Reprogramming of antibiotics to combat antimicrobial resistance

Repurposing fusidic acid as an antimicrobial against enterococci with a low probability of resistance development

Drug repurposing constitutes a strategy to combat antimicrobial resistance, by using agents with known safety, pharmacokinetics, and pharmacodynamics. Previous studies have implemented new fusidic acid (FA) front-loading-dose regimens, allowing higher serum levels than those achievable with ordinary doses. As susceptibility breakpoints are affected by serum level, we evaluated the repurposing of FA as an antimicrobial product against enterococci. FA minimum inhibitory concentrations (MICs) against standard enterococci strains; Enterococcus faecalis ATCC 29212 and Enterococcus faecium ATCC 27270 were 2 and 4 µg/mL, respectively. The MIC against 98 enterococcal clinical isolates was ≤ 8 µg/mL; all would be susceptible if categorized according to recalculated breakpoints (≥ 16 µg/mL), based on the serum level achieved using the front-loading regimen. FA administration in vivo, using the BALB/c mouse infection model, significantly reduced bacterial burden by two to three log10 units in the liver and spleen of mice infected with vancomycin-susceptible and -resistant strains. Exposure of the standard enterococcal strains to increasing, but not fixed, FA concentrations resulted in resistant strains (MIC = 128 µg/mL), with thicker cell walls and slower growth rates. Only one mutation (M651I) was detected in the fusA gene of the resistant strain derived from serial passage of E. faecium ATCC 27270, which was retained in the revertant strain after passage in the FA-free medium. In conclusion, FA can be repurposed as an antimicrobial drug against enterococci with a low probability of mutational resistance development, and can be employed for treatment of infections attributable to vancomycin-resistant enterococci.

Synthesis and biological evaluation of novel benzenesulfonamide incorporated thiazole-triazole hybrids as antimicrobial and antioxidant agents

A library of 20 novel benzenesulfonamide incorporating thiazole tethered 1,2,3-triazoles 1-4a-e was synthesized and screened for their antimicrobial, antioxidant, and cytotoxicity studies. Amoxicillin and fluconazole were used as reference antibacterial and antifungal drugs, respectively. Further, energies of frontier molecular orbitals were calculated for all the synthesized target compounds 1-4a-e to correlate electronic parameters with the observed biological results. Global reactivity descriptors, including highest occupied molecular orbitals-lowest unoccupied molecular orbitals energy gap, electronegativity, chemical hardness, chemical softness, and electrophilicity index, were also calculated for the synthesized molecules. All the tested compounds possessed moderate to excellent antibacterial potency; however, 3d and 4d exhibited the overall highest antibacterial effect (minimum inhibitory concentration [MIC] values 5-11 µM) while 2c showed the highest antifungal effect (MIC value 6 µM). Compound 3c exhibited the highest antioxidant activity with a % radical scavenging activity value of 95.12. The cytotoxicity of the compounds 1-4a-e was also checked against an animal cell line and a plant seed germination cell line, and the compounds were found to be safe against both the tested cell lines.

Alkyl gallates inhibit serine O-acetyltransferase in bacteria and enhance susceptibility of drug-resistant Gram-negative bacteria to antibiotics

A principal concept in developing antibacterial agents with selective toxicity is blocking metabolic pathways that are critical for bacterial growth but that mammalian cells lack. Serine O-acetyltransferase (CysE) is an enzyme in many bacteria that catalyzes the first step in l-cysteine biosynthesis by transferring an acetyl group from acetyl coenzyme A (acetyl-CoA) to l-serine to form O-acetylserine. Because mammalian cells lack this l-cysteine biosynthesis pathway, developing an inhibitor of CysE has been thought to be a way to establish a new class of antibacterial agents. Here, we demonstrated that alkyl gallates such as octyl gallate (OGA) could act as potent CysE inhibitors in vitro and in bacteria. Mass spectrometry analyses indicated that OGA treatment markedly reduced intrabacterial levels of l-cysteine and its metabolites including glutathione and glutathione persulfide in Escherichia coli to a level similar to that found in E. coli lacking the cysE gene. Consistent with the reduction of those antioxidant molecules in bacteria, E. coli became vulnerable to hydrogen peroxide-mediated bacterial killing in the presence of OGA. More important, OGA treatment intensified susceptibilities of metallo-β-lactamase-expressing Gram-negative bacteria (E. coli and Klebsiella pneumoniae) to carbapenem. Structural analyses showed that alkyl gallate bound to the binding site for acetyl-CoA that limits access of acetyl-CoA to the active site. Our data thus suggest that CysE inhibitors may be used to treat infectious diseases caused by drug-resistant Gram-negative bacteria not only via direct antibacterial activity but also by enhancing therapeutic potentials of existing antibiotics.

