Humans suffer from various diseases that require more specific drugs to target them. Among the different potent agents, β-lactamases serve as good antibacterial agents; however, β-lactamases are resistant to such antibiotics. The present study was designed to prepare efficient β-lactamase inhibitor amides (12-15) from inexpensive, easily accessible, and bioactive precursors; Morita Baylis Hillman (MBH) adducts (5-8). The adducts (5-8) were primarily prepared by treating their respective aldehydes with the corresponding acrylate in the presence of an organic Lewis base at ambient temperature. The compounds were characterized using mass spectrometry, FTIR and NMR spectroscopy. Furthermore, in silico studies (using AutoDock Tools and AutoDock Vina programs) on the adduct and corresponding amide product revealed that all MBH adducts (5-8) and their product amides (12-15) are significant inhibitors of β-lactamase. Additionally, among the MBH adducts, adduct 7 showed the highest binding affinity with β-lactamase, whereas amide 15 was identified as a highly potent antibacterial based on its docking score (-8.6). In addition, the absorption, distribution, metabolism, and excretion (ADME) test of the synthesized compounds demonstrated that all compounds showed drug-likeness properties.

Peptidoglycan synthesis is an underutilized drug target in Mycobacterium tuberculosis (Mtb). Diazabicyclooctanes (DBOs) are a class of broad-spectrum β-lactamase inhibitors that also inhibit certain peptidoglycan transpeptidases that are important in mycobacterial cell wall synthesis. We evaluated the DBO durlobactam as an inhibitor of BlaC, the Mtb β-lactamase, and multiple Mtb peptidoglycan transpeptidases (PonA1, LdtMt1, LdtMt2, LdtMt3, and LdtMt5). Timed electrospray ionization mass spectrometry (ESI-MS) captured acyl-enzyme complexes with BlaC and all transpeptidases except LdtMt5. Inhibition kinetics demonstrated durlobactam was a potent and efficient DBO inhibitor of BlaC (KI app 9.2 ± 0.9 μM, k2/K 5600 ± 560 M-1 s-1) and similar to clavulanate (KI app 3.3 ± 0.6 μM, k2/K 8400 ± 840 M-1 s-1); however, durlobactam had a lower turnover number (tn = kcat/kinact) than clavulanate (1 and 8, respectively). KI app values with durlobactam and clavulanate were similar for peptidoglycan transpeptidases, but ESI-MS captured durlobactam complexes at more time points. Molecular docking and simulation demonstrated several productive interactions of durlobactam in the active sites of BlaC, PonA1, and LdtMt2. Antibiotic susceptibility testing was conducted on 11 Mtb isolates with amoxicillin, ceftriaxone, meropenem, imipenem, clavulanate, and durlobactam. Durlobactam had a minimum inhibitory concentration (MIC) range of 0.5-16 μg/mL, similar to the ranges for meropenem (1-32 μg/mL) and imipenem (0.5-64 μg/mL). In β-lactam + durlobactam combinations (1:1 mass/volume), MICs were lowered 4- to 64-fold for all isolates except one with meropenem-durlobactam. This work supports further exploration of novel β-lactamase inhibitors that target BlaC and Mtb peptidoglycan transpeptidases.

Mycobacterium abscessus (MAB) infections pose a growing public health threat. Here, we assessed the in vitro activity of the boronic acid-based β-lactamase inhibitor, vaborbactam, with different β-lactams against 100 clinical MAB isolates. Enhanced activity was observed with meropenem and ceftaroline with vaborbactam (1- and >4-fold MIC50/90 reduction). CRISPRi-mediated blaMAB gene knockdown showed a fourfold MIC reduction to ceftaroline but not the other β-lactams. Our findings demonstrate vaborbactam\'s potential in combination therapy against MAB infections.

