-lactam antibiotics: their physicochemical properties and biological activities in relation to structure

Halogenated Antimicrobial Agents to Combat Drug-Resistant Pathogens

Antimicrobial resistance presents us with a potential global crisis as it undermines the abilities of conventional antibiotics to combat pathogenic microbes. The history of antimicrobial agents is replete with examples of scaffolds containing halogens. In this review, we discuss the impacts of halogen atoms in various antibiotic types and antimicrobial scaffolds and their modes of action, structure-activity relationships, and the contributions of halogen atoms in antimicrobial activity and drug resistance. Other halogenated molecules, including carbohydrates, peptides, lipids, and polymeric complexes, are also reviewed, and the effects of halogenated scaffolds on pharmacokinetics, pharmacodynamics, and factors affecting antimicrobial and antivirulence activities are presented. Furthermore, the potential of halogenation to circumvent antimicrobial resistance and rejuvenate impotent antibiotics is addressed. This review provides an overview of the significance of halogenation, the abilities of halogens to interact in biomolecular settings and enhance pharmacological properties, and their potential therapeutic usages in preventing a postantibiotic era. SIGNIFICANCE STATEMENT: Antimicrobial resistance and the increasing impotence of antibiotics are critical threats to global health. The roles and importance of halogen atoms in antimicrobial drug scaffolds have been established, but comparatively little is known of their pharmacological impacts on drug resistance and antivirulence activities. This review is the first to extensively evaluate the roles of halogen atoms in various antibiotic classes and pharmacological scaffolds and to provide an overview of their ability to overcome antimicrobial resistance.

Ampicillin Stability in a Portable Elastomeric Infusion Pump: A Step Forward in Outpatient Parenteral Antimicrobial Therapy

Outpatient parenteral antimicrobial therapy (OPAT) with continuous infusion pumps is postulated as a very promising solution to treat complicated infections, such as endocarditis or osteomyelitis, that require patients to stay in hospital during extended periods of time, thus reducing their quality of life and increasing the risk of complications. However, stability studies of drugs in elastomeric devices are scarce, which limits their use in OPAT. Therefore, we evaluated the stability of ampicillin in sodium chloride 0.9% at two different concentrations, 50 and 15 mg/mL, in an elastomeric infusion pump when stored in the refrigerator and subsequently in real-life conditions at two different temperatures, 25 and 32 °C, with and without the use of a cooling device. The 15 mg/mL ampicillin is stable for up to 72 h under refrigeration, allowing subsequent dosing at 25 °C for 24 h with and without a cooling device, but at 32 °C its concentration drops below 90% after 8 h. In contrast, 50 mg/mL ampicillin only remains stable for the first 24 h under refrigeration, and subsequent administration at room temperature is not possible, even with the use of a cooling system. Our data support that 15 mg/mL AMP is suitable for use in OPAT if the volume and rate of infusion are tailored to the dosage needs of antimicrobial treatments.

The Antimicrobial Activity of Micron-Thin Sol-Gel Films Loaded with Linezolid and Cefoxitin for Local Prevention of Orthopedic Prosthesis-Related Infections

Orthopedic prosthesis-related infections (OPRI) are an essential health concern. OPRI prevention is a priority and a preferred option over dealing with poor prognosis and high-cost treatments. Micron-thin sol-gel films have been noted for a continuous and effective local delivery system. This study aimed to perform a comprehensive in vitro evaluation of a novel hybrid organic-inorganic sol-gel coating developed from a mixture of organopolysiloxanes and organophosphite and loaded with different concentrations of linezolid and/or cefoxitin. The kinetics of degradation and antibiotics release from the coatings were measured. The inhibition of biofilm formation of the coatings against Staphylococcus aureus, S. epidermidis, and Escherichia coli strains was studied, as well as the cell viability and proliferation of MC3T3-E1 osteoblasts. The microbiological assays demonstrated that sol-gel coatings inhibited the biofilm formation of the evaluated Staphylococcus species; however, no inhibition of the E. coli strain was achieved. A synergistic effect of the coating loaded with both antibiotics was observed against S. aureus. The cell studies showed that the sol-gels did not compromise cell viability and proliferation. In conclusion, these coatings represent an innovative therapeutic strategy with potential clinical use to prevent staphylococcal OPRI.

An Electrochemical Approach to Directed Fluorination

Electrosynthesis has made a revival in the field of organic chemistry and, in particular, radical-mediated reactions. Herein, we report a simple directed, electrochemical C-H fluorination method. Employing a dabconium mediator, commercially available Selectfluor, and RVC electrodes, we provide a range of steroid-based substrates with competent regioselective directing groups, including enones, ketones, and hydroxy groups, as well as never reported before lactams, imides, lactones, and esters.

