Search Results (87)

Introduction: The combination of ceftazidime−avibactam (CAZ-AVI) with aztreonam (ATM) may be an option for the treatment of infections due to metallo-β-lactamases (MBLs) producing bacteria, as recommended by current guidelines. MBLs protect the pathogen from any available β-lactam/β-lactamase inhibitor (BL/BLI). Moreover, in vitro and clinical data suggest that double carbapenem therapy (DCT) may be an option for such infections. Materials and Methods: This retrospective study was conducted in two mixed intensive care units (ICUs) at the University Hospital of Larissa, Thessaly, Greece, and the General Hospital of Larissa, Thessaly, Greece, during a three-year period (2022−2024). Mechanically ventilated patients with bloodstream infection (BSI) caused by K. pneumoniae resistant to all BL/BLI combinations were studied. Patients were divided into three groups: in the first, patients were treated with CAZ-AVI + ATM; in the second, with DCT; and in the third, with antibiotics other than BL/BLIs that presented in vitro susceptibility. The primary outcome of the study was the change in Sequential Organ Failure Assessment (SOFA) score between the onset of infection and the fourth day of antibiotic treatment. Secondary outcomes were SOFA score evolution during the treatment period, total duration of mechanical ventilation (MV), ICU length of stay (LOS), and ICU mortality. Results: A total of 95 patients were recruited. Among them, 23 patients received CAZ-AVI + AZT, 22 received DCT, and 50 patients received another antibiotic regimen which was in vitro active against the pathogen. The baseline characteristics were similar. The mean (SE) overall age was 63.2 (1.3) years. Mean (SE) Acute Physiology and Chronic Health Evaluation II (APACHE II) and SOFA scores were 16.3 (0.6) and 7.6 (0.3), respectively. The Charlson Index was similar between groups. The control group presented a statistically lower SOFA score on day 4 compared to the other two groups [mean (SE) 8.9 (1) vs. 7.4 (0.9) vs. 6.4 (0.5) for CAZ-AVI + ATM, DCT and control group, respectively (p = 0.045)]. The duration of mechanical ventilation, ICU LOS, and mortality were similar between the groups (p > 0.05). Comparison between survivors and non-survivors revealed that survivors had a lower SOFA score on the day of BSI, higher PaO₂/FiO₂ ratio, higher platelet counts, and lower lactate levels (p < 0.05). Septic shock was more frequent among non-survivors (60.3%) in comparison to survivors (27%) (p = 0.0015). Independent factors for mortality were PaO₂/FiO₂ ratio and lactate levels (p < 0.05). None of the antibiotic regimens received by the patients was independently associated with survival. Conclusions: Treatment with CAZ-AVI + ATM or DCT may offer similar clinical outcomes for patients suffering from BSI caused by K. pneumoniae strains resistant to all available BL/BLIs. However, larger studies are required to confirm the findings. Full article

Cefepime-enmetazobactam is a novel β-lactam/β-lactamase inhibitor combination showing good activity against multidrug-resistant (MDR) Gram-negative bacteria producing a variety of β-lactamases. In this systematic review, we aimed to evaluate the available data on resistance to this drug. We performed a thorough search of four databases (Embase, PubMed, Scopus, and Web of Science), as well as backward citation searching, to identify studies containing data on resistance to cefepime-enmetazobactam. The data were extracted and analyzed according to the breakpoints established by the European Committee on Antimicrobial Susceptibility Testing (EUCAST) and the Food and Drug Administration (FDA), or the specific breakpoints reported by the authors of the respective studies. Analysis based on the type of lactamases produced by the isolates was also performed. Ten studies reported in vitro susceptibility testing and mechanisms of antimicrobial resistance. The total number of isolates was 15,408. The activity of cefepime-enmetazobactam against β-lactamase-producing isolates was variable. The resistance of the studied extended-spectrum β-lactamase (ESBL)-producing and ampicillin C β-lactamase (AmpC)-producing isolates was low (0–2.8% and 0%, respectively). The resistance was higher among oxacillinase-48 β-lactamase (OXA-48)-producing and Klebsiella pneumoniae carbapenemase (KPC)-producing isolates (3.4–13.2% and 36.7–57.8%, respectively). High resistance was noted among metallo-β-^lactamase (MBL)-producing isolates (reaching 87.5% in one study), especially those producing New Delhi metallo-β-lactamase (NDM) and Verona integron-encoded metallo-β-lactamase (VIM), which had the highest rates of resistance. The high activity of cefepime-enmetazobactam against Enterobacterales and selected lactose non-fermenting Gram-negative pathogens, including ESBL-producing and AmpC-producing isolates, makes it a potential carbapenem-sparing agent. The drug should be used after in vitro antimicrobial susceptibility testing in patients with infections caused by OXA-48, KPC, and MBL-producing isolates. Full article

