The fungus Pestalotiopsis guepini as a model for biotransformation of ciprofloxacin and norfloxacin

Efficiency of phytoremediation and identification of biotransformation pathways of fluoroquinolones in the aquatic environment

Phytoremediation is a low-cost and sustainable green technology that uses plants to remove organic and inorganic pollutants from aquatic environments. The aim of this study was to investigate the phytoextraction, phytoaccumulation, and phytotransformation of three fluoroquinolones (FQs) (ciprofloxacin [CIP], enrofloxacin [ENF], and levofloxacin [LVF]) by Japanese radish (Raphanus sativus var. longipinnatus) and duckweed (Lemma minor). Determination of FQs and identification of their transformation products (TPs) were performed using ultra-high-performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS). Inter-tissue translocation of FQs in Japanese radish tissues depended on their initial concentration in the medium. CIP (IT = 14.4) and ENF (IT = 17.0) accumulated mainly in radish roots, while LVF in leaves (IT = 230.8) at an initial concentration of 10 µg g-1. CIP (2,104 ng g-1) was detected in the highest concentration, followed by ENF (426.3 ng g-1) and LVF (273.3 ng g-1) in the tissues of both plants. FQs' bioaccumulation factors were significantly higher for duckweed (1.490-18.240) than Japanese radish (0.027-0.103). The removal of FQs from water using duckweed was mainly due to their photolysis and hydrolysis than plant sorption. In the screening, analysis detected 29 FQ TPs. The biotransformation pathways of FQs are described in detail, and the factors that influence their formation are indicated.

Pestalotiopsis Diversity: Species, Dispositions, Secondary Metabolites, and Bioactivities

Pestalotiopsis species have gained attention thanks to their structurally complex and biologically active secondary metabolites. In past decades, several new secondary metabolites were isolated and identified. Their bioactivities were tested, including anticancer, antifungal, antibacterial, and nematicidal activity. Since the previous review published in 2014, new secondary metabolites were isolated and identified from Pestalotiopsis species and unidentified strains. This review gathered published articles from 2014 to 2021 and focused on 239 new secondary metabolites and their bioactivities. To date, 384 Pestalotiopsis species have been discovered in diverse ecological habitats, with the majority of them unstudied. Some may contain secondary metabolites with unique bioactivities that might benefit pharmacology.

Microbial degradation of antibiotic: future possibility of mitigating antibiotic pollution

Antibiotics are the major pharmaceutical wastes that are being exposed to the environment from the pharmaceutical industries and for the anthropogenic activities. The use of antibiotics for disease prevention and treatment in humans has been surpassed by the amount used in agriculture, particularly on livestock. It is stipulated that the overuse of antibiotics is the single largest reason behind the rise of bacterial anti-microbial resistance (AMR). The development of alternative therapy, like gene therapy, immunotherapy, use of natural products, and various nanoparticles, to control bacterial pathogens might be an alternative of antibiotics for mankind but the remediation of already exposed antibiotics from the lithosphere and hydrosphere needs to be envisioned with priority. The ever-increasing release of antibiotics in the environment makes it one of the major emerging contaminants (ECs). Decomposition of such antibiotic contaminants is a great challenge to get a cleaner environment. There are reports describing the degradation of antibiotics by photolysis, hydrolysis, using cathode and metal salts, or by degradation via microbes. Antimicrobials like sulfonamides are recalcitrant to natural biodegradation, exhibiting high thermal stability. There are recent reports on microbial degradation of a few common antibiotics and their derivatives but their applications in waste management are scanty. It could however be a major concern to the scientists whether to use the antibiotic degradation traits of a microbe for the removal of antibiotic wastes. The complexity of the genetic clusters of a microbe that are responsible for degradation is crucial, as a small genetic cluster might have higher chance of horizontal transfer into sensitive species of the normal microbial flora that in turn triggers the rise of antimicrobial resistance.

Occurrence and temporal variation of antibiotics and antibiotic resistance genes in hospital inpatient department wastewater: Impacts of daily schedule of inpatients and wastewater treatment process

The temporal variation of antibiotics and ARGs as well as the impact of daily schedule of inpatients on their regular occurrence in hospital wastewater (HWW) were previously obscure. In this study, the wastewater of the inpatient department pre- and posttreatment (hydraulic retention time = 8 h) was collected intraday and intraweek. The absolute concentrations of antibiotics/metabolites and ARGs in HWW were analyzed to investigate the temporal variations of their occurrence levels. Fluoroquinolones were the predominant drugs used in the inpatient department (681.30-881.66 ng/mL in the effluent) and the main contaminant in the outlet of the disinfection pond (538.29-671.47 ng/mL). Diurnal variations peaked at 19:00 for most antibiotics and ARGs, while the maximum of them occurred on weekends. Aminoglycoside resistance genes (AMRGs, 21.6-23000 copies/mL) and β-lactam resistance genes (BLGRs, 1.24-8500 copies/mL) were the dominant ARGs before and after treatment processing, respectively (p < 0.05). The significant removal rates (>50%) of most antibiotics and ARGs, as well as the integrase gene intI1 and 16S rRNA gene, were found to be subjected solely to the chloride disinfection process, suggesting the necessity of the self-contained wastewater treatment process. Meanwhile, the statistically significant correlation among antibiotics, ARGs, intI1, and 16S rRNA (p < 0.05) demonstrated that the risk of selective pressure, horizontal transfer and vertical propagation of ARGs in the effluent of the hospital was warranted. Principal component analysis (PCA) showed that the daily schedule of inpatients and wastewater treatment processes could markedly induce fluctuations in antibiotic and ARG levels in HWW, indicating that they should be considered an impact factor for environmental monitoring. This study demonstrated for the first time the temporal variations in the abundance and dissemination of antibiotics and ARGs in a semiclosed zone and provided new insight into the development of assessments of the associated ecological risk and human health.