Epibenthic microbial mats behavior as phosphorus sinks or sources in relation to biological and physicochemical conditions

Microbial mats are complex microecosystems that have shown promise as possible green filters to remediate polluted seawater. This usage would possibly require changing the natural conditions under which these microbial mats prosper in order to maximize their contact with the water. Thus, it is necessary to evaluate the adaptation of the mats to different environmental conditions, while monitoring their short-term efficiency at nutrient removal. To that aim, epibenthic microbial mats collected from a tidal flat in the Bahía Blanca Estuary, were incubated under different flooding conditions (periodically exposed to the air or continuously flooded), with and without the addition of a high phosphorus concentration (5 mg PO₄^3- L^-1), and with and without the presence of penicillin. This last condition was added to understand the influence of penicillin-sensitive microbes on cyanobacteria and diatom communities and their importance for P remediation. The presence of high P concentrations as well as the continual flooding of the mats resulted in the decrease of the dominant cyanobacterium, Coleofasciculus (Microcoleus) chthonoplastes, giving rise to the dominance of other genera such as Arthrospira sp. Or Oscillatoria sp., depending on the presence or absence of the antibiotic, respectively. Water P removal was highly efficient (60-87%) when the mats were treated with the high-P water. However, microbial mat behavior changed from P sink to source when mats where incubated in seawater with no P addition, suggesting that mats can both function as P sinks and sources, depending on the condition of the water they come in contact with.

Recent progress in Fenton/Fenton-like reactions for the removal of antibiotics in aqueous environments

The frequent use of antibiotics allows them to enter aqueous environments via wastewater, and many types of antibiotics accumulate in the environment due to difficult degradation, causing a threat to environmental health. It is crucial to adopt effective technical means to remove antibiotics in aqueous environments. The Fenton reaction, as an effective organic pollution treatment technology, is particularly suitable for the treatment of antibiotics, and at present, it is one of the most promising advanced oxidation technologies. Specifically, rapid Fenton oxidation, which features high removal efficiency, thorough reactions, negligible secondary pollution, etc., has led to many studies on using the Fenton reaction to degrade antibiotics. This paper summarizes recent progress on the removal of antibiotics in aqueous environments by Fenton and Fenton-like reactions. First, the applications of various Fenton and Fenton-like oxidation technologies to the removal of antibiotics are summarized; then, the advantages and disadvantages of these technologies are further summarized. Compared with Fenton oxidation, Fenton-like oxidations exhibit milder reaction conditions, wider application ranges, great reduction in economic costs, and great improved cycle times, in addition to simple and easy recycling of the catalyst. Finally, based on the above analysis, we discuss the potential for the removal of antibiotics under different application scenarios. This review will enable the selection of a suitable Fenton system to treat antibiotics according to practical conditions and will also aid the development of more advanced Fenton technologies for removing antibiotics and other organic pollutants.

Quantum chemical prediction of effects of temperature on hydrolysis rate of penicillin under weakly acidic condition

Temperature and pH are important factors affecting the hydrolysis of β-lactam antibiotics in water environments. However, the determination of hydrolysis kinetics and pathways is experimentally challenging, particularly in low temperature aqueous solutions because of time and cost constraints. In this study, an equation was employed to correct the Gibbs energy calculated in aqueous solutions by density functional theory methods to predict the effect of temperature on the hydrolysis kinetics and pathways of penicillin G. The results indicate that the most likely hydrolysis mechanism involves the opening of the β-lactam ring of anionic penicillin G protonated at the β-lactam oxygen atom with the participation of the carboxyl group and a water molecule. The results also suggest that the carboxyl group of β-lactam antibiotics was crucial for the hydrogen transfer. The predicted rate constants were of the same order of magnitude as the experimental values obtained under comparable pH and temperature conditions. Therefore, the quantum chemical methodology described herein can be potentially employed to determine pH- and temperature-based two-dimensional hydrolysis rate models, which can enable the prediction of the β-lactam antibiotics persistence in frigid waters.

Occurrence and removal of antibiotics, antibiotic resistance genes, and bacterial communities in hospital wastewater

Hospital wastewater contains a variety of human antibiotics and pathogens, which makes the treatment of hospital wastewater essential. However, there is a lack of research on these pollutants at hospital wastewater treatment plants. In this study, the characteristics and removal of antibiotics and antibiotic resistance genes (ARGs) in the independent treatment processes of hospitals of different scales (primary hospital, H1; secondary hospital, H2; and tertiary hospital, H3) were investigated. The occurrence of antibiotics and ARGs in wastewater from three hospitals varied greatly. The first-generation cephalosporin cefradine was detected at a concentration of 2.38 μg/L in untreated wastewater from H1, while the fourth-generation cephalosporin cefepime had the highest concentration, 540.39 μg/L, at H3. Ofloxacin was detected at a frequency of 100% and had removal efficiencies of 44.2%, 51.5%, and 81.6% at H1, H2, and H3, respectively. The highest relative abundances of the β-lactam resistance gene bla_GES-1 (1.77×10^-3 copies/16S rRNA), the quinolone resistance gene qnrA (8.81×10^-6 copies/16S rRNA), and the integron intI1 (1.86×10^-4 copies/16S rRNA) were detected in the treated wastewater. The concentrations of several ARGs were increased in the treated wastewater (e.g. bla_OXA-1, bla_OXA-10, and bla_TEM-1). Several pathogenic or opportunistic bacteria (e.g. Acinetobacter, Klebsiella, Aeromonas, and Pseudomonas) were observed at high relative abundances in the treated wastewater. These results suggested the co-occurrence of antibiotics, ARGs, and antibiotic-resistant pathogens in hospital wastewater, and these factors may spread into the receiving aquatic environment.