Introduction: Carbapenem-resistant Klebsiella pneumoniae (CRKP) represents a critical public health threat due to its rapid nosocomial dissemination, limited therapeutic options, and elevated mortality rates. This study aimed to characterize the epidemiology, carbapenemase profiles, and antimicrobial susceptibility patterns of CRKP isolates, as well as the clinical features and outcomes observed in infected or colonized patients. Materials and Methods: We conducted a retrospective analysis of clinical and microbiological data from patients with CRKP infections or colonization admitted between January 2023 and January 2024. Descriptive statistics were used to assess prevalence, resistance patterns, and patient outcomes. Two binary logistic regression models were applied to identify independent predictors of sepsis and in-hospital mortality. Results: Among 89 CRKP isolates, 45 underwent carbapenemase typing. More than half were metallo-β-lactamase (MBL) producers, with 44.4% co-harbouring NDM and OXA-48-like enzymes. Surgical intervention was associated with a significantly lower risk of sepsis (p < 0.01) and in-hospital mortality (p = 0.045), whereas intensive care unit (ICU) stay was a strong predictor of both outcomes. ICU admission conferred a 10-fold higher risk of sepsis (95%Cl 2.4–41.0) and a 40.8-fold higher risk of in-hospital death (95% Cl 3.5–473.3). Limitations: This single-center retrospective study included a limited number of isolates in certain groups. Additionally, cefiderocol (FDC) susceptibility was assessed by disk diffusion rather than by the broth microdilution method. Conclusions: Our study underscores the increasing prevalence of metallo-beta-lactamase-producing CRKP, particularly strains harbouring dual carbapenemases. Timely recognition of high-risk patients, combined with the implementation of targeted infection control measures and the integration of novel therapeutic options, is crucial to optimize clinical management and reduce mortality associated with CRKP. Full article