Biocatalytic remediation of pharmaceutically active micropollutants for environmental sustainability

The discharge of an alarming number of recalcitrant pollutants from various industrial activities presents a serious threat to environmental sustainability and ecological integrity. Bioremediation has gained immense interest around the world due to its environmentally friendly and cost-effective nature. In contrast to physical and chemical methods, the use of microbial enzymes, particularly immobilized biocatalysts, has been demonstrated as a versatile approach for the sustainable mitigation of environmental pollution. Considerable attention is now devoted to developing novel enzyme engineering approaches and state-of-the-art bioreactor design for ameliorating the overall bio-catalysis and biodegradation performance of enzymes. This review discusses the contemporary and state of the art technical and scientific progress regarding applying oxidoreductase enzyme-based biocatalytic systems to remediate a vast number of pharmaceutically active compounds from water and wastewater bodies. A comprehensive insight into enzyme immobilization, the role of mediators, bioreactors designing, and transformation products of pharmaceuticals and their associated toxicity is provided. Additional studies are necessary to elucidate enzymatic degradation mechanisms, monitor the toxicity levels of the resulting degraded metabolites and optimize the entire bio-treatment strategy for technical and economical affordability.

Effects of different carbon sources on the removal of ciprofloxacin and pollutants by activated sludge: Mechanism and biodegradation

This research investigated the effects of ciprofloxacin (CIP) (0.5, 5, and 20 mg/L) on SBR systems under different carbon source conditions. Microbial community abundance and structure were determined by quantitative PCR and high-throughput sequencing, respectively. The biodegradation production of CIP and possible degradation mechanism were also studied. Results showed that CIP had adverse effects on the nutrient removal from wastewater. Compared with sodium acetate, glucose could be more effectively used by microorganisms, thus eliminating the negative effects of CIP. Glucose stimulated the microbial abundance and increased the removal rate of CIP by 18%-24%. The mechanism research indicated that Proteobacteria and Acidobacteria had a high tolerance for CIP. With sodium acetate as a carbon source, the abundance of nitrite-oxidizing bacterial communities decreased under CIP, resulting in the accumulation of nitrite and nitrate. Rhodanobacter and Microbacterium played a major role in nitrification and denitrification when using sodium acetate and glucose as carbon sources. Dyella and Microbacterium played positive roles in the degradation process of CIP and eliminated the negative effect of CIP on SBR, which was consistent with the improved removal efficiency of pollutants.

Treatment technologies to mitigate the harmful effects of recalcitrant fluoroquinolone antibiotics on the environ- ment and human health

Antibiotic proliferation in the environment and their persistent nature is an issue of global concern as they induce antibiotic resistance threatening both human health and the ecosystem. Antibiotics have therefore been categorized as emerging pollutants. Fluoroquinolone (FQs) antibiotics are an emerging class of contaminants that are used extensively in human and veterinary medicine. The recalcitrant nature of fluoroquinolones has led to their presence in wastewater, effluents and water bodies. Even at a low concentration, FQs can stimulate antibacterial resistance. The main sources of FQ contamination include waste from pharmaceutical manufacturing industries, hospitals and households that ultimately reaches the wastewater treatment plants (WWTPs). The conventional WWTPs are unable to completely remove FQs due to their chemical stability. Therefore, the development and implementation of more efficient, economical, convenient treatment and removal technologies are needed to adequately address the issue. This review provides an overview of the technologies available for the removal of fluoroquinolone antibiotics from wastewater including adsorptive removal, advanced oxidation processes, removal using non-carbon based nanomaterials, microbial degradation and enzymatic degradation. Each treatment technology is discussed on its merits and limitations and a comparative view is presented on the choice of an advanced treatment process for future studies and implementation. A discussion on the commercialization potential and eco-friendliness of each technology is also included in the review. The importance of metabolite identification and their residual toxicity determination has been emphasized. The last section of the review provides an overview of the policy interventions and regulatory frameworks that aid in retrofitting antibiotics as a central key focus contaminant and thereby defining the discharge limits for antibiotics and establishing safe manufacturing practices.