Photocatalytic degradation of four emerging antibiotic contaminants and toxicity assessment in wastewater: A comprehensive study

Excessive usage and unrestricted discharge of antibiotics in the environment lead to their accumulation in the ecosystem due to their highly stable and non-biodegradation nature. Photodegradation of four most consumed antibiotics such as amoxicillin, azithromycin, cefixime, and ciprofloxacin were studied using Cu2O-TiO2 nanotubes. Cytotoxicity evaluation of the native and transformed products was conducted on the RAW 264.7 cell lines. Photocatalyst loading (0.1-2.0 g/L), pH (5, 7 and 9), initial antibiotic load (50-1000 μg/mL) and cuprous oxide percentage (5, 10 and 20) were optimized for efficient photodegradation of antibiotics. Quenching experiments to evaluate the mechanism of photodegradation with hydroxyl and superoxide radicals were found the most reactive species of the selected antibiotics. Complete degradation of selected antibiotics was achieved in 90 min with 1.5 g/L of 10% Cu2O-TiO2 nanotubes with initial antibiotic concentration (100 μg/mL) at neutral pH of water matrix. The photocatalyst showed high chemical stability and reusability up to five consecutive cycles. Zeta potential studies confirms the high stability and activity of 10% C-TAC (Cuprous oxide doped Titanium dioxide nanotubes for Applied Catalysis) in the tested pH conditions. Photoluminescence and Electrochemical Impedance Spectroscopy data speculates that 10% C-TAC photocatalyst have efficient photoexcitation in the visible light for photodegradation of antibiotics samples. Inhibitory concentration (IC50) interpretation from the toxicity analysis of native antibiotics concluded that ciprofloxacin was the most toxic antibiotic among the selected antibiotics. Cytotoxicity percentage of transformed products showed r: -0.985, p: 0.01 (negative correlation) with the degradation percentage revealing the efficient degradation of selected antibiotics with no toxic by-products.

Decentralized systems for the treatment of antimicrobial compounds released from hospital aquatic wastes

In many developing countries, untreated hospital effluents are discharged and treated simultaneously with municipal wastewater. However, if the hospital effluents are not treated separately, they pose concerning health risks due to the possible transport of the antimicrobial genes and microbes in the environment. Such effluent is considered as a point source for a number of potentially infectious microorganisms, waste antimicrobial compounds and other contaminants that could promote antimicrobial resistance development. The removal of these contaminants prior to discharge reduces the exposure of antimicrobials to the environment and this should lower the risk of superbug development. At an effluent discharge site, suitable pre-treatment of wastewater containing antimicrobials could maximise the ecological impact with potentially reduced risk to human health. In addressing these points, this paper reviews the applications of decentralized treatment systems toward reducing the concentration of antimicrobials in wastewater. The most commonly used techniques in decentralized wastewater treatment systems for onsite removal of antimicrobials were discussed and evidence suggests that hybrid techniques should be more useful for the efficient removal of antimicrobials. It is concluded that alongside the cooperation of administration departments, health industries, water treatment authorities and general public, decentralized treatment technology can efficiently enhance the removal of antimicrobial compounds, thereby decreasing the concentration of contaminants released to the environment that could pose risks to human and ecological health due to development of antimicrobial resistance in microbes.