Background/objectives: Proteus mirabilis is a frequent causative agent of urinary and wound infections in both community and hospital settings. It develops resistance to expanded-spectrum cephalosporins (ESCs) due to the production of extended-spectrum β-lactamases (ESBLs) or plasmid-mediated AmpC β-lactamases (p-AmpCs). Recently, carbapenem-resistant isolates of P. mirabilis emerged due to the production of carbapenemases, mostly belonging to Ambler classes B and D. Here, we report an outbreak of infections due to carbapenem-resistant P. mirabilis that were observed in a psychiatric hospital in Zagreb, Croatia. The characteristics of ESBL and carbapenemase-producing P. mirabilis isolates, associated with an outbreak, were analyzed. Materials and methods: The antibiotic susceptibility testing was performed by the disk-diffusion and broth dilution methods. The double-disk synergy test (DDST) and inhibitor-based test with clavulanic and phenylboronic acid were applied to screen for ESBLs and p-AmpCs, respectively. Carbapenemases were screened by the modified Hodge test (MHT), while carbapenem hydrolysis was investigated by the carbapenem inactivation method (CIM) and EDTA-carbapenem-inactivation method (eCIM). The nature of the ESBLs, carbapenemases, and fluoroquinolone-resistance determinants was investigated by PCR. Plasmids were characterized by PCR-based replicon typing (PBRT). Selected isolates were subjected to molecular characterization of the resistome by an Inter-Array Genotyping Kit CarbaResisit and whole-genome sequencing (WGS). Results: In total, 20 isolates were collected and analyzed. All isolates exhibited resistance to amoxicillin alone and when combined with clavulanic acid, cefuroxime, cefotaxime, ceftriaxone, cefepime, imipenem, ceftazidime–avibactam, ceftolozane–tazobactam, gentamicin, amikacin, and ciprofloxacin. There was uniform susceptibility to ertapenem, meropenem, and cefiderocol. The DDST and combined disk test with clavulanic acid were positive, indicating the production of an ESBL. The MHT was negative in all except one isolate, while the CIM showed moderate sensitivity, but only with imipenem as the indicator disk. Furthermore, eCIM tested positive in all of the CIM-positive isolates, consistent with a metallo-β-lactamase (MBL). PCR and sequencing of the selected amplicons identified VIM-1 and VIM-4. The Inter-Array Genotyping Kit CarbaResist and WGS identified β-lactam resistance genes bla_VIM, bla_CTX-M-15, and bla_TEM genes; aminoglycoside resistance genes aac(3)-IId, aph(6)-Id, aph(3″)-Ib, aadA1, armA, and aac(6′)-IIc; as well as resistance genes for sulphonamides sul1 and sul2, trimethoprim dfr1, chloramphenicol cat, and tetracycline tet(J). Conclusions: This study revealed an epidemic spread of carbapenemase-producing P. mirabilis in two wards in a psychiatric hospital. Due to the extensively resistant phenotype (XDR), therapeutic options were limited. This is the first report of carbapenemase-producing P. mirabilis in Croatia. Full article

This systematic review assessed the global epidemiology of metallo-β-lactamase (MBL)-producing Acinetobacter clinical isolates and the associated antimicrobial resistance. A total of 475 relevant articles from the Cochrane Library, Google Scholar, PubMed, Scopus, and Web of Science were identified and screened as potentially eligible articles. Data from 85 articles were extracted for the analysis. Most reports on MBL-producing Acinetobacter clinical isolates originated from Asia [68/85 (80%) studies] and Africa [14/85 (16.5%) studies]. There were also scarce reports from Europe and America. The bla_VIM (in 31 studies), bla_IMP (in 29 studies), and bla_NDM (in 21 studies) genes were the most commonly identified genes. In 22 out of 28 (78.6%) studies with comparable data, the proportions of MBL-producing pathogens detected using phenotypic methods were numerically higher than those using genotypic methods. MBL-producing Acinetobacter isolates showed high resistance (up to 100%) to several antibiotic classes, including carbapenems, cephalosporins, fluoroquinolones, and monobactams. However, they showed low resistance to colistin [ranging from 0% (in six studies) to 14.3% (in one study)] and to tigecycline [0% (in three studies)]. No risk of bias assessment was conducted. The findings emphasize the global spread of MBL-producing Acinetobacter and the need for enhanced antimicrobial stewardship, infection control measures, and surveillance. Full article

Accurate antimicrobial susceptibility testing (AST) of cefiderocol remains a diagnostic challenge, especially in infections caused by metallo-β-lactamase (MBL)-producing Klebsiella pneumoniae. While disk diffusion offers a cost-effective alternative to broth microdilution, it is highly sensitive to factors such as media composition and the presence of atypical colony morphology. The objective of this study was to evaluate how different agar media and interpretations of isolated colonies affect the performance and reliability of cefiderocol AST by disk diffusion. A total of 50 clinical K. pneumoniae MBL isolates were tested using disk diffusion on Columbia with blood, MacConkey, and chromogenic agars from three manufacturers. Inhibition zones were compared with MICs from broth microdilution. Statistical analyses included paired t-tests and Spearman correlation to assess media effects and zone morphology impact. Variability in inhibition zone diameters was observed between media, notably with chromogenic agar. The most consistent results were obtained using Graso Biotech and Thermo Fisher Columbia with blood agar. Isolated colonies were observed in over half the samples and, depending on how they were interpreted, led to major changes in classification accuracy. Up to 64% of results fell into the EUCAST area of technical uncertainty (ATU), and categorical agreement varied across media and interpretive criteria. Disk diffusion for cefiderocol may be used in resource-limited settings but only if rigorously standardized using validated media, consistent zone reading, and ATU-aware interpretive strategies. In borderline cases or when morphological anomalies are present, broth microdilution should be considered the sole reliable method. Clinical microbiologists are advised to exercise caution with ambiguous results and seek expert or confirmatory testing when needed. Full article