Potential biotransformation pathways and efficiencies of ciprofloxacin and norfloxacin by an activated sludge consortium

Fluoroquinolones (FQs), such as ciprofloxacin (CIP) and norfloxacin (NOR), are types of emerging trace pollutants that have attracted great attention. In this study, an activated sludge (AS) consortium with high bio-removal capability to CIP and NOR was obtained by acclimating with CIP and NOR for 10 d. Meanwhile, a CIP- and NOR- transforming bacterial strain (S5), which is highly homologous to the 16S rRNA gene sequence of Enterobacter sp., was isolated from the acclimated AS. The bio-removal efficiency of CIP under the acclimated AS consortium was better than that under the pure culture of Enterobacter sp. S5 (93.1% vs. 89.3%), while the bio-removal efficiency of NOR under the acclimated AS consortium was lower than that under the pure culture of Enterobacter sp. S5 (83.9% vs. 89.8%). The biotransformation and bio-adsorption were two main ways to bio-remove CIP and NOR. However, the CIP and NOR biotransformation efficiencies of the acclimated AS were higher than under the pure culture of Enterobacter sp. S5, while the CIP and NOR adsorption of acclimated AS were lower than that under the pure culture of Enterobacter sp. S5. The N-acetylciprofloxacin and N-acetylnorfloxacin were the main biotransformation products of CIP and NOR. It is possible that acetyltransferase may be involved in the biotransformation process. Whether under the pure culture or AS consortium, the cytotoxicity of CIP and NOR transformation products to gram-negative bacteria was alleviated. Therefore, the acclimated AS and Enterobacter sp. S5 might provide a new strategy for removing contaminants and alleviating of FQs resistance.

Anaerobic biodegradation of levofloxacin by enriched microbial consortia: Effect of electron acceptors and carbon source

For improving the understanding of anaerobic degradation mechanism of fluoroquinolone antibiotics (FQs), the degradation of a representative FQs, levofloxacin (LEV), by six enriched anaerobic consortia were explored in this study. The effect of sulfate and nitrate as the electron acceptor and glucose as the carbon source on LEV anaerobic degradation were investigated. Addition of glucose and nitrate alone deteriorated LEV removal from 36.5% to 32.7% and 29.1%, respectively. Addition of sulfate slightly improved LEV removal to 39.6%, while simultaneous addition of glucose and sulfate significantly enhanced LEV removal to 53.1%. Twelve biodegradation intermediates were identified, which indicated that cleavage of piperazine ring is prior to that of quinolone ring, and hydroxylation, defluorination, demethylation, and decarboxylation were the primary steps of LEV anaerobic degradation. Lactobacillus, unclassified _f_Enterobacteriaceae, and Bacillus were enriched by simultaneous addition of glucose and sulfate, with relative abundance of 63.5%, 32.7%, and 3.3%, respectively. The predicted high gene abundance of xenobiotics biodegradation & metabolism, carbohydrate metabolism, and assimilatory sulfate reduction in the consortium, indicated a co-metabolism between carbohydrate metabolism, sulfate metabolism, and LEV degradation under glucose and sulfate added condition. The study revealed that simultaneous addition of glucose and sulfate is the favorable condition for LEV anaerobic degradation.

Ciprofloxacin-degrading Paraclostridium sp. isolated from sulfate-reducing bacteria-enriched sludge: Optimization and mechanism

Ciprofloxacin (CIP), one of the most widely used fluoroquinolone antibiotics, is frequently detected in the effluents of wastewater treatment plants and aquatic environments. In this study, a CIP-degrading bacterial strain was isolated from the sulfate reducing bacteria (SRB)-enriched sludge, identified as Paraclostridium sp. (i.e., strain S2). The effects of critical operational parameters on CIP removal by the strain S2 were systematically studied and these parameters were optimized via response surface methodology to maximize CIP removal. Furthermore, the pathway and kinetics of CIP removal were investigated by varying the initial CIP concentrations (from 0.1 to 20 mg/L). The CIP removal was characterized by rapid sorption followed by biotransformation with a specific biotransformation rate of 1975.7 ± 109.1 µg/g-cell dry weight/h at an initial CIP concentration of 20 mg/L. Based on the main transformation products, several biotransformation pathways have been proposed including piperazine ring cleavage, OH/F substitution, decarboxylation, and hydroxylation as the major transformation reactions catalyzed by cytochrome P450 and dehydrogenases. Acute toxicity assessment apparently shows that CIP biotransformation by strain S2 resulted in the formation of less toxic intermediates. To the best of our knowledge, this is the very first study in which a key functional microbe, Paraclostridium sp., highly effective in CIP biotransformation, was isolated from SRB-enriched sludge. The findings of this study could facilitate in developing appropriate bioaugmentation strategy, and in designing and operating an SRB-based engineered process for treating CIP-laden wastewater.

Biodegradation of fluoroquinolone antibiotics and the climbazole fungicide by Trichoderma species

Filamentous fungi Trichoderma have been able to efficiently degrade fluoroquinolone antibiotics namely ciprofloxacin (CIP) and ofloxacin (OFL) as well as the fungicide climbazole (CLB) that are persistent in conventional activated sludge processes. All targeted compounds were biotransformed by whole cells of Trichoderma spp., exactly T. harzanium and T. asperellum, and biosorption played a limited role in their elimination. However, contrasting results were obtained with the two strains. T. asperellum was more efficient against CIP, with a 81% degradation rate in 13 days of incubation, while T. harzianum was more efficient against CLB, with a 91% degradation rate. While in the case of OFL, both strains showed same efficiency with degradation rate around 40%. Adding a cytochrome P450 enzyme inhibitor hardly resulted in the modification of degradation kinetics supporting the implication of extracellular enzymes in chemical biotransformation. Transformation products were identified by liquid chromatography-high resolution-mass spectrometry and transformation pathways were proposed. Biotransformation of selected compounds included hydroxylation, oxidation/reduction and N- and O-dealkylation reactions, similarly to those reported with white rot fungi. CIP underwent transformations at the piperazinyl ring through oxidation and conjugation reactions, while OFL mainly underwent hydroxylation processes and CLB carbonyl reduction into alcohol. Consequently, Trichoderma spp. likely possess a machinery of unspecific enzymes, which makes their application in removal of pharmaceutical and personal care products attractive.