Photocatalytic degradation of amoxicillin from aqueous solutions by titanium dioxide nanoparticles loaded on graphene oxide

The photocatalytic degradation of amoxicillin (AMX) by titanium dioxide nanoparticles loaded on graphene oxide (GO/TiO₂) was evaluated under UV light. Experimental results showed that key parameters such as initial pH, GO/TiO₂ dosage, UV intensity, and initial AMX concentration had a significant effect on AMX degradation. Compared to the photolysis and adsorption processes, the AMX degradation efficiency was obtained to be more than 99% at conditions including pH of 6, the GO/TiO₂ dosage of 0.4 g/L, the AMX concentration of 50 mg/L, and the intensity of 36 W. Trapping tests showed that all three hydroxyl radical (OH^•), superoxide radical (O₂^•-), and hole (h⁺) were produced in the photocatalytic process; however, h⁺ plays a major role in AMX degradation. Under UV irradiation, GO/TiO₂ showed excellent stability and recyclability for 4 consecutive reaction cycles. The analysis of total organic carbon (TOC) suggested that AMX could be well degraded into CO₂ and H₂O. The formation of NH₄⁺, NO₃^-, and SO₄^2- as a result of AMX degradation confirmed the good mineralization of AMX in the GO/TiO₂/UV process. The toxicity of the inlet and outlet samples of the process has been investigated by cultivation of Escherichia coli and Streptococcus faecalis, and the results showed that the condition is suitable for the growth of organisms. The photocatalytic degradation mechanism was proposed based on trapping and comparative tests. Based on the results, the GO/TiO₂/UV process can be considered as a promising technique for AMX degradation due to photocatalyst stability, high mineralization efficiency, and effluent low toxicity.

Green and efficient degradation of cefoperazone sodium by Bi4O5Br2 leading to the production of non-toxic products: Performance and degradation pathway

Photocatalytic process represents a promising approach to overcome the pollution challenge associated with the antibiotics-containing wastewater. This study provides a green, efficient and novel approach to remove cephalosporins, particularly cefoperazone sodium (CFP). Bi₄O₅Br₂ was chosen for the first time to systematically study its degradation for CFP, including the analysis of material structure, degradation performance, the structure and toxicity of the transformation products, etc. The degradation rate results indicated that Bi₄O₅Br₂ had an excellent catalytic activity leading to 78% CFP removal compared with the pure BiOBr (38%) within 120 min of visible light irradiation. In addition, the Bi₄O₅Br₂ presents high stability and good organic carbon removal efficiency. The effects of the solution pH (3.12 - 8.75) on catalytic activity revealed that CFP was mainly photocatalyzed under acidic conditions and hydrolyzed under alkaline conditions. Combined with active species and degradation product identification, the photocatalytic degradation pathways of CFP by Bi₄O₅Br₂ was proposed, including hydrolysis, oxidation, reduction and decarboxylation. Most importantly, the identified products were all hydrolysis rather than oxidation byproducts transformed from the intermediate of β-lactam bond cleavage in CFP molecule, quite different from the mostly previous studies. Furthermore, the final products were demonstrated to be less toxic through the toxicity analysis. Overall, this study illustrates the detailed mechanism of CFP degradation by Bi₄O₅Br₂ and confirms Bi₄O₅Br₂ to be a promising material for the photodegradation of CFP.

Catalytic hydrolysis of β-lactam antibiotics via MOF-derived MgO nanoparticles embedded on nanocast silica

The antibiotics abuse and the proliferation of antibiotic-resistant bacteria in the environment have a severe impact on both human health and ecosystem. In this study, a silica-nanocasting method was applied in Mg-MOF-74 template to generate a series of MgO/SiO₂ catalysts for the hydrolysis of β-lactam antibiotics. The Mg-based subunits in MOF-74 were converted to highly dispersed MgO nanoparticles with controllable particle size. MgO/SiO₂-80 with the smallest MgO particle size exhibits the best catalytic performance in the hydrolysis of four β-lactam antibiotics. The kinetics study reveals the higher degradation rate and lower activation energy of MgO/SiO₂-80 than other benchmark solid base catalysts. The proposed mechanism suggests that small MgO particle size provides more accessible oxygen anions with high proton affinity for the cleavage of the β-lactam ring, so that all hydrolytic products lose antimicrobial activity. The MgO/SiO₂-80 serves as the potential high-performance solid base catalyst for the real-world antibiotic wastewater treatment.

