The intriguing biology and chemistry of fosfomycin: the only marketed phosphonate antibiotic

Oxydifficidin, a potent Neisseria gonorrhoeae antibiotic due to DedA-assisted uptake and ribosomal protein RplL sensitivity

Gonorrhea, which is caused by Neisseria gonorrhoeae, is the second most reported sexually transmitted infection worldwide. The increasing appearance of isolates that are resistant to approved therapeutics raises the concern that gonorrhea may become untreatable. Here, we serendipitously identified oxydifficidin as a potent N. gonorrhoeae antibiotic through the observation of a Bacillus amyloliquefaciens contaminant in a lawn of N. gonorrhoeae. Oxydifficidin is active against both wild-type and multidrug-resistant N. gonorrhoeae. Its potent activity results from a combination of DedA-assisted uptake into the cytoplasm and the presence of an oxydifficidin-sensitive ribosomal protein L7/L12 (RplL). Our data indicate that oxydifficidin binds to the ribosome at a site that is distinct from other antibiotics and that L7/L12 is uniquely associated with its mode of action. This study opens a potential new avenue for addressing antibiotic resistant gonorrhea and underscores the possibility of identifying overlooked natural products from cultured bacteria, particularly those with activity against previously understudied pathogens.

Treatment of Complicated Gram-Positive Bacteremia and Infective Endocarditis

The Gram-positive cocci Staphylococcus aureus, Streptococcus spp., and Enterococcus spp. are the most frequent causative organisms of bloodstream infections and infective endocarditis. "Complicated bacteremia" is a term used in S. aureus bloodstream infections and originally implied the presence of metastatic infectious foci (i.e. complications of S. aureus bacteremia). These complications demand longer antimicrobial treatment durations and, frequently, interventional source control. Several risk factors for the incidence of bacteremia complications have been identified and are often used for the definition of complicated bacteremia. Here, we discuss management and diagnostic approaches and treatment options for patients with complicated bacteremia, with particular focus on infective endocarditis. We also summarize the available evidence regarding imaging modalities and the choice of antimicrobial mono- or combination therapy according to resistance patterns for these pathogens as well as treatment durations and optimized application routes. Finally, we synopsize current and future areas of research in complicated bacteremia and infective endocarditis.

Determinants of Antibiotic Resistance and Virulence Factors in the Genome of Escherichia coli APEC 36 Strain Isolated from a Broiler Chicken with Generalized Colibacillosis

Objective: Multidrug-resistant, highly pathogenic Escherichia coli strains are the primary causative agents of intestinal and extraintestinal human diseases. The extensive utilization of antibiotics for farm animals has been identified as a contributing factor to the emergence and dissemination of E. coli strains that exhibit multidrug resistance and possess high pathogenic potential. Consequently, a significant research objective is to examine the genetic diversity of pathogenic E. coli strains and to identify those that may pose a threat to human health. Methods: In this study, we present the results of genome sequencing and analysis, as well as the physiological characterization of E. coli strain APEC 36, which was isolated from the liver of a broiler chicken with generalized colibacillosis. Results: We found that APEC 36 possess a number of mechanisms of antibiotic resistance, including antibiotic efflux, antibiotic inactivation, and antibiotic target alteration/replacement/protection. The most widely represented group among these mechanisms was that of antibiotic efflux. This finding is consistent with the strain's documented resistance to multiple antibiotics. APEC 36 has an extremely rare variant of the beta-lactamase CTX-M-169. Notwithstanding the multitude of systems for interfering with foreign DNA present in the strain, seven plasmids have been identified, three of which may possess novel replication origins. Additionally, qnrS1, which confers resistance to fluoroquinolones, was found to be encoded in the genome rather than in the plasmid. This suggests that the determinants of antibiotic resistance may be captured in the genome and stably transmitted from generation to generation. Conclusions: The APEC 36 strain has genes for toxins, adhesins, protectins, and an iron uptake system. The obtained set of genetic and physiological characteristics allowed us to assume that this strain has a high pathogenic potential for humans.

Effect of fosfomycin-induced hypernatremia on patients' hospital stay length and survival

BACKGROUND AND OBJECTIVE

Hypernatremia is a possible side effect of intravenous fosfomycin. The aim of this study was to investigate the effects of changes in sodium (Na) levels on hospital stay and survival in patients hospitalized in the intensive care unit receiving fosfomycin.