Biotransformation of ciprofloxacin by Xylaria longipes: structure elucidation and residual antibacterial activity of metabolites

The impressive ability of the fungus Xylaria longipes to transform the highly persistent fluoroquinolone ciprofloxacin into microbiologically less active degradation products was demonstrated. Fluoroquinolones are used extensively in both human and veterinary medicine. Poor metabolization and high chemical stability of these synthetic antibiotics led to their presence in several environmental compartments. This undesirable behavior may promote the spread of resistance mechanisms due to concomitant exposure to bacteria. Therefore, the biotransformation of ciprofloxacin, one of the most prescribed fluoroquinolones in human medicine, by the ascomycetous soft rot fungus X. longipes was investigated in detail. Submerged cultivation of the fungus allowed for high-yield formation of four biotransformation products. These compounds were subsequently purified by preparative high-performance liquid chromatography. Applying accurate mass spectrometry and nuclear magnetic resonance spectroscopy, desethylene-ciprofloxacin, desethylene-N-acetyl-ciprofloxacin, N-formyl-ciprofloxacin and N-acetyl-ciprofloxacin were unambiguously identified. N-acetylation and N-formylation of the drug led to a 75-88% reduction of the initial antibacterial activity, whereas a breakdown of the piperazine substituent resulted in almost inactive products. These findings suggest an important role in the inactivation and degradation of this and other synthetic compounds in the environment.

Ciprofloxacin degradation in anaerobic sulfate-reducing bacteria (SRB) sludge system: Mechanism and pathways

Ciprofloxacin (CIP), a fluoroquinolone antibiotic, removal was examined for the first time, in an anaerobic sulfate-reducing bacteria (SRB) sludge system. About 28.0% of CIP was biodegraded by SRB sludge when the influent CIP concentration was 5000 μg/L. Some SRB genera with high tolerance to CIP (i.e. Desulfobacter), were enriched at CIP concentration of 5000 μg/L. The changes in antibiotic resistance genes (ARGs) of SRB sludge coupled with CIP biodegradation intermediates were used to understand the mechanism of CIP biodegradation for the first time. The percentage of efflux pump genes associated with ARGs increased, while the percentage of fluoroquinolone resistance genes that inhibit the DNA copy of bacteria decreased during prolonged exposure to CIP. It implies that some intracellular CIP was extruded into extracellular environment of microbial cells via efflux pump genes to reduce fluoroquinolone resistance genes accumulation caused by exposure to CIP. Additionally, the degradation products and the possible pathways of CIP biodegradation were also examined using the new method developed in this study. The results suggest that CIP was biodegraded intracellularly via desethylation reaction in piperazinyl ring and hydroxylation reaction catalyzed by cytochrome P450 enzymes. This study provides an insight into the mechanism and pathways of CIP biodegradation by SRB sludge, and opens-up a new opportunity for the treatment of CIP-containing wastewater using sulfur-mediated biological process.

Removal of pharmaceutical compounds in water and wastewater using fungal oxidoreductase enzymes

Due to recalcitrance of some pharmaceutically active compounds (PhACs), conventional wastewater treatment is not able to remove them effectively. Therefore, their occurrence in surface water and potential environmental impact has raised serious global concern. Biological transformation of these contaminants using white-rot fungi (WRF) and their oxidoreductase enzymes has been proposed as a low cost and environmentally friendly solution for water treatment. The removal performance of PhACs by a fungal culture is dependent on several factors, such as fungal species, the secreted enzymes, molecular structure of target compounds, culture medium composition, etc. In recent 20 years, numerous researchers tried to elucidate the removal mechanisms and the effects of important operational parameters such as temperature and pH on the enzymatic treatment of PhACs. This review summarizes and analyzes the studies performed on PhACs removal from spiked pure water and real wastewaters using oxidoreductase enzymes and the data related to degradation efficiencies of the most studied compounds. The review also offers an insight into enzymes immobilization, fungal reactors, mediators, degradation mechanisms and transformation products (TPs) of PhACs. In brief, higher hydrophobicity and having electron-donating groups, such as amine and hydroxyl in molecular structure leads to more effective degradation of PhACs by fungal cultures. For recalcitrant compounds, using redox mediators, such as syringaldehyde increases the degradation efficiency, however they may cause toxicity in the effluent and deactivate the enzyme. Immobilization of enzymes on supports can enhance the performance of enzyme in terms of reusability and stability. However, the immobilization strategy should be carefully selected to reduce the cost and enable regeneration. Still, further studies are needed to elucidate the mechanisms involved in enzymatic degradation and the toxicity levels of TPs and also to optimize the whole treatment strategy to have economical and technical competitiveness.