β-lactam antibiotics are the most successful and commonly used antibacterial agents, but the emergence of resistance to these drugs has become a global health threat. The expression of β-lactamase enzymes produced by pathogens, which hydrolyze the amide bond of the β-lactam ring, is the major mechanism for bacterial resistance to β-lactams. In particular, among class A, B, C and D β-lactamases, metallo-β-lactamases (MBLs, class B β-lactamases) are considered crucial contributors to resistance in gram-negative bacteria. To combat β-lactamase-mediated resistance, great efforts have been made to develop β-lactamase inhibitors that restore the activity of β-lactams. Some β-lactamase inhibitors, such as diazabicyclooctanes (DBOs) and boronic acid derivatives, have also been approved by the FDA. Inhibitors used in the clinic can inactivate mostly serine-β-lactamases (SBLs, class A, C, and D β-lactamases) but have not been effective against MBLs until now. In order to develop new inhibitors particularly for MBLs, various attempts have been suggested. Based on structural and mechanical studies of MBL enzymes, several MBL inhibitor candidates, including taniborbactam in phase 3 and xeruborbactam in phase 1, have been introduced in recent years. However, designing potent inhibitors that are effective against all subclasses of MBLs is still extremely challenging. This review summarizes not only the types of β-lactamase and mechanisms by which β-lactam antibiotics are inactivated, but also the research finding on β-lactamase inhibitors targeting these enzymes. These detailed information on β-lactamases and their inhibitors could give valuable information for novel β-lactamase inhibitors design.

Antimicrobial resistance is a major global health issue. Metallo-β-lactamases (MBL), in particular, are problematic because they can inactivate all classes of β-lactams except aztreonam. Unfortunately, the latter may be simultaneously inactivated by serine β-lactamases. The most dangerous known MBL is New Delhi Metallo-β-lactamase (NDM). This study aimed to test the in vitro susceptibility to aztreonam in combination with novel β-lactamase inhibitors (avibactam, relebactam, and vaborbactam) in clinical strains of Enterobacterales NDM which is resistant to aztreonam. We investigated 21 NDM isolates-including Klebsiella pneumoniae, Escherichia coli, and Citrobacter freundii-which are simultaneously resistant to aztreonam, ceftazidime/avibactam, imipenem/relebactam, and meropenem/vaborbactam. MICs for aztreonam combinations with novel inhibitors were determined using the gradient strip superposition method. The most effective combination was aztreonam/avibactam, active in 80.95% strains, while combinations with relebactam and vaborbactam were effective in 61.90% and 47.62%, respectively. In three studied strains, none of the studied inhibitors restored aztreonam susceptibility. Aztreonam/avibactam has the most significant antimicrobial potential for NDM isolates. However, combinations with other inhibitors should not be rejected in advance because we identified strain susceptible only to tested combinations with inhibitors other than avibactam. Standardization committees should, as soon as possible, develop official methodology for antimicrobial susceptibility testing for aztreonam with β-lactamase inhibitors.

OBJECTIVE: 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 β-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 β-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 β-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 β-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.
CONCLUSIONS: 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.

Metallo-β-lactamases (MBLs) have evolved relatively rapidly to become an international public health threat. There are no clinically available β-lactamase inhibitors with activity against MBLs. This may change with the introduction of cefepime-taniborbactam. Herein, we review three manuscripts (S. I. Drusin, C. Le Terrier, L. Poirel, R. A. Bonomo, et al., Antimicrob Agents Chemother 68:e01168-23, 2024, https://doi.org/10.1128/aac.01168-23; C. Le Terrier, C. Viguier, P. Nordmann, A. J. Vila, and L. Poirel, Antimicrob Agents Chemother 68:e00991-23, 2024, https://doi.org/10.1128/aac.00991-23; D. Ono, M. F. Mojica, C. R. Bethel, Y. Ishii, et al., Antimicrob Agents Chemother 68:e01332-23, 2024, https://doi.org/10.1128/aac.01332-23) in which investigators describe elegant experiments to explore MBL/taniborbactam interactions and modifications to MBLs, in response, to reduce the affinity of taniborbactam. Challenges with MBL inhibition will not disappear; rather, they will evolve commensurate with advancements in medicinal chemistry.