SUBJECTS AND METHODS

This study was conducted retrospectively on the files of patients over the age of 60, who were admitted to the Internal Medicine Intensive Care Unit. Plasma sodium levels were observed and documented over a period of 14 days. The patients were divided into two groups (Hypernatremia group Na > 145 mEq/L vs normonatremia group 135-145 mEq/L). In addition, daily sodium changes were noted for 14 days in patients.

RESULTS

The mean age of the patients was 75 years. Hospitalization days were longer for hypernatremia patients (31.5 days vs 41 days, p = 0.003). Patients with hypernatremia had an extended duration of stay in the intensive care unit. (21 days vs 31 days p = 0.002). The 1-month survival rate was 61.4% in patients with hypernatremia and 24.9% in patients without hypernatremia (p = 0.004). The absence of hypernatremia increases mortality by 2.09 times (95% CI 1.35-3.23). When discharge and mortality rates were analyzed according to sodium fluctuation, discharged patients exhibited a lower sodium fluctuation (4 min/max (-10/19) vs 6 min/max (-16/32) p < 0.001).

CONCLUSION

In conclusion, the strength of our study is that it specifically focuses on the consequences of the sodium fluctuation on patient management and provides results.

Oxydifficidin, a potent Neisseria gonorrhoeae antibiotic due to DedA assisted uptake and ribosomal protein RplL sensitivity

Gonorrhea, which is caused by Neisseria gonorrhoeae, is the second most reported sexually transmitted infection worldwide. The increasing appearance of isolates that are resistant to approved therapeutics raises the concern that gonorrhea may become untreatable. Here, we serendipitously identified oxydifficidin as a potent N. gonorrhoeae antibiotic through the observation of a Bacillus amyloliquefaciens contaminant in a lawn of N. gonorrhoeae. Oxydifficidin is active against both wild-type and multidrug-resistant N. gonorrhoeae. It's potent activity results from a combination of DedA-assisted uptake into the cytoplasm and the presence of an oxydifficidin-sensitive ribosomal protein L7/L12 (RplL). Our data indicates that oxydifficidin binds to the ribosome at a site that is distinct from other antibiotics and that L7/L12 is uniquely associated with its mode of action. This study opens a potential new avenue for addressing antibiotic resistant gonorrhea and underscores the possibility of identifying overlooked natural products from cultured bacteria, particularly those with activity against previously understudied pathogens.

Role of Carbon, Nitrogen, Phosphate and Sulfur Metabolism in Secondary Metabolism Precursor Supply in Streptomyces spp

The natural soil environment of Streptomyces is characterized by variations in the availability of nitrogen, carbon, phosphate and sulfur, leading to complex primary and secondary metabolisms. Their remarkable ability to adapt to fluctuating nutrient conditions is possible through the utilization of a large amount of substrates by diverse intracellular and extracellular enzymes. Thus, Streptomyces fulfill an important ecological role in soil environments, metabolizing the remains of other organisms. In order to survive under changing conditions in their natural habitats, they have the possibility to fall back on specialized enzymes to utilize diverse nutrients and supply compounds from primary metabolism as precursors for secondary metabolite production. We aimed to summarize the knowledge on the C-, N-, P- and S-metabolisms in the genus Streptomyces as a source of building blocks for the production of antibiotics and other relevant compounds.

A review of organophosphonates, their natural and anthropogenic sources, environmental fate and impact on microbial greenhouse gases emissions - Identifying knowledge gaps

Organophosphonates (OPs) are a unique group of natural and synthetic compounds, characterised by the presence of a stable, hard-to-cleave bond between the carbon and phosphorus atoms. OPs exhibit high resistance to abiotic degradation, excellent chelating properties and high biological activity. Despite the huge and increasing scale of OP production and use worldwide, little is known about their transportation and fate in the environment. Available data are dominated by information concerning the most recognised organophosphonate - the herbicide glyphosate - while other OPs have received little attention. In this paper, a comprehensive review of the current state of knowledge about natural and artificial OPs is presented (including glyphosate). Based on the available literature, a number of knowledge gaps have been identified that need to be filled in order to understand the environmental effects of these abundant compounds. Special attention has been given to GHG-related processes, with a particular focus on CH4. This stems from the recent discovery of OP-dependent CH4 production in aqueous environments under aerobic conditions. The process has changed the perception of the biogeochemical cycle of CH4, since it was previously thought that biological methane formation was only possible under anaerobic conditions. However, there is a lack of knowledge on whether OP-associated methane is also formed in soils. Moreover, it remains unclear whether anthropogenic OPs affect the CH4 cycle, a concern of significant importance in the context of the increasing rate of global warming. The literature examined in this review also calls for additional research into the date of OPs in waste and sewage and in their impact on environmental microbiomes.