Diabetic foot infections (DFIs) are a severe complication of diabetes and are increasing in prevalence globally. The microbiology of DFIs exhibits significant regional variation, with Acinetobacter baumannii frequently emerging as the predominant pathogen. This study aimed to investigate the microbiological profile of A. baumannii in DFIs of different Wagner grades. Pus and tissue specimens from 480 diabetic patients treated for DFIs between September 2016 and August 2019 were collected, and antimicrobial susceptibility testing was performed. Multiplex PCR was conducted to amplify extended spectrum β-lactamase (ESBL) and metallo-β-lactamase (MBL) genes. A. baumannii had a prevalence of 14.58% in DFIs, with 100% resistance to cephalosporins. Among the 70 A. baumannii isolates, 19 (27.14%) were ESBL producers and 43 (61.43%) were MBL producers. blaTEM was the most prevalent gene (52.94%) in ESBL producers; blaNDM-1 was the most prevalent gene (52.94%) in MBL producers. Our findings highlight the need for regular antimicrobial susceptibility testing, molecular surveillance, and robust antimicrobial stewardship programmes to effectively manage A. baumannii DFIs and mitigate their resistance. Full article

Pseudomonas aeruginosa, a Gram-negative, motile bacterium, may cause significant infections in both community and hospital settings, leading to substantial morbidity and mortality. This opportunistic pathogen can thrive in various environments, making it a public health concern worldwide. P. aeruginosa’s genomic pool is highly dynamic and diverse, with a pan-genome size ranging from 5.5 to 7.76 Mbp. This versatility arises from its ability to acquire genes through horizontal gene transfer (HGT) via different genetic elements (GEs), such as mobile genetic elements (MGEs). These MGEs, collectively known as the mobilome, facilitate the spread of genes encoding resistance to antimicrobials (ARGs), resistance to heavy metals (HMRGs), virulence (VGs), and metabolic functions (MGs). Of particular concern are the acquired carbapenemase genes (ACGs) and other β-lactamase genes, such as classes A, B [metallo-β-lactamases (MBLs)], and D carbapenemases, which can lead to increased antimicrobial resistance. This review emphasizes the importance of the mobilome in understanding antimicrobial resistance in P. aeruginosa. Full article

The growing problem of infections due to pathogens with antimicrobial resistance, especially Gram-negative bacteria, has led to the development of new β-lactam/β-lactamase inhibitor combination antibiotics. During the last 2 years from the writing of this article, cefepime/enmetazobactam, aztreonam/avibactam, and sulbactam/durlobactam were approved for use in clinical practice. Cefepime/enmetazobactam targets extended-spectrum β-lactamase (ESBL)-producing Pseudomonas aeruginosa and Enterobacterales. It is indicated for the treatment of patients with complicated urinary tract infections, including pyelonephritis, in Europe and the USA, and also for hospital-acquired pneumonia, ventilator-associated pneumonia, and bacteremia associated with those infections (only in Europe). The antimicrobial spectrum of aztreonam/avibactam includes carbapenem-resistant Enterobacterales. Aztreonam/avibactam is indicated for the treatment of adult patients who suffer from complicated intra-abdominal infections, complicated urinary tract infections including pyelonephritis, hospital-acquired pneumonia, and ventilator-associated pneumonia due to aerobic Gram-negative infections with limited therapeutic options. Sulbactam/durlobactam, a combination of 2 β-lactamase inhibitors, is indicated for the treatment of adult patients with hospital-acquired bacterial pneumonia and ventilator-associated bacterial pneumonia due to the Acinetobacter baumannii–calcoaceticus complex [including carbapenem-resistant Acinetobacter baumannii (CRAB) infections]. Full article