Biotransformation of 4-fluoro-N-(1-{2-[(propan-2-yl)phenoxy]ethyl}-8-azabicyclo[3.2.1]octan-3-yl)-benzenesulfonamide, a novel potent 5-HT7 receptor antagonist with antidepressant-like and anxiolytic properties: In vitro and in silico approach

The aim of the study was to investigate the metabolism of 4-fluoro-N-(1-{2-[(propan-2-yl)phenoxy]ethyl}-8-azabicyclo[3.2.1]octan-3-yl)-benzenesulfonamide (PZ-1150), a novel 5-HT₇ receptor antagonist with antidepressant-like and anxiolytic properties, by the following three ways: in vitro with microsomes; in vitro employing Cunninghamella echinulata, and in silico using MetaSite. Biotransformation of PZ-1150 with microsomes resulted in five metabolites, while transformation with C. echinulata afforded two metabolites. In both models, the predominant metabolite occurred due to hydroxylation of benzene ring. In silico data coincide with in vitro experiments, as three MetaSite metabolites matched compounds identified in microsomal samples. In human liver microsomes PZ-1150 exhibited in vitro half-life of 64 min, with microsomal intrinsic clearance of 54.1 μL/min/mg and intrinsic clearance of 48.7 mL/min/kg. Therefore, PZ-1150 is predicted to be a high-clearance agent. The study demonstrated the applicability of using microsomal model coupled with microbial model to elucidate the metabolic pathways of compounds and comparison with in silico metabolite predictions.

Application and evaluation of a high-resolution mass spectrometry screening method for veterinary drug residues in incurred fish and imported aquaculture samples

The ability to detect chemical contaminants, including veterinary drug residues in animal products such as fish, is an important example of food safety analysis. In this paper, a liquid chromatography high-resolution mass spectrometry (LC-HRMS) screening method using a quadrupole-Orbitrap instrument was applied to the analysis of veterinary drug residues in incurred tissues from aquacultured channel catfish, rainbow trout, and Atlantic salmon and imported aquacultured products including European eel, yellow croaker, and tilapia. Compared to traditional MS methods, the use of HRMS with nontargeted data acquisition and exact mass measurement capability greatly increased the scope of compounds that could be monitored simultaneously. The fish samples were prepared for analysis using a simple efficient procedure that consisted of an acidic acetonitrile extraction followed by solid phase extraction cleanup. Two different HRMS acquisition programs were used to analyze the fish extracts. This method detected and identified veterinary drugs including quinolones, fluoroquinolones, avermectins, dyes, and aminopenicillins at residue levels in fish that had been dosed with those compounds. A metabolite of amoxicillin, amoxicillin diketone, was also found at high levels in catfish, trout, and salmon. The method was also used to characterize drug residues in imported fish. In addition to confirming findings of fluoroquinolone and sulfonamide residues that were found by traditional targeted MS methods, several new compounds including 2-amino mebendazole in eel and ofloxacin in croaker were detected and identified. Graphical Abstract Aquacultured samples are analyzed with a high-resolution mass spectrometry screening method to detect and identify unusual veterinary drug residues including ofloxacin in an imported fish.

Study of ciprofloxacin biodegradation by a Thermus sp. isolated from pharmaceutical sludge

Ciprofloxacin (CIP) is an antibiotic drug frequently detected in manure compost and is difficult to decompose at high temperatures, resulting in a potential threat to the environment. Microbial degradation is an effective and environmentally friendly method to degrade CIP. In this study, a thermophilic bacterium that can degrade CIP was isolated from sludge sampled from an antibiotics pharmaceutical factory. This strain is closely related to Thermus thermophilus based on 16S rRNA gene sequence analysis and is designated C419. The optimal temperature and pH values for CIP degradation are 70°C and 6.5, respectively, and an appropriate sodium acetate concentration promotes CIP degradation. Seven major biodegradation metabolites were identified by an ultra-performance liquid chromatography tandem mass spectrometry analysis. In addition, strain C419 degraded other fluoroquinolones, including ofloxacin, norfloxacin and enrofloxacin. The supernatant from the C419 culture grown in fluoroquinolone-containing media showed attenuated antibacterial activity. These results indicate that strain C419 might be a new auxiliary bacterial resource for the biodegradation of fluoroquinolone residue in thermal environments.

Rapid detection of AAC(6')-Ib-cr production using a MALDI-TOF MS strategy

Plasmid-mediated quinolone resistance mechanisms have become increasingly prevalent among Enterobacteriaceae strains since the 1990s. Among these mechanisms, AAC(6')-Ib-cr is the most difficult to detect. Different detection methods have been developed, but they require expensive procedures such as Sanger sequencing, pyrosequencing, polymerase chain reaction (PCR) restriction, or the time-consuming phenotypic method of Wachino. In this study, we describe a simple matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) method which can be easily implemented in clinical laboratories that use the MALDI-TOF technique for bacterial identification. We tested 113 strains of Enterobacteriaceae, of which 64 harbored the aac(6')-Ib-cr gene. We compared two MALDI-TOF strategies, which differed by their norfloxacin concentration (0.03 vs. 0.5 g/L), and the method of Wachino with the PCR and sequencing strategy used as the reference. The MALDI-TOF strategy, performed with 0.03 g/L norfloxacin, and the method of Wachino yielded the same high performances (Se = 98 %, Sp = 100 %), but the turnaround time of the MALDI-TOF strategy was faster (<5 h), simpler, and inexpensive (<1 Euro). Our study shows that the MALDI-TOF strategy has the potential to become a major method for the detection of many different enzymatic resistance mechanisms.