Stability of β-lactam antibiotics in bacterial growth media

Laboratory assays such as MIC tests assume that antibiotic molecules are stable in the chosen growth medium-but rapid degradation has been observed for antibiotics including β-lactams under some conditions in aqueous solution. Degradation rates in bacterial growth medium are less well known. Here, we develop a 'delay time bioassay' that provides a simple way to estimate antibiotic stability in bacterial growth media, using only a plate reader and without the need to measure the antibiotic concentration directly. We use the bioassay to measure degradation half-lives of the β-lactam antibiotics mecillinam, aztreonam and cefotaxime in widely-used bacterial growth media based on MOPS and Luria-Bertani (LB) broth. We find that mecillinam degradation can occur rapidly, with a half-life as short as 2 hours in MOPS medium at 37°C and pH 7.4, and 4-5 hours in LB, but that adjusting the pH and temperature can increase its stability to a half-life around 6 hours without excessively perturbing growth. Aztreonam and cefotaxime were found to have half-lives longer than 6 hours in MOPS medium at 37°C and pH 7.4, but still shorter than the timescale of a typical minimum inhibitory concentration (MIC) assay. Taken together, our results suggest that care is needed in interpreting MIC tests and other laboratory growth assays for β-lactam antibiotics, since there may be significant degradation of the antibiotic during the assay.

Development of a method of analysis for profiling of the impurities in phenoxymethylpenicillin potassium based on the analytical quality by design concept combined with the degradation mechanism of penicillins

Accurate analysis of all of the impurities present in a substance is critical for controlling the impurity profiles of drugs. Penicillins can easily yield a formidable array of degradation-related impurities (DRIs) with significantly different polarities and charge properties, which renders identifying each one a complicated matter. In this work, phenoxymethylpenicillin potassium (Pen V) was selected to find a way to quickly establish a robust analysis method for the impurity profiling of penicillin. Based on the analytical quality by design (AQbD) concept and the degradation mechanism of the drug, structures of all of the DRIs were first proposed. Then Pen V and its detected DRIs were separated and identified by liquid chromatography-tandem mass spectrometry method (LC-MS). Characteristic fragment ions and mass fragmentation process of Pen V and its detected DRIs were summarized. In addition, a quantitative structure-retention relationship (QSRR) model was constructed to predict the retention times of undetected impurities and to evaluate whether the chromatographic system can separate them. Finally, a stability-indicating high-performance liquid chromatography (HPLC) method was developed that can separate all of the DRIs of Pen V.

A Natural Deep Eutectic Solvent Formulated to Stabilize β-Lactam Antibiotics

β-lactam antibiotics, such as penicillin share a very unstable chemical structure. In water-based solutions, such as those used for clinical applications, the β-lactam ring is readily opened due to a nucleophilic or electrophilic attack, leading to the loss of antimicrobial activity. Since the achievement and maintenance of optimum therapeutic levels of β-lactam antibiotics is critical for the resolution of many infectious clinical situations, and to avoid antibiotic resistance generation, the design of new non-aqueous dosage forms is urgent. Recently, natural deep eutectic solvents (NADES) have emerged as alternative non-toxic and non-aqueous solvents for different biomedical applications. In this work, we formulated and characterized a NADES composed by betaine and urea (BU). Using this solvent, we evaluated the stability of clavulanic acid (CLV) and imipenem (IMP) and characterized their antimicrobial activities calculating the minimal inhibitory concentration. Characterization of BU solvent by infrared spectroscopy (IR) and nuclear magnetic resonance spectroscopy (NMR) indicated that the obtained solvent has a microstructure mainly based on hydrogen bonding interactions and water addition strongly affects its dynamic. The stability of β-lactam antibiotic IMP and CLV using this solvent was increased by 7 fold and 2.5 fold respectively compared to water when analysed seven days after being dissolved. Microbiological assays showed that antibacterial activity at day seven was significantly decreased for both CLV and IMP when dissolved in water, while no change in their antibacterial properties was observed when antibiotics were dissolved in BU. The increased stability of IMP and CLV in BU may be related to the inert behaviour of the solvent and the higher dynamic restriction that helps antibiotics to maintain a more stable conformation. These data suggest the potential use of BU as a solvent to prevent degradation of β-lactam antibiotics.

Pharmaceuticals in the aquatic environments: Evidence of emerged threat and future challenges for marine organisms

Pharmaceuticals are nowadays recognized as a threat for aquatic ecosystems. The growing consumption of these compounds and the enhancement of human health in the past two decades have been paralleled by the continuous input of such biologically active molecules in natural environments. Waste water treatment plants (WWTPs) have been identified as a major route for release of pharmaceuticals in aquatic bodies where concentrations ranging from ng/L to μg/L are ubiquitously detected. Since medicines principles are designed to be effective at very low concentrations, they have the potential to interfere with biochemical and physiological processes of aquatic species over their entire life cycle. Investigations on occurrence, bioaccumulation and effects in non target organisms are fragmentary, particularly for marine ecosystems, and related to only a limited number over the 4000 substances classified as pharmaceuticals: hence, there is a urgent need to prioritize the environmental sustainability of the most relevant compounds. The aim of this review is to summarize the main adverse effects documented for marine species exposed in both field and laboratory conditions to different classes of pharmaceuticals including non-steroidal anti-inflammatory drugs, psychiatric, cardiovascular, hypocholesterolaemic drugs, steroid hormones and antibiotics. Despite a great scientific advancement has been achieved, our knowledge is still limited on pharmaceuticals behavior in chemical mixtures, as well as their interactions with other environmental stressors. Complex ecotoxicological effects are increasingly documented and multidisciplinary, integrated approaches will be helpful to clarify the environmental hazard of these "emerged" pollutants in marine environment.