New Quinazolin-4(3H)-one Derivatives Incorporating Hydrazone and Pyrazole Scaffolds as Antimicrobial Agents Targeting DNA Gyraze Enzyme

The present work includes the synthesis of a new series of quinazolin-4(3H)-one compounds (4a–f, 5a–d) as antimicrobial agents. The starting compound, 2-hydrazinylquinazolin-4(3H)-one (2), was synthesized and treated with different carbonyl compounds to afford the hydrazone derivatives 4a–f. In addition, the hydrazone derivatives 4a–d were treated with a DMF/POCl3 mixture to give the formyl-pyrazole derivatives 5a–d. All the target compounds were evaluated as antimicrobial agents against four bacterial and four fungal strains. The majority of the tested compounds showed potent antimicrobial activity compared with the reference antibiotics. The most potent antimicrobial activity was shown by 5a with MIC values in the range (1–16) μg/mL. In addition, the most potent compounds against E. coli were evaluated for their inhibitory activity against E. coli DNA gyrase, whereas the target compounds 4a, 5a, 5c, and 5d showed the most potent inhibition to the target enzyme with IC50 values ranging from 3.19 to 4.17 µM. Furthermore, molecular docking studies were performed for the most active compounds against the target E. coli DNA gyrase to determine their binding affinity within the enzyme’s active site. Moreover, ADME evaluations of these compounds predicted their high oral bioavailability and good GI absorption.

Dual Acting Immuno-Antibiotics: Computational Investigation on Antibacterial Efficacy of Immune Boosters Against Isoprenoid H Enzyme

Drug-resistant infections have become a serious threat to human health in the past two decades. Global Antimicrobial Surveillance (GLASS) in January 2018 reported widespread antibiotic resistance among 1.5 million people infected with bacteria across 22 countries. According to prominent economist Jim O'Neil, antimicrobial resistance is estimated to kill ∼10 million people affected by microorganisms each year by 2050. Even though multiple therapeutics are now available to treat the infections, more and more bacterial strains have acquired resistance to these treatments through various techniques. Moreover, the decrease in the pipeline of antibacterial medicines under clinical development has become a significant problem. In this scenario, the development of novel antibiotics that act on untapped pathways is necessary to combat the bacterial infections. Isoprenoid H (IspH) synthetase has become an attractive antibacterial target as there is no human homologue. IspH is an enzyme involved in methyl-d-erythritol phosphate (MEP) pathway of isoprenoid synthesis and is conserved in gram-negative bacteria, mycobacteria, and apicomplexans. Since, IspH is a novel therapeutic target, explorations are only just beginning, and despite the progress made in this area, no single IspH inhibitor is available in the market for therapeutic use. In this article, we have repurposed 35 immune boosters against IspH enzyme using methods such as extra-precision docking and Molecular Mechanics Generalized Born Surface Area (MMGBSA). Among them, 4'-fluorouridine was found to be active because of its glide score and significant binding affinity with IspH enzyme. Furthermore, this study requires more in vitro, in vivo, and molecular dynamics studies to support our findings.

Cysteine Hydropersulfide Inactivates β-Lactam Antibiotics with Formation of Ring-Opened Carbothioic S-Acids in Bacteria

Hydrogen sulfide (H₂S) formed during sulfur metabolism in bacteria has been implicated in the development of intrinsic resistance to antibacterial agents. Despite the conversion of H₂S to hydropersulfides greatly enhancing the biochemical properties of H₂S such as antioxidant activity, the effects of hydropersulfides on antibiotic resistance have remained unknown. In this work, we investigated the effects of H₂S alone or together with cystine to form cysteine hydropersulfide (CysSSH) on the activities of antibacterial agents. By using the disc diffusion test, we found that CysSSH treatment effectively inactivated β-lactams of the penicillin class (penicillin G and ampicillin) and the carbapenem class (meropenem). These β-lactams were resistant to treatment with H₂S alone or cystine alone. In contrast, cephalosporin class β-lactams (cefaclor and cefoperazone) and non-β-lactam antibiotics (tetracycline, kanamycin, erythromycin, and ofloxacin) were stable after CysSSH treatment. Chromatographic and mass spectrometric analyses revealed that CysSSH directly reacted with β-lactams to form β-lactam ring-opened carbothioic S-acids (BL-COSH). Furthermore, we demonstrated that certain bacteria (e.g., Escherichia coli and Staphylococcus aureus) efficiently decomposed β-lactam antibiotics to form BL-COSH, which were transported to the extracellular space. These data suggest that CysSSH-mediated β-lactam decomposition may contribute to intrinsic bacterial resistance to β-lactams. BL-COSH may become useful biomarkers for CysSSH-mediated β-lactam resistance and for investigation of potential antibacterial adjuvants that can enhance the antibacterial activity of β-lactams by reducing the hydropersulfides in bacteria.