Microbial degradation of fluorinated drugs: biochemical pathways, impacts on the environment and potential applications

Since the discovery over 60 years ago of fluorocortisone's biological properties (9-α-Fluoro derivatives of cortisone and hydrocortisone; Fried J and Sabo EF, J Am Chem Soc 76: 1455-1456, 1954), the number of fluorinated drugs has steadily increased. With the improvement in synthetic methodologies, this trend is likely to continue and will lead to the introduction of new fluorinated substituents into pharmaceutical compounds. Although the biotransformation of organofluorine compounds by microorganisms has been well studied, specific investigations on fluorinated drugs are relatively few, despite the increase in the number and variety of fluorinated drugs that are available. The strength of the carbon-fluorine bond conveys stability to fluorinated drugs; thus, they are likely to be recalcitrant in the environment or may be partially metabolized to a more toxic metabolite. This review examines the research done on microbial biotransformation and biodegradation of fluorinated drugs and highlights the importance of understanding how microorganisms interact with this class of compound from environmental, clinical and biotechnological perspectives.

Using robust Bayesian network to estimate the residuals of fluoroquinolone antibiotic in soil

Prediction of antibiotic pollution and its consequences is difficult, due to the uncertainties and complexities associated with multiple related factors. This article employed domain knowledge and spatial data to construct a Bayesian network (BN) model to assess fluoroquinolone antibiotic (FQs) pollution in the soil of an intensive vegetable cultivation area. The results show: (1) The relationships between FQs pollution and contributory factors: Three factors (cultivation methods, crop rotations, and chicken manure types) were consistently identified as predictors in the topological structures of three FQs, indicating their importance in FQs pollution; deduced with domain knowledge, the cultivation methods are determined by the crop rotations, which require different nutrients (derived from the manure) according to different plant biomass. (2) The performance of BN model: The integrative robust Bayesian network model achieved the highest detection probability (pd) of high-risk and receiver operating characteristic (ROC) area, since it incorporates domain knowledge and model uncertainty. Our encouraging findings have implications for the use of BN as a robust approach to assessment of FQs pollution and for informing decisions on appropriate remedial measures.

Synthesis of ciprofloxacin-conjugated poly (L-lactic acid) polymer for nanofiber fabrication and antibacterial evaluation

Ciprofloxacin was conjugated with polylactide (PLA) via the secondary amine group of the piperazine ring using PLA and 7-(4-(2-Chloroacetyl) piperazin-1-yl)-1-cyclopropyl-6-fluoro-1, 4-dihydro-4-oxoquinoline-3-carboxylic acid. Zinc prolinate, a biocompatible catalyst was synthesized, characterized, and used in ring opening polymerization of L-lactide. Five different kinds of OH-terminated poly(L-lactide) (two-, three-, four-, six-arm, star-shaped) homopolymers were synthesized by ring opening polymerization of L-lactide in the presence of dodecanol, glycerol, pentaerythritol, dipentaerythritol as initiator and zinc prolinate as a catalyst. The structures of the polymers and conjugates were thoroughly characterized by means of gel permeation chromatography, matrix-assisted laser desorption/ionization – time of flight mass spectrometry, and nuclear magnetic resonance spectroscopy. PLA (molecular weight =100,000) and ciprofloxacin conjugated PLA were used for fabrication of nonwoven nanofiber mat (diameter ranges; 150–400 nm) having pore size (62–102 nm) using electrospinning. The microbiological assessment shows that the release of ciprofloxacin possesses antimicrobial activity. The drug-release behavior of the mat was studied to reveal potential application as a drug delivery system. The result shows that the ciprofloxacin release rates of the PLA conjugate nonwoven nanofiber mat could be controlled by the drug loading content and the release medium. The development of a biodegradable ciprofloxacin system, based on nonwoven nanofiber mat, should be of great interest in drug delivery systems.

Adsorption, inhibition, and biotransformation of ciprofloxacin under aerobic conditions

The adsorption, inhibition, and biotransformation of the fluoroquinolone antibiotic ciprofloxacin (CIP) under aerobic conditions were investigated in this study. The maximum adsorption capacity and the Langmuir constant were 37.9 mg CIP/g VSS and 37 L/g, respectively. A glucose-fed aerobic culture was inhibited by CIP at 10mg/L or higher and the degree of inhibition increased with increasing CIP concentration. However, the microbial activity recovered to some extent with prolonged incubation under a semi-continuous feeding mode. A low extent of CIP biotransformation was observed in an aerobic, glucose-fed culture derived from poultry litter extract. LC/UV/MS analysis of the biotransformation product showed that only the piperazine ring was oxidized, while the antibiotic quinolone part of CIP was intact.