Background/Objectives: Carbapenem-resistant Pseudomonas aeruginosa (CRPA) is an important pathogen associated with high mortality and treatment failure rates. We aimed to assess the susceptibility of CRPA to antipseudomonal agents, identify its resistance mechanisms, and evaluate clinical outcomes in a sample of CRPA isolates. Methods: This was an in vitro study of a clinical isolate of CRPA from hospitalized patients with CRPA infection and a retrospective observational study of these patients, who were diagnosed between 14 February 2021 and 10 August 2023 at Songklanagarind Hospital in Songkhla, Thailand. In vitro experiments were conducted to determine the minimum inhibitory concentrations (MICs) of the antipseudomonal agents using the broth microdilution method. Resistance mechanisms were assessed using the modified carbapenem inactivation method, combined disk tests, and quantitative real-time reverse transcription polymerase chain reaction. Results: A total of 140 CRPA isolates were analyzed. Both traditional and novel β-lactams had high MICs. The most common resistance mechanism was the upregulation of the MexAB-OprM efflux pump (81.3%), followed by the downregulation of the OprD porin (48.9%) and metallo-β-lactamase (MBL) production (45.0%), and the overexpression of bla_AmpC (41.0%). The 30-day all-cause mortality rate was 30.5%. The risk factors associated with 30-day mortality included a Charlson Comorbidity Index of ≥5 (OR: 3.43; 95% CI: 1.07–10.99; p = 0.03), sepsis (OR: 10.62; 95% CI: 1.26–89.44; p = 0.03), and septic shock (OR: 4.39; 95% CI: 1.67–11.55; p < 0.01). In contrast, receiving active documented therapy was significantly associated with reduced mortality (OR: 0.17; 95% CI: 0.04–0.74; p = 0.01). Conclusions: This study revealed higher MIC values of all β-lactams for CRPA, while colistin and amikacin remained effective. The resistance mechanisms included MexAB-OprM overexpression, OprD downregulation, MBL production, and bla_AmpC overexpression, with a higher prevalence of MBL than in other regions of Thailand. High 30-day mortality was associated with comorbidities, sepsis, and septic shock, but active therapy reduced mortality. Full article

In recent years, resistance of Klebsiella pneumoniae to the clinical last-resort drugs carbapenem and tigecycline has intensified, including Metallo-β-Lactamase-producing K. pneumoniae (MBL-KP), which demonstrated resistance to ceftazidime-avibactam (CZA), posing a significant public health threat. This study focused on the carbapenems, CZA, and tigecycline resistance mechanisms of MBL-producing Carbapenem-resistant K. pneumoniae (MBL-CRKP). A retrospective study and genomic epidemiological analysis of Carbapenem-resistant K. pneumoniae (CRKP) strains isolated from Yangzhou City, Jiangsu Province, China, between 2016 and 2023 was conducted. The detection rate of CRKP in Yangzhou City has increased significantly in recent years, with five strains carrying the Metallo-β-Lactamases (MBLs) gene, all of which exhibited resistance to carbapenems and CZA. Two strains even showed reduced susceptibility to tigecycline, with one harboring tmexCD2-toprJ2. Moreover, three CRKP strains carrying both bla_KPC-2 and bla_NDM-1/bla_NDM-29 genes were identified. Plasmids carrying MBL genes can horizontally transfer, leading to the spread of resistance, thus further exacerbating the difficulty of clinical treatment and the spread of resistance. In conclusion, this study not only revealed the resistance of MBL-CRKP strains to clinical last-resort therapeutic drugs but also explored the resistance mechanism and horizontal transfer through genomic analysis. Moreover, this study also suggested that microbial drug resistance surveillance should be conducted from the perspective of “one health” in the future to combat this global health challenge. Full article

