacter cloacae complex.

PURPOSE: Enterobacteriaceae carrying mcr-9, in particularly those also co-containing metallo-ß-lactamase (MBL) and TEM type ß-lactamase, present potential transmission risks and lack adequate clinical response methods, thereby posing a major threat to global public health. The aim of this study was to assess the antimicrobial efficacy of a combined ceftazidime/avibactam (CZA) and aztreonam (ATM) regimen against carbapenem-resistant Enterobacter cloacae complex (CRECC) co-producing mcr-9, MBL and TEM. METHODS: The in vitro antibacterial activity of CZA plus ATM was evaluated using a time-kill curve assay. Furthermore, the in vivo interaction between CZA plus ATM was confirmed using a Galleria mellonella (G. mellonella) infection model. RESULTS: All eight clinical strains of CRECC, co-carrying mcr-9, MBL and TEM, exhibited high resistance to CZA and ATM. In vitro time-kill curve analysis demonstrated that the combination therapy of CZA + ATM exerted significant bactericidal activity against mcr-9, MBL and TEM-co-producing Enterobacter cloacae complex (ECC) isolates with a 100% synergy rate observed in our study. Furthermore, in vivo survival assay using Galleria mellonella larvae infected with CRECC strains co-harboring mcr-9, MBL and TEM revealed that the CZA + ATM combination significantly improved the survival rate compared to the drug-treatment alone and untreated control groups. CONCLUSION: To our knowledge, this study represents the first report on the in vitro and in vivo antibacterial activity of CZA plus ATM against CRECC isolates co-harboring mcr-9, MBL and TEM. Our findings suggest that the combination regimen of CZA + ATM provides a valuable reference for clinicians to address the increasingly complex antibiotic resistance situation observed in clinical microorganisms.

Improved synthesis and evaluation of preclinical pharmacodynamic parameters of a new monocyclic ß-lactam DPI-2016.

Monocyclic ß-lactams are stable to a number of ß-lactamases and are the focus of researchers for the development of antibacterial drugs, particularly against Enterobacterales. We recently synthesized and reported the bactericidal activity of diverse series of aztreonam appended with amidine moieties as siderophores. One of the derivatives exhibiting the highest MIC value in vitro was selected for further preclinical studies. The compound DPI-2016 was reassessed for its synthetic routes and methods that were improved to find the maximum final yields aimed at large-scale synthesis. In addition, the results of the pharmacological studies were determined with reference to aztreonam. It has been found that the compound DPI-2016 showed comparable or slightly improved ADMET as well as pharmacokinetic parameters to aztreonam. It is estimated that the compound could be a potential lead for further clinical evaluation.

Comparison of testing methods assessing the in vitro efficacy of the combination of aztreonam with avibactam on multidrug-resistant Gram-negative bacilli.

BACKGROUND: Aztreonam-avibactam (ATM-AVI) combination shows promising effectiveness on most carbapenemase-producing Gram-negatives, yet standardized antibiotic susceptibility testing (AST) methods for evaluating the combination in clinical laboratories is lacking. We aimed to evaluate different ATM-AVI AST approaches. METHODS: 96 characterized carbapenem-resistant clinical isolates belonging to 9 Enterobacterales (EB; n = 80) and P. aeruginosa (PA; n = 16) species, including 90 carbapenemase producers and 72 strains resistant to both CAZ-AVI and ATM, were tested. Paper disk elution (DE; Bio-Rad) and E-test gradient strips stacking (SS; bioMérieux) were performed for the ATM + CAZ-AVI combination. MIC Test Strip (MTS; Liofilchem) was evaluated for ATM-AVI MIC determination. Results were interpreted applying ATM clinical breakpoints of the EUCAST guidelines and compared to the broth microdilution method (Sensititre, Thermofisher). RESULTS: According to broth microdilution method, 93% of EB and 69% of PA were tested susceptible to ATM-AVI. The synergistic effect of ATM-AVI was of 95% for EB, but of only 17% for PA. The MTS method yielded higher categorical and essential agreement (CA/EA) rates for both EB (89%/91%) and PA (94%/94%) compared to SS, where the rates were 87%/83% for EB and 81%/81% for PA. MTS and SS yielded 2 and 3 major discrepancies, respectively, while 3 very major discrepancies each were observed for both methods. Concerning the DE method, CA reached 91% for EB and 81% for PA, but high number of very major discrepancies were observed for EB (n = 6; 8%) and for PA (n = 3; 19%). CONCLUSIONS: The ATM-AVI association displayed excellent in vitro activity against highly resistant clinical Enterobacterales strains. MTS method offers accurate ATM-AVI AST results, while the SS method might serve as better alternative then DE method in assessing the efficacy of ATM + CAZ-AVI combination. However, further investigation is needed to confirm the methods' ability to detect ATM-AVI resistance.