Elimination of Isoxazolyl-Penicillins antibiotics in waters by the ligninolytic native Colombian strain Leptosphaerulina sp. considerations on biodegradation process and antimicrobial activity removal

In this work, Leptosphaerulina sp. (a Colombian native fungus) significantly removed three Isoxazolyl-Penicillin antibiotics (IP): oxacillin (OXA, 16000 μg L^-1), cloxacillin (CLX, 17500 μg L^-1) and dicloxacillin (DCX, 19000 μg L^-1) from water. The biological treatment was performed at pH 5.6, 28 °C, and 160 rpm for 15 days. The biotransformation process and lack of toxicity of the final solutions (antibacterial activity (AA) and cytotoxicity) were tested. The role of enzymes in IP removal was analysed through in vitro studies with enzymatic extracts (crude and pre-purified) from Leptosphaerulina sp., commercial enzymes and enzymatic inhibitors. Furthermore, the applicability of mycoremediation process to a complex matrix (simulated hospital wastewater) was evaluated. IP were considerably abated by the fungus, OXA was the fastest degraded (day 6), followed by CLX (day 7) and DCX (day 8). Antibiotics biodegradation was associated to laccase and versatile peroxidase action. Assays using commercial enzymes (i.e. laccase from Trametes versicolor and horseradish peroxidase) and inhibitors (EDTA, NaCl, sodium acetate, manganese (II) ions) confirmed the significant role of enzymatic transformation. Whereas, biomass sorption was not an important process in the antibiotics elimination. Evaluation of AA against Staphylococcus aureus ATCC 6538 revealed that Leptosphaerulina sp. also eliminated the AA. In addition, the cytotoxicity assay (MTT) on the HepG2 cell line demonstrated that the IP final solutions were non-toxic. Finally, Leptosphaerulina sp. eliminated OXA and its AA from synthetic hospital wastewater at 6 days. All these results evidenced the potential of Leptosphaerulina sp. mycoremediation as a novel environmentally friendly process for the removal of IP from aqueous systems.

Cu(II)-catalyzed degradation of ampicillin: effect of pH and dissolved oxygen

Cu(II)-catalyzed hydrolysis of β-lactam antibiotics has been well-identified and recognized as the key mechanism of antibiotic degradation. However, the overlooked Cu(II) oxidation susceptibly also plays an important role comparably with hydrolysis. This study evaluated the roles of hydrolysis and oxidation in Cu(II)-catalyzed degraded ampicillin (AMP), as a typical β-lactam antibiotic, under relevant environmental conditions (pH 5.0, 7.0, and 9.0; oxygen 0.2 and 6.2 mg/L). Under AMP and Cu(II) molar ratio of 1:1, AMP degradation was the fastest at pH 9.0, followed by pH 5.0 and pH 7.0. The facilitation of oxygen on AMP degradation was notable at pH 5.0 and 7.0 rather than pH 9.0. AMP degradation rate increased from 21.8% in 0.2 mg/L O₂ solution to 85.9% in 6.2 mg/L O₂ solution at pH 7.0 after 4-h reaction. AMP oxidation was attributed to both oxygen-derived Cu(I)/Cu(II) cycle and intermediate reactive oxygen species (HO^. and O₂^.-). Several intermediate and final products in AMP degradation were firstly identified by LC-quadrupole time-of-flight-MS analysis. Phenylglycine primary amine on the AMP structure was the essential complexation site to proceed with the oxidation reaction. The oxidation of AMP preferentially occurred on the β-lactam structure. The inherent mechanisms related to pH and oxygen conditions were firstly investigated, which could enhance the understanding of both oxidation and hydrolysis mechanisms in AMP degradation. This study not only has an important implication in predicting β-lactam antibiotic transformation and fate in natural environment but also benefits the developing of strategies of antibiotic control to reduce the environmental risk.

Residue depletion of amoxicillin and its major metabolites in eggs

The depletion of amoxicillin (AMO) and its major metabolites, amoxicilloic acid (AMA) and amoxicillin-diketopiperazine-2',5'-dione (DIKETO) in the albumen, yolk and whole egg was studied after the oral dose of AMO (25 and 50 mg/kg body weight) to laying hens once per day for five consecutive days. Egg samples were prepared by a simple liquid-liquid extraction procedure with acetonitrile and saturated methylene chloride and analysed using liquid chromatography-tandem mass spectrometry. The results showed that AMO, AMA and DIKETO residues were mainly distributed in the yolk, where particularly high concentrations of AMO and DIKETO were found, whereas the albumen contained high concentrations of AMA. This distribution suggested that AMO and DIKETO were depleted slowly in yolk, whereas AMA was depleted slowly in albumen. The amount of AMO residue positively correlated with the dose, and the theoretical withdrawal times, which were calculated based on the residue level falling below a safe limit, were 5.21 and 7.67 days at AMO doses of 25 and 50 mg/kg, respectively. Moreover, the theoretical withdrawal times for all residues in the whole egg were 8.00 and 9.11 days at doses of 25 and 50 mg/kg, respectively. Our findings suggested that 9 days was an appropriate withdrawal time for the use of AMO in laying hens.