Background: Combination therapy with antibiotics and phages has been suggested to increase the antibacterial activity of both antibiotics and phages. We tested the in vitro activity of five antibiotics belonging to different classes in combination with lytic bacteriophages against multidrug-resistant metallo-β-lactamase (MBL)-producing Pseudomonas aeruginosa isolates. Material/Methods: A total of 10 non-repetitive well-characterized MBL-producing P. aeruginosa isolates (5 NDM, 5 VIM) co-resistant to aminoglycosides and quinolones were used. Phage–antibiotic interactions were assessed using an ISO-20776-based broth microdilution checkerboard assay in 96-well microtitration plates. Two-fold dilutions of colistin (8–0.125 mg/L), ciprofloxacin, meropenem, aztreonam, and amikacin (256–4 mg/L) were combined with ten-fold dilutions of five different phages (5 × 10⁹–5 × 10⁰ PFU/mL) belonging to Pakpunavirus, Phikzvirus, Pbunavirus, and Phikmvvirus genus. Plates were incubated at 35 ± 2 °C for 24 h, and the minimum inhibitory concentration of antibiotics (MIC_A) and phages (MIC_P) were determined as the lowest drug and phage concentration, resulting in <10% growth based on photometric reading at 550 nm. Interactions were assessed based on the fractional inhibitory concentration index (FICi) of three independent replicates and clinical relevance based on the reversal of phenotypic resistance. The statistical significance of each drug alone and in combination with phages was assessed using GraphPad Prism 8.0. Results: Synergistic and additive interactions were found for 60–80% of isolates for all drugs. FICis were statistically significantly lower than 0.5 for colistin (p = 0.005), ciprofloxacin (p = 0.02), meropenem (p = 0.003), and amikacin (p = 0.002). Interactions were found at clinically achievable concentrations for colistin, meropenem, and amikacin, and a reversal of phenotypic resistance was observed for most strains (63–64%) for amikacin and meropenem. Antagonism was found for few isolates with all antibiotics tested. Phage vB_PaerM_AttikonH10 and vB_PaerP_AttikonH4 belonging to Phikzvirus and Phikmvvirus genus, respectively, showed either synergistic (FICi ≤ 0.35) or additive effects with most antibiotics tested. Conclusions: Synergy was observed for most drugs and phages with amikacin, showing strong synergy and reversal of phenotypic resistance against most isolates. Taking into account the wide utility of jumbo phages obtained, the findings of vB_PaerM_AttikonH10 in combination with different classes of antibiotics can enhance the activity of currently ineffective antibiotics against MBL-producing P. aeruginosa isolates. Full article

The management of infectious diseases has proven to be a daunting task for clinicians worldwide, and the rapid development of antibiotic resistance among Gram-negative bacteria is making it even more challenging. The first-line therapy is empirical, and it most often comprises β-lactam antibiotics. Among Gram-negative bacteria, Proteus mirabilis, an important community and hospital pathogen associated primarily with urinary tract and wound infection, holds a special place. This review’s aim was to collate and examine recent studies investigating β-lactam resistance phenotypes and mechanisms of Proteus species and the global significance of its β-lactam resistance evolution. Moreover, the genetic background of resistance traits and the role of mobile genetic elements in the dissemination of resistance genes were evaluated. P. mirabilis as the dominant pathogen develops resistance to expanded-spectrum cephalosporins (ESC) by producing extended-spectrum β-lactamases (ESBL) and plasmid-mediated AmpC β-lactamases (p-AmpC). β-lactamase-mediated resistance to carbapenems in Enterobacterales, including Proteus spp., is mostly due to expression of carbapenemases of class A (KPC); class B (metallo-β-lactamases or MBLs of IMP, VIM, or NDM series); or class D or carbapenem-hydrolyzing oxacillinases (CHDL). Previously, a dominant ESBL type in P. mirabilis was TEM-52; yet, lately, it has been replaced by CTX-M variants, particularly CTX-M-14. ESC resistance can also be mediated by p-AmpC, with CMY-16 as the dominant variant. Carbapenem resistance in Proteus spp. is a challenge due to its intrinsic resistance to colistin and tigecyclin. The first carbapenemases reported belonged to class B, most frequently VIM-1 and NDM-5. In Europe, predominantly France and Belgium, a clonal lineage positive for OXA-23 CHDL spreads rapidly undetected, due to its low-level resistance to carbapenems. The amazing capacity of Proteus spp. to accumulate a plethora of various resistance traits is leading to multidrug or extensively drug-resistant phenotypes. Full article