Ceftazidime-avibactam in the treatment of bacteremia due to carbapenem-resistant gram-negative bacteria in hematological patients: Experience in a single center.

INTRODUCTION: Limited experience exists with ceftazidime-avibactam (CAZ-AVI) in treating bacteremia caused by carbapenem-resistant Enterobacterales (CRE) and Pseudomonas aeruginosa (CRPA) in hematological patients. METHODS: We performed a single-center, retrospective, observational study including patients who received CAZ-AVI for bacteremia due to CRE or CRPA between 2018 and 2022. The primary outcome was 30-day survival. We conducted a multivariable analysis to identify predictors of survival. RESULTS: 56 patients were included and 57 (41 CRE and 16 CRPA) strains were isolated. 35 strains produced carbapenemase, including 25 metallo-beta-lactamase (MBL) and 10 serine-beta-lactamase. 48 patients (85.7 %) received combination therapy. All patients with MBL-CRE bacteremia (n = 24) received combination therapy with aztreonam (AZT). The susceptibility rates to CAZ-AVI were only 26.8 % (11/41) in CRE and 80.0 % (8/10) in CRPA. The 30-day survival rates were 85.0 % (34/40) in the CRE group and 81.3 % (13/16) in the CRPA group. In patients with MBL-CRE bacteremia, the 30-day survival was as high as 91.7 % (22/24) due to combination with AZT. Ceftazidime did not influence the activity of aztreonam-avibactam against MBL-CRE in-vitro. Multivariable cox analysis revealed neutropenia >14 days (P = 0.002, HR: 34.483, 95%CI: 3.846-333.333) and a higher Pitt bacteremia score (P = 0.005, HR: 2.074, 95%CI: 1.253-3.436) were risk factors for 30-day survival. CONCLUSIONS: CAZ-AVI is highly effective in treating bacteremia due to CRPA and serine-beta-lactamase CRE. The combination of avibactam with AZT is highly effective in treating bacteremia due to AZT-resistant MBL producers.

Clinical features and outcomes of infections caused by metallo-ß-lactamases producing Enterobacterales: a 3-year prospective study from an endemic area.

BACKGROUND: Metallo-ß-lactamases (MBL)-producing Enterobacterales are increasing worldwide. Our aim was to describe clinical features, treatments and outcomes of infections by MBL-Enterobacterales. METHODS: Prospective observational study conducted in the Pisa University Hospital (Jan 2019-Oct 2022) including patients with MBL-producing Enterobacterales infections. The primary outcome measure was 30-day mortality. A multivariable Cox regression analysis was performed to identify factors associated with 30-day mortality. Adjusted hazard ratio (aHR) (95% confidence intervals, CI) were calculated. RESULTS: 343 patients were included: 15 VIM- and 328 NDM-producing Enterobacterales infections. Overall, 199 (58%) were bloodstream infections, 60 (17.5%) hospital-acquired/ventilator-associated pneumonias, 60 (17.5%) complicated urinary tract infections, 13 (3.8%) intra-abdominal infections, 11 (3.2%) skin and soft tissue infections. Thirty-day mortality was 29.7%. Thirty-two patients did not receive in vitro active antibiotic therapy, 215/343 (62.7%) received ceftazidime-avibactam (CZA) plus aztreonam (ATM), 33/343 (9.6%) cefiderocol-containing regimens, 26/343 (7.6%) colistin-containing regimens and 37 (10.8%) other active antibiotics. On multivariable analysis, septic shock (aHR 3.57, 95% CI 2.05-6.23, p<0.001) and age (aHR 1.05, 95% CI 1.03-1.08, p<0.001) were independently associated with 30-day mortality, while in vitro active antibiotic therapy within 48 hours from infection (aHR 0.48, 95% CI 0.26-0.8, p=0.007) and source control (aHR 0.43, 95% CI 0.26-0.72, p=0.001) were protective factors. Sensitivity analysis showed that CZA plus ATM compared to colistin was independently associated with reduced 30-day mortality (aHR 0.39, 95% CI 0.18-0.86, p=0.019). Propensity score analyses confirmed these findings. CONCLUSIONS: MBL-CRE infections are associated with high 30-day mortality rates. Patients with MBL-producing Enterobacterales infections should received early active antibiotic therapy.