Occurrence of chloramphenicol-resistance genes as environmental pollutants from swine feedlots

Chloramphenicol-resistance genes could be propagated to the surrounding environment via agricultural application of swine waste. This study investigated the potential risks of chloramphenicol-resistance genes from swine feedlots and their surrounding environment. We applied a culture-independent method to investigate levels of chloramphenicol-resistance genes in the wastewater from swine feedlots and the correspondingly impacted agricultural fields in Beijing. The cmlA, floR, fexA, cfr, and fexB genes were present in all samples, with the highest absolute concentrations of 1.50 × 10(6) copies/g in soil and 6.69 × 10(6) copies/mL in wastewater. The concentration of chloramphenicol residue was determined by ultra performance liquid chromatography-electrospray tandem mass spectrometry (UPLC-MS/MS), with the highest concentrations of 0.83 ng/g in soil and 11.5 ng/mL in wastewater. Significant correlations were found between chloramphenicol-resistance genes and chloramphenicol residues (r = 0.79, p = 0.0008) as well as between chloramphenicol-resistance genes in swine feedlots and corresponding agricultural soils (r = 0.84, p = 0.02). Consequently, swine feedlot wastewater could become a source of chloramphenicol-resistance genes, which could then lead to the spread of antibiotic resistance and eventually pose a risk to public health. To our knowledge, this is the first study to examine the occurrence of floR, fexA, cfr, and fexB genes in the environment using a culture-independent method.

Microbial transformations of antimicrobial quinolones and related drugs

The quinolones are an important group of synthetic antimicrobial drugs used for treating bacterial diseases of humans and animals. Microorganisms transform antimicrobial quinolones (including fluoroquinolones) and the pharmacologically related naphthyridones, pyranoacridones, and cinnolones to a variety of metabolites. The biotransformation processes involve hydroxylation of methyl groups; hydroxylation of aliphatic and aromatic rings; oxidation of alcohols and amines; reduction of carboxyl groups; removal of methyl, carboxyl, fluoro, and cyano groups; addition of formyl, acetyl, nitrosyl, and cyclopentenone groups; and cleavage of aliphatic and aromatic rings. Most of these reactions greatly reduce or eliminate the antimicrobial activity of the quinolones.

Degradation of the antibiotics norfloxacin and ciprofloxacin by a white-rot fungus and identification of degradation products

More than 90% of the antibiotics ciprofloxacin (CIPRO) and norfloxacin (NOR) at 2 mg L(-1) were degraded by Trametes versicolor after 7 days of incubation in malt extract liquid medium. In in vitro assays with purified laccase (16.7 nkat mL(-1)), an extracellular enzyme excreted constitutively by this fungus, 16% of CIPRO was removed after 20 h. The addition of the laccase mediator 2,2-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt led to 97.7% and 33.7% degradation of CIPRO and NOR, respectively. Inhibition of CIPRO and NOR degradation by the cytochrome P450 inhibitor 1-aminobenzotriazole suggests that the P450 system also plays a role in the degradation of the two antibiotics. Transformation products of CIPRO and NOR were monitored at different incubation times by triple-quadrupole and quadrupole time-of-flight mass spectrometry, and can be assigned to three different reaction pathways: (i) oxidation of the piperazinyl substituent, (ii) monohydroxylation, and (iii) formation of dimeric products.

Modification of norfloxacin by a Microbacterium sp. strain isolated from a wastewater treatment plant

Antimicrobial residues found in municipal wastewater may increase selective pressure on microorganisms for development of resistance, but studies with mixed microbial cultures derived from wastewater have suggested that some bacteria are able to inactivate fluoroquinolones. Medium containing N-phenylpiperazine and inoculated with wastewater was used to enrich fluoroquinolone-modifying bacteria. One bacterial strain isolated from an enrichment culture was identified by 16S rRNA gene sequence analysis as a Microbacterium sp. similar to a plant growth-promoting bacterium, Microbacterium azadirachtae (99.70%), and a nematode pathogen, "M. nematophilum" (99.02%). During growth in medium with norfloxacin, this strain produced four metabolites, which were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and nuclear magnetic resonance (NMR) analyses as 8-hydroxynorfloxacin, 6-defluoro-6-hydroxynorfloxacin, desethylene norfloxacin, and N-acetylnorfloxacin. The production of the first three metabolites was enhanced by ascorbic acid and nitrate, but it was inhibited by phosphate, amino acids, mannitol, formate, and thiourea. In contrast, N-acetylnorfloxacin was most abundant in cultures supplemented with amino acids. This is the first report of defluorination and hydroxylation of a fluoroquinolone by an isolated bacterial strain. The results suggest that some bacteria may degrade fluoroquinolones in wastewater to metabolites with less antibacterial activity that could be subject to further degradation by other microorganisms.