Identification of Penicillin G Metabolites under Various Environmental Conditions Using UHPLC-MS/MS

In this work, we investigate the stability of penicillin G in various conditions including acidic, alkaline, natural acidic matrices and after treatment of citrus trees that are infected with citrus greening disease. The identification, confirmation, and quantitation of penicillin G and its various metabolites were evaluated using two UHPLC-MS/MS systems with variable capabilities (i.e., Thermo Q Exactive Orbitrap and Sciex 6500 QTrap). Our data show that under acidic and alkaline conditions, penicillin G at 100 ng/mL degrades quickly, with a determined half-life time of approximately 2 h. Penillic acid, penicilloic acid, and penilloic acid are found to be the most abundant metabolites of penicillin G. These major metabolites, along with isopenillic acid, are found when penicillin G is used for treatment of citrus greening infected trees. The findings of this study will provide insight regarding penicillin G residues in agricultural and biological applications.

Change in hydrophilicity of penicillins during advanced oxidation by radiolytically generated OH compromises the elimination of selective pressure on bacterial strains

Advanced oxidation processes are promising technologies for removal of antibiotic residues from wastewater in terms of their high efficacy. However, recent studies have reported the remaining antibacterial activity of the products at early-stages of treatment. The present study investigates the effect of such products of model β-lactams (amoxicillin, ampicillin, cloxacillin) on bacteria introducing structure-based, and biological approaches involving Gram-positive and Gram-negative bacterial strains. Chemical analysis revealed the destruction of the β-lactam pharmacophore in competition with the reaction at the aromatic ring. Multisite attack occurs on the penicillin skeleton producing OH-substituted products. The enhanced hydrophilicity confers higher diffusion rate through the porin channels of Gram-negative bacteria and through the hydrophilic cell wall of Gram-positive species. Accordingly, an increase in acute toxicity of treated samples was observed at the beginning of the treatment. The same tendency was observed for target-specific antimicrobial activity investigated with antibiotic susceptibility testing (agar-diffusion, bacterial growth). Prolonged treatments yielded products, e.g. polyhydroxylated phenolic compounds, being also deleterious for bacteria. Therefore, the advanced oxidation process should be judiciously optimized.

Maturity and security assessment of pilot-scale aerobic co-composting of penicillin fermentation dregs (PFDs) with sewage sludge

In this work, penicillin fermentation dregs (PFDs) and sewage sludge (SWS) were co-composted to analyze the possibility of recycling nutrients in PFDs. The temperature was maintained above 55°C for more than 3 days, and the final electrical conductivity (EC), pH and C/N all met the national standards in maturity. A nearly 100% removal of the residual penicillin was achieved, and the seed germination index (GI) increased from 0.02% to 83.54±3.1% by the end of the composting process. However, monitoring the quantity of antibiotic resistance genes (ARGs) showed that the logarithm of the number of copies of blaTEM increased from 4.17±0.19 at the initial phase to 8.92±0.27 by the end of the composting process, which means that there is a high risk for land use when using PFD compost products.

Solvent Effect on the Photolysis of Riboflavin

The kinetics of photolysis of riboflavin (RF) in water (pH 7.0) and in organic solvents (acetonitrile, methanol, ethanol, 1-propanol, 1-butanol, ethyl acetate) has been studied using a multicomponent spectrometric method for the assay of RF and its major photoproducts, formylmethylflavin and lumichrome. The apparent first-order rate constants (k obs) for the reaction range from 3.19 (ethyl acetate) to 4.61 × 10(-3) min(-1) (water). The values of k obs have been found to be a linear function of solvent dielectric constant implying the participation of a dipolar intermediate along the reaction pathway. The degradation of this intermediate is promoted by the polarity of the medium. This indicates a greater stabilization of the excited-triplet states of RF with an increase in solvent polarity to facilitate its reduction. The rate constants for the reaction show a linear relation with the solvent acceptor number indicating the degree of solute-solvent interaction in different solvents. It would depend on the electron-donating capacity of RF molecule in organic solvents. The values of k obs are inversely proportional to the viscosity of the medium as a result of diffusion-controlled processes.