Background/Objectives: Metallo-β-lactamases (MBLs) in Enterobacterales and other Gram-negative organisms pose significant public health threats due to their association with multidrug resistance (MDR). Although aztreonam (AZT) can target MBL-producing organisms, its efficacy is compromised in organisms expressing additional β-lactamases that inactivate it. Combining AZT with the β-lactamase inhibitor avibactam (AVI) may restore its activity against MBL-producing isolates. Methods: AZT-AVI, along with other clinically relevant antimicrobials, was tested against thirteen MBL-producing clinical isolates of Enterobacterales (nine Klebsiella pneumoniae, three Enterobacter cloacae, and one Providencia stuartii) using whole-genome sequencing (WGS) for genetic characterization. Results: AZT-AVI demonstrated full susceptibility across all isolates, whereas aztreonam alone was ineffective. The newer β-lactam/β-lactamase inhibitor combinations imipenem/relebactam and meropenem/vaborbactam were inactive in 100% and 92.3% of isolates, respectively. WGS-based analysis revealed multiple resistance mechanisms consistent with MDR phenotypes, including high-risk K. pneumoniae clones (ST147 and ST11). Conclusions: AZT-AVI is effective against MDR MBL-producing Enterobacterales, highlighting its therapeutic potential for challenging infections. While WGS does not replace phenotypic testing, it provides valuable insights for antimicrobial stewardship and the monitoring of resistance gene dissemination. Full article

Background/Objectives: Previously, we reported that 3-O-alkyl difluoroquercetins (di-F-Q) potentiates the antimicrobial activity of aztreonam (ATM) against metallo-β-lactamase (MBL)-producing P. aeruginosa through simultaneous inhibition of MBLs and efflux pumps. However, the ATM-potentiating activity of the 3-O-alkyl di-F-Q was observed only at high and potentially toxic concentrations (32 mg/L). Methods: As both MBLs and efflux pumps reside in the periplasm of Gram-negative bacteria, their inhibitors should accumulate in the periplasmic space. However, the outer membrane porins, the major entry pathway in Gram-negative bacteria, allow the passive diffusion of hydrophilic polar molecules across the outer membrane. Thus, we reasoned that the introduction of a polar substituent at 7-OH position of 3-O-alkyl di-F-Q would enhance its periplasmic concentration to result in potentiation of ATM at lower concentrations. Results: The title compound 5 exhibited inhibitory activity against NDM-1 as well as the efflux pump of P. aeruginosa, which resulted in synergistical potentiation of ATM. A combination of ATM (8 mg/L) and 5 (8 mg/L) inhibited 80% of the ATM-resistant CPPA, while ATM alone did not show any inhibition. In addition, only 4 mg/L of 5 was needed to reduce the MIC₉₀ of ATM four-fold in ATM-resistant CPPA (n = 15). The time–kill data further supported the effectiveness of the combined treatment of ATM with 5, and the combination of ATM (1xMIC) with 8 mg/L of 5 showed bactericidal effects in every bacterial strain tested (PA-002, bla_IMP, PA-003, bla_VIM, PA-014, bla_GES, and PA-017, bla_NDM) by reducing the bacterial loads by 5.1 log₁₀~8.9 log₁₀. Conclusions: The title compound 5 exhibited inhibitory activity against NDM-1 as well as the efflux pump of P. aeruginosa, and the combined inhibitory activity resulted in synergistical potentiation of ATM. It should be noted that most CPPA isolates tested were sensitized to 8 mg/L of ATM upon combination with 4~8 mg/L of 5. Full article