Harvesting phosphorus-containing moieties for their antibacterial effects

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.

Visible light-enabled synthesis of phosphorylated indolizine and pyridoindole derivatives via HAT-mediated radical cascade cyclization

A visible light-enabled cascade cyclization strategy is disclosed with concomitant phosphorylation and heterocycle construction. It provides a novel and environmentally benign approach for accessing tetrahydroindolizine-containing phosphonates under metal-free conditions. Mechanistic studies revealed that phosphinoyl radicals were generated from H-phosphonates via a HAT process.

Stability Study of Fosfomycin in Elastomeric Pumps at 4 °C and 34 °C: Technical Bases for a Continuous Infusion Use for Outpatient Parenteral Antibiotic Therapy

BACKGROUND

Fosfomycin acts against aerobic Gram-/+ bacteria by blocking the synthesis of peptidoglycan. Its use has been currently re-evaluated for intravenous administration for the treatment of systemic infections by multidrug-resistant bacteria. Concentration-/time-dependent activity has been suggested, with potential clinical advantages from prolonged or continuous infusion. Nevertheless, little is known about Fosfomycin stability in elastomeric pumps. The aim of the present work was stability investigation before administration at 4 °C and during administration at 34 °C.

METHODS

InfectoFos® (InfectoPharm s.r.l., Milan, Italy) preparation for intravenous use in elastomeric pumps at 4 °C and 34 °C was analyzed following EMA guidelines for drug stability. Samples were analyzed with an ultra-high performance liquid chromatography coupled with tandem mass spectrometry method on a LX50® UHPLC system equipped with a QSight 220® (Perkin Elmer, Milan, Italy) tandem mass spectrometer.

RESULTS

Fosfomycin in elastomeric preparation is stable for at least 5 days at a storage temperature of 4 °C and 34 °C.

CONCLUSIONS

The results suggest Fosfomycin eligibility for continuous infusion even in the context of outpatient parenteral antibiotic therapy. Therefore, this approach should be tested in clinical and pharmacokinetic studies, in order to evaluate the possible gains in the pharmacokinetic profile and the clinical effectiveness.

Reliability of E-Tests and the Phoenix Automated Method in Assessing Susceptibility to IV Fosfomycin-Comparative Studies Relative to the Reference Method

The agar dilution method (ADM) recommended for IV fosfomycin (IV FOS) is complex and labor-intensive. Keeping in mind the reality of everyday laboratory work, we have evaluated the agreement of IV FOS susceptibility results obtained using the E-test and the Phoenix system with the results obtained using the ADM.

MATERIALS AND METHODS

The tests were performed on 860 strains. To evaluate susceptibility to IV FOS, BioMerieux E-tests (bioMerieux, Warsaw, Poland), BD Phoenix panels (BD Phoenix, Sparks, MD, USA), and the ADM were used. Clinical interpretation was performed in accordance with EUCAST Guidance (v12.0, 2021). The significance of the E-test and the Phoenix was analyzed in relation to the ADM by defining categorical agreement (CA), major error (ME), and very major error (VME). Essential agreement (EA) has also been defined for the E-test. A method was considered reliable, in accordance with ISO 20776-2:2007, when CA and EA were above 89.9% and VME was <3%.

RESULTS

A categorical agreement of >98.9% was demonstrated between the E-test and the ADM for overall strains and for Echerichia coli, ESBL-producing Enterobacterales, and Staphylococcus aureus, while between the Phoenix and the ADM, a CA of >98.9% was shown only for Escherichia coli, Staphylococcus aureus, and Proteus spp. A very major error rate of <3% was obtained only for Staphylococcus aureus and MBL-producing Pseudomonas evaluated by both the E-test and the Phoenix. An essential agreement of >98.9% between the E-test and the ADM has not been demonstrated for any of the tested groups of strains. The Phoenix yielded more VMEs than the E-test (50 and 46, respectively). The highest VME rate was demonstrated using the Phoenix method for Enterobacter spp. (53.83%).