BACKGROUND: Cefiderocol (CFDC) is a novel siderophore-cephalosporin, which usually penetrates the bacteria through the iron-uptake pathways. Data is limited on the factors affecting CFDC activity and methods for overcoming resistance development. Synergistic approaches are needed to tackle antimicrobial resistance. This study aimed to determine CFDC activity on Klebsiella pneumoniae isolates from patients attending a single hospital in the United Arab Emirates (UAE), to explore the effect of β-lactamases on CFDC activity and to enhance CFDC susceptibility in both iron-depleted and iron-enriched conditions.
METHODS: We investigated 238 K. pneumoniae strains from diverse clinical sources. β-lactamase genes were detected by PCR. Susceptibility to CFDC and 12 comparator antibiotics were tested. Combinations of CFDC with β-lactamase inhibitors (BLIs) and/or an outer membrane (OM) permeabilizer (polymyxin B nonapeptide) were tested in iron-depleted and iron-enriched conditions.
RESULTS: CFDC exhibited efficacy of 97.9%, against multidrug-resistant (MDR), and extensively drug-resistant (XDR) strains, in addition to strains resistant to the last resort drugs such as colistin and tigecycline, including dual carbapenemase-producers (blaNDM and blaOXA-48-like) with MIC ≤ 0.06-8 µg/ml. It was effective in killing strains with single and multiple β-lactamases; however, it lost activity in iron-enriched conditions. Synergy was achieved with dual combination of CFDC and BLIs, especially avibactam, which caused a significant reduction in MICs even in iron-enriched conditions. A significant reduction was seen with the triple combination including an OM permeabilizer plus avibactam. Killing-kinetic studies proved that the combination therapy caused dose reduction and faster killing by CFDC than the monotherapy.
CONCLUSIONS: CFDC was deemed effective against MDR and XDR K. pneumoniae. Synergistic combination of CFDC with BLIs and OM permeabilizers could be effective to treat infections in iron-rich sites, but this should be investigated in vivo.

Clinically manifested resistance of bacteria to antibiotics has emerged as a global threat to society and there is an urgent need for the development of novel classes of antibacterial agents. Recently, the use of phosphorus in antibacterial agents has been explored in quite an unprecedent manner. In this comprehensive review, we summarize the use of phosphorus-containing moieties (phosphonates, phosphonamidates, phosphonopeptides, phosphates, phosphoramidates, phosphinates, phosphine oxides, and phosphoniums) in compounds with antibacterial effect, including their use as β-lactamase inhibitors and antibacterial disinfectants. We show that phosphorus-containing moieties can serve as novel pharmacophores, bioisosteres, and prodrugs to modify pharmacodynamic and pharmacokinetic properties. We further discuss the mechanisms of action, biological activities, clinical use and highlight possible future prospects.

BACKGROUND: Despite the availability of new options (ceftazidime-avibactam, imipenem-relebactam, meropenem-vaborbactam and cefiderocol), it is still very difficult to treat infections caused by metallo-β-lactamase (MBLs)-producers resistant to aztreonam. The in vitro efficacy of aztreonam in association with avibactam, vaborbactam or relebactam was evaluated on a collection of MBL-producing Enterobacterales, MBL-producing P. aeruginosa and highly drug-resistant S. maltophilia.
METHODS: A total of fifty-two non-duplicate MBL-producing Enterobacterales, five MBL-producing P. aeruginosa and five multidrug-resistant S. maltophila isolates were used in this study. The minimum inhibitory concentrations (MICs) of aztreonam, meropenem-vaborbactam and imipenem-relebactam were determined by Etest® (bioMérieux, La Balme-les-Grottes) according to EUCAST recommendations. For aztreonam-avibactam, aztreonam-vaborbactam and aztreonam-relebactam associations, the MICs were determined using Etest® on Mueller-Hinton (MH) agar supplemented with 8 mg/L of avibactam, 8 mg/L of vaborbactam and 4 mg/L of relebactam. The MICs were interpreted according to EUCAST guidelines.
RESULTS: The susceptibility rates of aztreonam-avibactam, aztreonam-vaborbactam and aztreonam-relebactam with a standard exposure of aztreonam (1g × 3, IV) were 84.6% (44/52), 55.8% and 34.6% for Enterobacterales and 0% for all combinations for P. aeruginosa and S. maltophila. The susceptibility rates of aztreonam-avibactam, aztreonam-vaborbactam and aztreonam-relebactam with a high exposure of aztreonam (2g × 4, IV) were 92.3%, 78.9% and 57.7% for Enterobacterales, 75%, 60% and 60% for P. aeruginosa and 100%, 100% and 40% for S. maltophila.
CONCLUSIONS: As previously demonstrated for an aztreonam/ceftazidime-avibactam combination, aztreonam plus imipenem-relebactam and aztreonam plus meropenem-vaborbactam might be useful options, but with potentially lower efficiency, to treat infections caused by aztreonam-non-susceptible MBL-producing Gram-negative strains.