Rapid Aztreonam/Avibactam NP test for detection of aztreonam/avibactam susceptibility/resistance in Enterobacterales.

Aztreonam-avibactam (AZA), a newly developed ß-lactam/ß-lactamase inhibitor combination, is a treatment option for infections due to carbapenem-resistant Enterobacterales (CRE), including metallo-ß-lactamase producers, regardless of additional production of broad-spectrum serine-ß-lactamases. However, AZA-resistance has already been reported in Enterobacterales and its early detection could be a valuable tool for faster and more accurate clinical decision-making. We therefore developed a rapid culture-based test for the identification of AZA resistance among multidrug-resistant Enterobacterales. The Rapid Aztreonam/Avibactam NP test is based on resazurin reduction when bacterial growth occurs in the presence of AZA at 8/4 µg/mL (protocol 1) or 12/4 µg/mL (protocol 2). Given the absence of guidelines on AZA susceptibility testing, two tentative breakpoints were indeed used to categorize AZA-susceptible isolates: ≤4 µg/mL in protocol 1 and ≤ 8 µg/mL in protocol 2. Bacterial growth was visually detectable by a blue-to-purple or blue-to-pink color change of the medium. A total of 78 enterobacterial isolates (among which 34 AZA-resistant and 13 AZA-resistant according to protocols 1 and 2, respectively) were used to evaluate the test performance using protocol 1 or protocol 2. The sensitivity and specificity of the test were found to be 100% and 97.7%, respectively, following protocol 1 and 100% and 100%, respectively, following protocol 2, in comparison with broth microdilution. All results were obtained within 4.5 hours corresponding to a time saving of ca. 14 hours compared with currently available methods for AZA susceptibility testing. The Rapid Aztreonam/Avibactam NP test is rapid, highly sensitive, specific, easily interpretable, and easy to implement in routine.

Multicenter Evaluation of an MIC-Based Aztreonam and Ceftazidime-Avibactam Broth Disk Elution Test.

Due to limited therapeutic options, there is a clinical need to assess the in vitro activity of the combination of aztreonam (ATM) and ceftazidime-avibactam (CZA) to guide the therapeutic management of multidrug-resistant (MDR) Gram-negative organism infections. We set out to develop a practical MIC-based broth disk elution (BDE) method to determine the in vitro activity of the combination ATM-CZA using readily available supplies and compare it to reference broth microdilution (BMD). For the BDE method, a 30-µg ATM disk, a 30/20-µg CZA disk, both disks in combination, and no disks were added to 4 separate 5-mL cation-adjusted Mueller-Hinton broth (CA-MHB) tubes, using various manufacturers. Three testing sites performed both BDE and reference BMD testing of bacterial isolates in parallel from a single 0.5 McFarland standard inoculum and after overnight incubation, assessed them for growth (not susceptible) or no growth (susceptible) at a final concentration of 6/6/4 µg/mL ATM-CZA. During the first phase, the precision and accuracy of the BDE were analyzed by testing 61 Enterobacterales isolates at all sites. This testing yielded 98.3% precision between sites, with 98.3% categorical agreement and 1.8% major errors (ME). During the second phase, at each site, we evaluated unique, clinical isolates of metallo-ß-lactamase (MBL)-producing Enterobacterales (n = 75), carbapenem-resistant Pseudomonas aeruginosa (n = 25), Stenotrophomonas maltophilia (n = 46), and Myroides sp. (n = 1). This testing resulted in 97.9% categorical agreement, with 2.4% ME. Different results were observed for different disk and CA-MHB manufacturers, requiring a supplemental ATM-CZA-not-susceptible quality control organism to ensure the accuracy of results. The BDE is a precise and effective methodology for determining susceptibility to the combination ATM-CZA.

Chronic inhaled antibiotic therapy in people with cystic fibrosis with Pseudomonas aeruginosa infection in Germany.