CONCLUSIONS

Both the E-test and the Phoenix have turned out to be reliable in assessing IV FOS susceptibility only for Staphylococcus aureus (CA > 89.9% and VME < 3%). For the remaining tested groups of strains and genera, the simultaneous high CA rate and low VME rate required by ISO were not achieved. Both methods fared particularly badly in detecting strains resistant to IV.

Advances in the Synthesis and Analysis of Biologically Active Phosphometabolites

Phosphorus-containing metabolites cover a large molecular diversity and represent an important domain of small molecules which are highly relevant for life and represent essential interfaces between biology and chemistry, between the biological and abiotic world. The large but not unlimited amount of phosphate minerals on our planet is a key resource for living organisms on our planet, while the accumulation of phosphorus-containing waste is associated with negative effects on ecosystems. Therefore, resource-efficient and circular processes receive increasing attention from different perspectives, from local and regional levels to national and global levels. The molecular and sustainability aspects of a global phosphorus cycle have become of much interest for addressing the phosphorus biochemical flow as a high-risk planetary boundary. Knowledge of balancing the natural phosphorus cycle and the further elucidation of metabolic pathways involving phosphorus is crucial. This requires not only the development of effective new methods for practical discovery, identification, and high-information content analysis, but also for practical synthesis of phosphorus-containing metabolites, for example as standards, as substrates or products of enzymatic reactions, or for discovering novel biological functions. The purpose of this article is to review the advances which have been achieved in the synthesis and analysis of phosphorus-containing metabolites which are biologically active.

Assessment of the Susceptibility of Clinical Gram-Negative and Gram-Positive Bacterial Strains to Fosfomycin and Significance of This Antibiotic in Infection Treatment

Multidrug resistance of bacteria has prompted intensive development work on new medicines, but also the search for effective options among the oldest antibiotics. Although intravenous fosfomycin (IVFOS) seems to be an interesting proposal, the recommended agar dilution method for susceptibility determination poses a major problem in routine diagnostic testing. As a consequence, there is a lack of comprehensive data on the frequency of isolation of susceptible or resistant strains. This fact triggered the disposition of EUCAST concerning the revision of IVFOS breakpoints (BPs), including withdrawal of BPs for Enterobacterales (excluding E. coli) and coagulase-negative staphylococci. Therefore, the aim of this study was to assess the activity of fosfomycin against numerous clinical strains using recommended methods. Materials and methods: A total of 997 bacterial strains were tested from the following genera: Enterobacterales, Pseudomonas spp., Staphylococcus spp., Acinetobacter spp., and Enterococcus spp., for which there are currently no BPs. The strains were isolated from various clinical materials from patients hospitalized in five hospitals. During the investigation, the recommended agar dilution method was used. Susceptibility to other antibiotics and resistance mechanisms were determined using an automatic method (Phoenix) the disk diffusion method, and E-tests. MIC values of fosfomycin were estimated for all strains and for susceptible and multidrug-resistant (MDR) strains individually. Results: Except for Acinetobacter and Enterococcus, 83% of the strains were susceptible to IVFOS, including the largest percentage of S. aureus and E. coli. Klebsiella spp. turned out to be the least susceptible strains (66%). The highest proportion of susceptibility to fosfomycin was found among strains that were sensitive to other antibiotics (80.9%), and the lowest was found among Gram-negative carbapenemase-producing bacteria (55.6%) and ESBL+ bacteria (61.6%). The MIC evaluation revealed the lowest MIC₅₀ and MIC₉₀ values for S. aureus (0.5 mg/L and 1 mg/L, respectively) and E. coli (4 mg/L and 32 mg/L, respectively). The highest values of MIC₅₀ were found for Acinetobacter spp. (256 mg/L), while the highest values of MIC₉₀ were found for Acinetobacter spp. and Klebsiella spp. (256 mg/L and 512 mg/L, respectively). Conclusions: IVFOS appears to be suitable for the treatment of many infections, including the empirical treatment of polymicrobial infections and those caused by MDR strains, since the sensitivity of the studied strains to this antibiotic in different groups ranged from 66% to as much as 99%. Sensitivity to fosfomycin was also demonstrated by 60% of carbapenem-resistant strains; therefore, IVFOS is one of the few therapeutic options that can be effective against the most resistant Gram-negative rods. In light of the general consultation posted by EUCAST, obtaining data such as IVFOS MIC value distributions may be vital for the decision of implementing fosfomycin into breakpoint tables.