Cu(II)-catalyzed transformation of benzylpenicillin revisited: the overlooked oxidation

Penicillins, a class of widely used β-lactam antibiotics, are known to be susceptible to catalyzed hydrolysis by metal ions such as Cu(II). However, new results in this study strongly indicate that the role of Cu(II) is not merely a hydrolysis catalyst but also an oxidant. When benzylpenicillin (i.e., penicillin G (PG)) was exposed to Cu(II) ion at an equal molar ratio and pH 7, degradation of PG occurred rapidly in the oxygen-rich solution but gradually slowed down to a halt in the oxygen-limited solution. In-depth studies revealed that Cu(II) catalyzed hydrolysis of PG to benzylpenicilloic acid (PA) and oxidized PA to yield phenylacetamide and other products. The availability of oxygen played the role in reoxidizing Cu(I) back to Cu(II), which sustained fast degradation of PG over time. The overall reaction was also influenced by pH, with Cu(II)-catalyzed hydrolysis of PG occurring throughout pH 5, 7 and 9, while Cu(II) oxidation of PA occurring at pH 7 and 9. Note that the potential of Cu(II) to oxidize penicillins was largely overlooked in the previous literature, and catalyzed hydrolysis was frequently assumed as the only reaction. This study is among the first to identify the dual roles of Cu(II) in the entire degradation process of PG and systematically investigate the overlooked oxidation reaction to elucidate the mechanism. The new mechanistic knowledge has important implications for many other β-lactam antibiotics for their interactions with Cu(II), and significantly improves the ability to predict the environmental fate and transformation products of PG and related penicillins in systems where Cu(II) species are also present.

Effect of acetate and carbonate buffers on the photolysis of riboflavin in aqueous solution: a kinetic study

The photolysis of riboflavin (RF) in the presence of acetate buffer (pH 3.8-5.6) and carbonate buffer (pH 9.2-10.8) has been studied using a multicomponent spectrophotometric method for the simultaneous assay of RF and its photoproducts. Acetate and carbonate buffers have been found to catalyze the photolysis reaction of RF. The apparent first-order rate constants for the acetate-catalyzed reaction range from 0.20 to 2.86 × 10(-4) s(-1) and for the carbonate-catalyzed reaction from 3.33 to 15.89 × 10(-4) s(-1). The second-order rate constants for the interaction of RF with the acetate and the carbonate ions range from 2.04 to 4.33 × 10(-4) M(-1) s(-1) and from 3.71 to 11.80 × 10(-4) M(-1) s(-1), respectively. The k-pH profile for the acetate-catalyzed reaction is bell shaped and for the carbonate-catalyzed reaction a steep curve. Both HCO3(-) and CO3(2-) ions are involved in the catalysis of the photolysis reaction in alkaline solution. The rate constants for the HCO3(-) and CO3(2-) ions catalyzed reactions are 0.72 and 1.38 × 10(-3) M(-1) s(-1), respectively, indicating a major role of CO3(2-) ions in the catalysis reaction. The loss of RF fluorescence in acetate buffer suggests an interaction between RF and acetate ions to promote the photolysis reaction. The optimum stability of RF solutions is observed in the pH range 5-6, which is suitable for pharmaceutical preparations.

pH and temperature effects on the hydrolysis of three β-lactam antibiotics: ampicillin, cefalotin and cefoxitin

An understanding of antibiotic hydrolysis rates is important for predicting their environmental persistence. Hydrolysis rates and Arrhenius constants were determined as a function of pH and temperature for three common β-lactam antibiotics, ampicillin, cefalotin, and cefoxitin. Antibiotic hydrolysis rates at pH4-9 at 25 °C, 50 °C, and 60 °C were quantified, and degradation products were identified. The three antibiotics hydrolyzed under ambient conditions (pH7 and 25 °C); half-lives ranged from 5.3 to 27 d. Base-catalyzed hydrolysis rates were significantly greater than acid-catalyzed and neutral pH hydrolysis rates. Hydrolysis rates increased 2.5- to 3.9-fold for a 10 °C increase in temperature. Based on the degradation product masses found, the likely functional groups that underwent hydrolysis were lactam, ester, carbamate, and amide moieties. Many of the proposed products resulting from the hydrolysis of ampicillin, cefalotin, and cefoxitin likely have reduced antimicrobial activity because many products contained a hydrated lactam ring. The results of this research demonstrate that β-lactam antibiotics hydrolyze under ambient pH and temperature conditions. Degradation of β-lactam antibiotics will likely occur over several weeks in most surface waters and over several days in more alkaline systems.

Antibiotic detoxification from synthetic and real effluents using a novel MTAB surfactant-montmorillonite (organoclay) sorbent

A novel organoclay (MTAB surfactant-montmorillonite) sorbent showed its potential for the removal of amoxicillin and ampicillin antibiotics from synthetic and real effluents.