BACKGROUND: Several clinical guidelines recommend chronic inhaled therapy for pwCF (people with cystic fibrosis) and chronic Pseudomonas aeruginosa infection of the lungs. METHODS: To demonstrate what kind of therapy regimens are used in Germany, we retrospectively analysed chronic inhaled antibiotic therapy within the cohort of the German CF Registry in 2020. For comparison we also analysed the use of inhaled antibiotics in pwCF with intermittent Pseudomonas or without Pseudomonas infection. RESULTS: A total of 1960 pwCF had chronic P. aeruginosa infection and were retrospectively evaluated. Almost 90% (n = 1751) received at least one inhaled antibiotic. The most commonly used inhaled antibiotic was colistin solution for inhalation (55.2%), followed by aztreonam solution for inhalation (32.6%) and tobramycin solution for Inhalation (30%). Almost 56% of adults and 44% of children alternated two antibiotics for inhalation. In children, alternating colistin + tobramycin was the most often used regimen. In adults, only 23% used colistin + tobramycin; there was a wide range of treatment regimens among adults using two inhaled antibiotics alternately. 2456 pwCF had no Pseudomonas infection, but almost 24% had a chronic inhaled antibiotic therapy, while 56% of 361 pwCF and intermittent chronic Pseudomonas infection had a chronic inhaled antibiotic therapy. CONCLUSION: In all three groups the most commonly used inhaled antibiotic was colistin solution for inhalation. Almost 56% of adults and 44% of children with chronic Pseudomonas infection alternated two antibiotics for inhalation. It will be interesting to see how the introduction of the highly effective modulator elexacaftor/tezacaftor/ivacaftor will change the use of inhaled antibiotics.

In vitro activity of aztreonam-avibactam against Enterobacterales isolates collected in Latin America, Africa/Middle East, Asia, and Eurasia for the ATLAS Global Surveillance Program in 2019-2021.

This study aimed to report reference method antimicrobial susceptibility results for 24,937 recent (2019-2021) clinical isolates of Enterobacterales from 27 countries in Latin America, Eurasia, Africa/Middle East, and Asia with a focus on the investigational combination aztreonam-avibactam against metallo-ß-lactamase (MBL) isolates. Antimicrobial susceptibility testing was performed by the CLSI broth microdilution methodology. Minimum inhibitory concentrations (MICs) were interpreted using the CLSI (2022) breakpoints for all agents except aztreonam-avibactam (provisional pharmacokinetic/pharmacodynamic susceptible breakpoint, ≤ 8 mg/L) and tigecycline (US-FDA). Molecular testing for ß-lactamase genes was performed on isolates with meropenem MICs ≥ 2 mg/L, ceftazidime-avibactam MICs ≥ 16 mg/L, and/or aztreonam-avibactam MICs ≥ 16 mg/L, and 50% of isolates of Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Klebsiella variicola, and Proteus mirabilis testing with ceftazidime and/or aztreonam MICs ≥ 2 mg/L. Aztreonam-avibactam inhibited 99.8% of all Enterobacterales at ≤ 8 mg/L (MIC90, 0.25 mg/L) and maintained activity against phenotypically resistant subsets of multidrug-resistant (MDR) (99.5% susceptible), extensively drug-resistant (XDR) (98.7%), and carbapenem-resistant Enterobacterales (CRE) (99.1%) isolates. At ≤ 8 mg/L, aztreonam-avibactam inhibited 100%, 99.6%, 99.6%, and 98.8% of KPC-, OXA-48-like-, ESBL-, and MBL-carrying isolates, respectively. MBL-positive isolates were most prevalent in India (20.5%), Guatemala (13.8%), and Jordan (13.2%). No differences in the activity of aztreonam-avibactam were observed across the global regions evaluated. At a concentration of ≤ 8 mg/L, aztreonam-avibactam inhibited almost all Enterobacterales collected from developing countries, including MBL-producing isolates. The widespread dissemination of MBLs among Enterobacterales highlights the unmet need for new agents such as aztreonam-avibactam for the treatment of CRE infections.

First case of bloodstream infection caused by NDM-positive Escherichia hermannii.

BACKGROUND: Escherichia hermannii (E. hermanni) is always accompanied by other bacterial infections in humans. In previous reports, most E. hermannii-related infections were caused by sensitive strains. Here, for the first time, we report the case of a patient with New Delhi metallo-ß-lactamase (NDM)-positive E. hermannii bloodstream infection. CASE PRESENTATION: The patient was a 70-year-old male admitted to our hospital due to a 4-day fever, with a history of malignant tumor, liver cirrhosis, and chronic obstructive pulmonary disease. After admission, his blood culture tested positive for E. hermannii. The drug resistance analysis showed positive for NDM resistance, with susceptibility to aztreonam, levofloxacin, and amikacin. The blood culture turned negative after 8 days of aztreonam treatment. The patient's symptoms improved, and he was discharged after 14 days of hospitalization. CONCLUSIONS: This is the first report of a bloodstream infection caused by an NDM-positive E. hermannii strain. The anti-infection regimen used in this case provides a new reference regimen for clinical practice.