Serendipitous Discovery of a Competitive Inhibitor of FraB, a Salmonella Deglycase and Drug Target

Although salmonellosis, an infectious disease, is a significant global healthcare burden, there are no Salmonella-specific vaccines or therapeutics for humans. Motivated by our finding that FraB, a Salmonella deglycase responsible for fructose-asparagine catabolism, is a viable drug target, we initiated experimental and computational efforts to identify inhibitors of FraB. To this end, our recent high-throughput screening initiative yielded almost exclusively uncompetitive inhibitors of FraB. In parallel with this advance, we report here how a separate structural and computational biology investigation of FrlB, a FraB paralog, led to the serendipitous discovery that 2-deoxy-6-phosphogluconate is a competitive inhibitor of FraB (KI ~ 3 μM). However, this compound was ineffective in inhibiting the growth of Salmonella in a liquid culture. In addition to poor uptake, cellular metabolic transformations by a Salmonella dehydrogenase and different phosphatases likely undermined the efficacy of 2-deoxy-6-phosphogluconate in live-cell assays. These insights inform our ongoing efforts to synthesize non-hydrolyzable/-metabolizable analogs of 2-deoxy-6-phosphogluconate. We showcase our findings largely to (re)emphasize the role of serendipity and the importance of multi-pronged approaches in drug discovery.

Covalent inhibitors of bacterial peptidoglycan biosynthesis enzyme MurA with chloroacetamide warhead

MurA (UDP-N-acetylglucosamine enolpyruvyl transferase) catalyzes the first committed step in the cytoplasmic part of peptidoglycan biosynthesis and is a validated target enzyme for antibacterial drug discovery; the inhibitor fosfomycin has been used clinically for decades. Like fosfomycin, most MurA inhibitors are small heterocyclic compounds that inhibit the enzyme by forming a covalent bond with the active site cysteine. The reactive chloroacetamide group was selected from a series of suitable electrophilic thiol-reactive warheads. The predominantly one-step synthesis led to the construction of the final library of 47 fragment-sized chloroacetamide compounds. Several new E. coli MurA inhibitors were identified, with the most potent compound having an IC₅₀ value in the low micromolar range. The electrophilic reactivity of all chloroacetamide fragments in our library was evaluated by a high-throughput spectrophotometric assay using the reduced Ellman reagent as a surrogate for the cysteine thiol. LC-MS/MS experiments confirmed the covalent binding of the most potent inhibitor to Cys115 of the digested MurA enzyme. The covalent binding was further investigated by a biochemical time-dependent assay and a dilution assay, which confirmed the irreversible and time-dependent mode of action. The efficacy of chloroacetamide derivatives against MurA does not correlate with their thiol reactivity, making the active fragments valuable starting points for fragment-based development of new antibacterial agents targeting MurA.

In(OTf)3-catalyzed N-α phosphonylation of N,O-acetals with triethyl phosphite

A practical approach to α-aminophosphonates has been developed through an In(OTf)₃-catalyzed N-α phosphonylation of N,O-acetals with triethyl phosphite 7. Indoline and isoindoline N,O-acetals 6a-6j and 9a-9j and chain N,O-acetals 11a-11p were subjected to a Lewis acid catalyzed N-α phosphonylation process. As a result, the desired α-aminophosphonates 8a-8j, 10a-10j and 12a-12p were obtained in moderate to good yields.

Harnessing phosphonate antibiotics argolaphos biosynthesis enables a synthetic biology-based green synthesis of glyphosate

Glyphosate is a widely used herbicide with an annual production of more than one million tons globally. Current commercialized production processes of glyphosate are generally associated with manufacturing hazards and toxic wastes. Recently, many countries have strengthened environmental supervision and law enforcement on glyphosate manufacturing. Therefore, a green source of glyphosate is required. Here, we characterize the genes required for producing aminomethylphosphonate (AMP), one of the intermediates in the biosynthesis of the potent antibiotics argolaphos. We apply a synthetic biology strategy to improve AMP production in Streptomyces lividans, with fermentation titers of 52 mg L-1, a 500-fold improvement over the original strain. Furthermore, we develop an efficient and practical chemical process for converting AMP to glyphosate. Our findings highlight one greenness-driven alternative in the production of glyphosate.