Persistence and degradation of new β-lactam antibiotics in the soil and water environment

The development of new antibiotics with low environmental persistence is of utmost importance in contrasting phenomena of antibiotic resistance. In this study, the persistence of two newly synthesized monocyclic β-lactam antibiotics: (2R)-1-(methylthio)-4-oxoazetidin-2-yl acetate, P1, and (2R,3R)-3-((1R)-1-(tert-butyldimethylsilanyloxy)ethyl)-1-(methylthio)-4-oxoazetidin-2-yl acetate, P2, has been investigated in water in the pH range 3-9 and in two (calcareous and forest) soils, then compared to amoxicillin, a β-lactam antibiotic used in human and veterinary medicine. P1 and P2 persistence in water was lower than that of amoxicillin with only a few exceptions. P1 hydrolysis was catalyzed at an acidic pH whereas P2 hydrolysis takes place at both acidic and alkaline pH values. P1 persistence in soils depended mainly on their water potential (t1/2: 35.0-70.7d at wilting point; <1d at field capacity) whereas for P2 it was shorter and unaffected by soil water content (t1/2 0.13-2.5d). Several degradation products were detected in soils at both water potentials, deriving partly from hydrolytic pathways and partly from microbial transformation. The higher LogKow value for P2 compared with P1 seemingly confers P2 with high permeability to microbial membranes regardless of soil water content. P1 and P2 persistence in soils at wilting point was shorter than that of amoxicillin, whereas it had the same extent at field capacity.

Membrane vis-LED photoreactor for simultaneous penicillin G degradation and TiO2 separation

The hybrid membrane photoreactor (MPR) combining a photoreactor irradiated with visible-light-emitting diode (vis-LED) and a cross-flow microfiltration (MF) membrane module was investigated in both closed-loop and continuous flow-through modes for the simultaneous degradation of penicillin G (PG) and separation of visible-light responsive TiO(2) particles, namely C-sensitized-N-doped TiO(2) (T300) and C-N-S tridoped TiO(2) (T0.05-450). The turbidity of permeate water was <0.2 NTU for both T300 and T0.05-450 suspensions in the MPR system operated at different transmembrane pressures (TMPs) and cross-flow velocities (CFVs), indicating effective separation of TiO(2) particles by the MF membrane. The operations at a higher TMP or lower CFV were more prone to induce TiO(2) deposition on the membrane surface without backwashing, which resulted in the membrane fouling, the loss of TiO(2) from the photoreactor and the decrease of PG photocatalytic degradation efficiency. 75% and 84% of PG were degraded in the closed-loop MPR without backwashing operated at 10 kPa and 0.15 m s(-1) after 4 h of vis-LED irradiation using 1.0 g L(-1) of T300 and T0.05-450, respectively. With backwashing of the membrane, the PG photocatalytic degradation efficiencies in the closed-loop MPR could be significantly enhanced to achieve 93% and 95% using 1.0 g L(-1) of T300 and T0.05-450, respectively, which were almost comparable to those achieved in the batch photoreactor. Due to its shorter hydraulic residence time in the photoreactor, the PG degradation efficiency in the continuous flow-through MPR with backwashing was lower than that achieved in the closed-loop MPR.

Identification of new minor metabolites of penicillin G in human serum by multiple-stage tandem mass spectrometry

Liquid chromatography/mass spectrometry (LC/MS) and liquid chromatography/tandem mass spectrometry (LC/MS/MS) were applied to characterize drug metabolites. Although these two methods have overcome the identification and structural characterization of metabolites analysis, they remain time-consuming processes. In this study, a novel multiple-stage tandem mass spectrometric method (MS(n) ) was evaluated for identification and characterization of new minor metabolism profiling of penicillin G, one of the β-lactam antibiotics, in human serum. Seven minor metabolites including five phase I metabolites and two phase II metabolites of penicillin G were identified by using data-dependent LC/MS(n) screening in one chromatographic run. The accuracy masses of seven identified metabolites of penicillin G were also confirmed by mass spectral calibration software (MassWorks™). The proposed data-dependent LC/MS(n) method is a powerful tool to provide large amounts of the necessary structural information to characterize minor metabolite in metabolism profiling.

Fate of antibiotics during municipal water recycling treatment processes

Municipal water recycling processes are potential human and environmental exposure routes for low concentrations of persistent antibiotics. While the implications of such exposure scenarios are unknown, concerns have been raised regarding the possibility that continuous discharge of antibiotics to the environment may facilitate the development or proliferation of resistant strains of bacteria. As potable and non-potable water recycling schemes are continuously developed, it is imperative to improve our understanding of the fate of antibiotics during conventional and advanced wastewater treatment processes leading to high-quality water reclamation. This review collates existing knowledge with the aim of providing new insight to the influence of a wide range of treatment processes to the ultimate fate of antibiotics during conventional and advanced wastewater treatment. Although conventional biological wastewater treatment processes are effective for the removal of some antibiotics, many have been reported to occur at 10-1000 ng L(-1) concentrations in secondary treated effluents. These include beta-lactams, sulfonamides, trimethoprim, macrolides, fluoroquinolones, and tetracyclines. Tertiary and advanced treatment processes may be required to fully manage environmental and human exposure to these contaminants in water recycling schemes. The effectiveness of a range of processes including tertiary media filtration, ozonation, chlorination, UV irradiation, activated carbon adsorption, and NF/RO filtration has been reviewed and, where possible, semi-quantitative estimations of antibiotics removals have been provided.