The Impact of the Antibiotic Fosfomycin on Wastewater Communities Measured by Flow Cytometry

Fosfomycin is a re-emergent antibiotic known to be effective against severe bacterial infections even when other antibiotics fail. To avoid overuse and thus the risk of new antibiotic resistance, the European Commission has recommended the intravenous use of fosfomycin only when other antibiotic treatments fail. A release of fosfomycin into the environment via wastewater from not only municipalities but also already from the producing pharmaceutical industry can seriously undermine a sustaining therapeutic value. We showed in long-term continuous-mode bioreactor cultivation and by using microbial community flow cytometry, microbial community ecology tools, and cell sorting that the micro-pollutant altered the bacterial wastewater community (WWC) composition within only a few generations. Under these conditions, fosfomycin was not readily degraded both at lower and higher concentrations. At the same time, operational reactor parameters and typical diversity parameters such as α- and intracommunity β-diversity did not point to system changes. Nevertheless, an intrinsic compositional change occurred, caused by a turnover process in which higher concentrations of fosfomycin selected for organisms known to frequently harbor antibiotic resistance genes. A gfp-labeled Pseudomonas putida strain, used as the model organism and a possible future chassis for fosfomycin degradation pathways, was augmented and outcompeted in all tested situations. The results suggest that WWCs, as complex communities, may tolerate fosfomycin for a time, but selection for cell types that may develop resistance is very likely. The approach presented allows very rapid assessment and visualization of the impact of antibiotics on natural or managed microbial communities in general and on individual members of these communities in particular.

Inhibition of MurA Enzyme from Escherichia coli and Staphylococcus aureus by Diterpenes from Lepechinia meyenii and Their Synthetic Analogs

Enzymes MurA and MurF, involved in bacterial cell wall synthesis, have been validated as targets for the discovery of novel antibiotics. A panel of plant-origin antibacterial diterpenes and synthetic analogs derived therefrom were investigated for their inhibitory properties on these enzymes from Escherichia coli and Staphylococcus aureus. Six compounds were proven to be effective for inhibiting MurA from both bacteria, with IC50 values ranging from 1.1 to 25.1 µM. To further mechanistically investigate the nature of binding and to explain the activity, these compounds were docked into the active site of MurA from E. coli. The aromatic ring of the active compounds showed a T-shaped π-π interaction with the phenyl ring of Phe328, and at least one hydrogen bond was formed between the hydroxy groups and Arg120 and/or Arg91. The results disclosed here establish new chemical scaffolds for the development of novel entities targeting MurA as potential antibiotics to combat the threat of pathogenic bacteria, particularly resistant strains.

Phosphonates as Unique Components of Plant Seeds-A Promising Approach to Use Phosphorus Profiles in Plant Chemotaxonomy

Phosphorus is one of the most important elements essential for all living beings. Plants accumulate and store phosphorous in various forms that have diverse physiological and biochemical functions. In this study, we determine and then examine the phosphorus profiles of seeds of plants belonging to different taxa based on extractable inorganic phosphates and organic forms of phosphorus. We paid particular attention to the presence of natural phosphonates in the tested materials. The inorganic phosphates were determined colorimetrically, whereas phosphorus profiles were created by using 31P NMR spectroscopy. Our study on phosphorus profiles revealed that the obtainedsets of data vary significantly among the representatives of different taxa and were somehow specific for families of plants. It should be emphasised that the measurements obtained using 31P NMR spectroscopy undoubtedly confirmed-for the first time-the presence of phosphonates among the natural components of plant seeds. Hence, the classification of plants considering the phosphorus profiles, including the presence of phosphonates, may be a new additional chemotaxonomic feature.

Fosfomycin and nitrofurantoin: classic antibiotics and perspectives

Antibiotics are essential molecules for the treatment and prophylaxis of many infectious diseases. However, drugs that combat microbial infections can become a human health threat due to their high and often indiscriminate consumption, considered one of the factors of antimicrobial resistance (AMR) emergence. The AMR crisis, the decrease in new drug development by the pharmaceutical industry, and reduced economic incentives for research have all reduced the options for treating infections, and new strategies are necessary, including the return of some traditional but "forgotten" antibiotics. However, prescriptions for these older drugs including nitrofurantoin and oral fosfomycin, have been based on the results of pioneer studies, and the limited knowledge generated 50-70 years ago may not be enough. To avoid harming patients and further increasing multidrug resistance, systematic evaluation is required, mainly for the drugs prescribed for community-acquired infections, such as urinary tract infections (UTI). Therefore, this review has the objective of reporting the use of two classic drugs from the nitrofuran and phosphonic acid classes for UTI control nowadays. Furthermore, we also explore new approaches used for these antibiotics, including new combination regimes for spectral amplification, and the prospects for reducing bacterial resistance in the fight against bacteria responsible for UTI.

Effective removal of the herbicide glyphosate by the kelp Saccharina japonica female gametophytes from saline waters and its mechanism elucidation

Glyphosate has been widely and extensively used for weed control because of its excellent herbicidal profile and low costs. However, more than 750 glyphosate products are on the market and are increasingly regarded as water pollutants as they cause adverse effects on aquatic life. Dry cell weight and photosynthesis of Saccharina japonica female gametophytes increased when glyphosate was used as the sole phosphorus source at the concentration of less than 20 mg L-1. Nuclear magnetic resonance (NMR) analysis unambiguously confirmed that female gametophytes of the brown alga Saccharina japonica have the capability of breaking the C-P bond of glyphosate to orthophosphate, which finds the enormous potential of the most common seaweed to degrade the most widely used herbicide in the world. Furthermore, this is the first report on the use of glyphosate as the sole phosphorus source for the growth of eukaryotic cells. Because of the wide distribution and relatively easy cultivation of the fast-growing brown alga Saccharina japonica on the coast, our results set a promising stage for developing large macroalgae-based biotechnologies that can be applied for the remediation of contaminated seawater, which is greener and more cost-effective than conventional treatment methods.

Biosynthesis of fosfomycin in pseudomonads reveals an unexpected enzymatic activity in the metallohydrolase superfamily

The epoxide-containing phosphonate natural product fosfomycin is a broad-spectrum antibiotic used in the treatment of cystitis. Fosfomycin is produced by both the plant pathogen Pseudomonas syringae and soil-dwelling streptomycetes. While the streptomycete pathway has recently been fully elucidated, the pseudomonad pathway is still mostly elusive. Through a systematic evaluation of heterologous expression of putative biosynthetic enzymes, we identified the central enzyme responsible for completing the biosynthetic pathway in pseudomonads. The missing transformation involves the oxidative decarboxylation of the intermediate 2-phosphonomethylmalate to a new intermediate, 3-oxo-4-phosphonobutanoate, by PsfC. Crystallographic studies reveal that PsfC unexpectedly belongs to a new class of diiron metalloenzymes that are part of the polymerase and histidinol phosphatase superfamily.

Overall Retention of Methyl Stereochemistry during B12-Dependent Radical SAM Methyl Transfer in Fosfomycin Biosynthesis

Methylcobalamin-dependent radical S-adenosylmethionine (SAM) enzymes methylate non-nucleophilic atoms in a range of substrates. The mechanism of the methyl transfer from cobalt to the receiving atom is still mostly unresolved. Here we determine the stereochemical course of this process at the methyl group during the biosynthesis of the clinically used antibiotic fosfomycin. In vitro reaction of the methyltransferase Fom3 using SAM labeled with 1H, 2H, and 3H in a stereochemically defined manner, followed by chemoenzymatic conversion of the Fom3 product to acetate and subsequent stereochemical analysis, shows that the overall reaction occurs with retention of configuration. This outcome is consistent with a double-inversion process, first in the SN2 reaction of cob(I)alamin with SAM to form methylcobalamin and again in a radical transfer of the methyl group from methylcobalamin to the substrate. The methods developed during this study allow high-yield in situ generation of labeled SAM and recombinant expression and purification of the malate synthase needed for chiral methyl analysis. These methods facilitate the broader use of in vitro chiral methyl analysis techniques to investigate the mechanisms of other novel enzymes.

QM/MM Study of the Fosfomycin Resistance Mechanism Involving FosB Enzyme

Multidrug-resistant organisms contain antibiotic-modifying enzymes that facilitate resistance to a variety of antimicrobial compounds. Particularly, the fosfomycin (FOF) drug can be structurally modified by several FOF-modifying enzymes before it reaches the biological target. Among them, FosB is an enzyme that utilizes l-cysteine or bacillithiol in the presence of a divalent metal to open the epoxide ring of FOF and, consequently, inactivate the drug. Here, we have used hybrid quantum mechanics/molecular mechanics (QM/MM) and molecular dynamics (MD) simulations to explore the mechanism of the reaction involving FosB and FOF. The calculated free-energy profiles show that the cost to open the epoxide ring of FOF at the C2 atom is ∼3.0 kcal/mol higher than that at the C1 atom. Besides, our QM/MM MD results revealed the critical role of conformation change of Cys9 and Asn50 to release the drug from the active site. Overall, the present study provides insights into the mechanism of FOF-resistant proteins.

In Vitro Susceptibility of Multi-Drug Resistant Klebsiellapneumoniae Strains Causing Nosocomial Infections to Fosfomycin. A Comparison of Determination Methods

INTRODUCTION

Over the past few decades, Klebsiella pneumoniae strains increased their pathogenicity and antibiotic resistance, thereby becoming a major therapeutic challenge. One of the few available therapeutic options seems to be intravenous fosfomycin. Unfortunately, the determination of sensitivity to fosfomycin performed in hospital laboratories can pose a significant problem. Therefore, the aim of the present research was to evaluate the activity of fosfomycin against clinical, multidrug-resistant Klebsiella pneumoniae strains isolated from nosocomial infections between 2011 and 2020, as well as to evaluate the methods routinely used in hospital laboratories to assess bacterial susceptibility to this antibiotic.

MATERIALS AND METHODS

43 multidrug-resistant Klebsiella strains isolates from various infections were tested. All the strains had ESBL enzymes, and 20 also showed the presence of carbapenemases. Susceptibility was determined using the diffusion method (E-test) and the automated system (Phoenix), which were compared with the reference method (agar dilution).

RESULTS

For the reference method and for the E-test, the percentage of strains sensitive to fosfomycin was 65%. For the Phoenix system, the percentage of susceptible strains was slightly higher and stood at 72%. The percentage of fosfomycin-resistant strains in the Klebsiella carbapenemase-producing group was higher (45% for the reference method and E-test and 40% for the Phoenix method) than in carbapenemase-negative strains (25%, 25%, and 20%, respectively). Full (100%) susceptibility categorical agreement was achieved for the E-test and the reference method. Agreement between the automated Phoenix system and the reference method reached 86%.

CONCLUSIONS

Fosfomycin appears to be the antibiotic with a potential for use in the treatment of infections with multidrug-resistant Klebsiella strains. Susceptibility to this drug is exhibited by some strains, which are resistant to colistin and carbapenems. The E-test, unlike the Phoenix method, can be an alternative to the reference method in the routine determination of fosfomycin susceptibility, as it shows agreement in terms of sensitivity categories and only slight differences in MIC values. The Phoenix system, in comparison to the reference method, shows large discrepancies in the MIC values and in the susceptibility category.

C-P Natural Products as Next-Generation Herbicides: Chemistry and Biology of Glufosinate

In modern agriculture and weed management practices, herbicides have been widely used to control weeds effectively and represent more than 50% of commercial pesticides applied in the world. Herbicides with unique mechanisms of actions (MOA) have historically been discovered and commercialized every two or three years from the 1950s to the 1980s. However, this trend lowered dramatically as no herbicide with a novel MOA has been marketed for more than 30 years. The fast-growing resistance to commercial herbicides has reignited the agricultural chemical industry interest in new structural scaffolds targeting novel sites in plants. Carbon-phosphorus bonds (C-P) containing natural products (NPs) have played an essential role in herbicide discovery as the chemical diversity, and the promising bioactivity of natural C-P phytotoxins can provide exciting opportunities for the discovery of both natural and semisynthetic herbicides with novel targets. Among commercial herbicides, glyphosate (Roundup), a famous C-P containing herbicide, is by far the most universally used herbicide worldwide. Furthermore, glufosinate is one of the most widely used natural herbicides in the world. Therefore, C-P NPs are a treasure for discovering new herbicides with novel mechanisms of actions (MOAs). Here, we present an overview of the chemistry and biology of glufosinate including isolation and characterization, mode of action, herbicidal use, biosynthesis, and chemical synthesis since its discovery in order to not only help scientists reassess the role of this famous herbicide in the field of agrichemical chemistry but also build a new stage for discovering novel C-P herbicides with new MOAs.