Aquatic photochemistry of fluoroquinolone antibiotics: kinetics, pathways, and multivariate effects of main water constituents

The ubiquity of fluoroquinolone antibiotics (FQs) in surface waters urges insights into their fate in the aqueous euphotic zone. In this study, eight FQs (ciprofloxacin, danofloxacin, levofloxacin, sarafloxacin, difloxacin, enrofloxacin, gatifloxacin, and balofloxacin) were exposed to simulated sunlight, and their photodegradation was observed to follow apparent first-order kinetics. Based on the determined photolytic quantum yields, solar photodegradation half-lives for the FQs in pure water and at 45 degrees N latitude were calculated to range from 1.25 min for enrofloxacin to 58.0 min for balofloxacin, suggesting that FQs would intrinsically photodegrade fast in sunlit surface waters. However, we found freshwater and seawater constituents inhibited their photodegradation. The inhibition was further explored by a central composite design using sarafloxacin and gatifloxacin as representatives. Humic acids (HA), Fe(III), NO(3)(-), and HA-Cl(-) interaction inhibited the photodegradation, as they mainly acted as radiation filters and/or scavengers for reactive oxygen species. The photodegradation product identification and ROS scavenging experiments indicated that the FQs underwent both direct photolysis and self-sensitized photo-oxidation via *OH and (1)O(2). Piperazinyl N(4)-dealkylation was primary for N(4)-alkylated FQs, whereas decarboxylation and defluorination were comparatively important for the other FQs. These results are of importance toward the goal of assessing the persistence of FQs in surface waters.

Acetylation of fluoroquinolone antimicrobial agents by an Escherichia coli strain isolated from a municipal wastewater treatment plant

AIMS

To isolate environmental bacteria capable of transforming fluoroquinolones to inactive molecules.

METHODS AND RESULTS

Bacteria were isolated from the aerobic liquor of a wastewater treatment plant on a medium containing norfloxacin (100 mg l(-1)). Twenty-two isolates were highly resistant (minimal inhibitory concentration: 6.25-200 microg ml(-1)) to five fluoroquinolones and six of them were positive by PCR amplification for the aminoglycoside resistance gene aac(6')-Ib. Of these, only Escherichia coli strain LR09 had the ciprofloxacin-acetylating variant gene aac(6')-Ib-cr; HPLC and mass spectrometry showed that this strain transformed both ciprofloxacin and norfloxacin by N-acetylation. This bacterium also had mutations in the quinolone-resistance determining regions of the gyrA and parC genes.

CONCLUSIONS

An E. coli isolate from wastewater, which possessed at least two distinct fluoroquinolone resistance mechanisms, inactivated ciprofloxacin and norfloxacin by N-acetylation.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report of N-acetylation of fluoroquinolones by an aac(6')-Ib-cr-containing bacterium from an environmental source.

Plasmid-mediated quinolone resistance: a multifaceted threat

Although plasmid-mediated quinolone resistance (PMQR) was thought not to exist before its discovery in 1998, the past decade has seen an explosion of research characterizing this phenomenon. The best-described form of PMQR is determined by the qnr group of genes. These genes, likely originating in aquatic organisms, code for pentapeptide repeat proteins. These proteins reduce susceptibility to quinolones by protecting the complex of DNA and DNA gyrase or topoisomerase IV enzymes from the inhibitory effect of quinolones. Two additional PMQR mechanisms were recently described. aac(6')-Ib-cr encodes a variant aminoglycoside acetyltransferase with two amino acid alterations allowing it to inactivate ciprofloxacin through the acetylation of its piperazinyl substituent. oqxAB and qepA encode efflux pumps that extrude quinolones. All of these genes determine relatively small increases in the MICs of quinolones, but these changes are sufficient to facilitate the selection of mutants with higher levels of resistance. The contribution of these genes to the emergence of quinolone resistance is being actively investigated. Several factors suggest their importance in this process, including their increasing ubiquity, their association with other resistance elements, and their emergence simultaneous with the expansion of clinical quinolone resistance. Of concern, these genes are not yet being taken into account in resistance screening by clinical microbiology laboratories.

In vitro residual anti-bacterial activity of difloxacin, sarafloxacin and their photoproducts after photolysis in water

Fluoroquinolones like difloxacin (DIF) and sarafloxacin (SARA) are adsorbed in soil and enter the aquatic environment wherein they are subjected to photolytic degradation. To evaluate the fate of DIF and SARA, their photolysis was performed in water under stimulated natural sunlight conditions. DIF primarily degrades to SARA. On prolonged photodegradation, seven photoproducts were elucidated by HR-LC-MS/MS, three of which were entirely novel. The residual anti-bacterial activities of DIF, SARA and their photoproducts were studied against a group of pathogenic strains. DIF and SARA revealed potency against both gram-positive and -negative bacteria. The photoproducts also exhibited varying degrees of efficacies against the tested bacteria. Even without isolating the individual photoproducts, their impact on the aquatic environment could be assessed. Therefore, the present results call for prudence in estimating the fate of these compounds in water and in avoiding emergence of resistance in bacteria caused by the photoproducts of DIF and SARA.

Metabolism of fluoroorganic compounds in microorganisms: impacts for the environment and the production of fine chemicals

Incorporation of fluorine into an organic compound can favourably alter its physicochemical properties with respect to biological activity, stability and lipophilicity. Accordingly, this element is found in many pharmaceutical and industrial chemicals. Organofluorine compounds are accepted as substrates by many enzymes, and the interactions of microorganisms with these compounds are of relevance to the environment and the fine chemicals industry. On the one hand, the microbial transformation of organofluorines can lead to the generation of toxic compounds that are of environmental concern, yet similar biotransformations can yield difficult-to-synthesise products and intermediates, in particular derivatives of biologically active secondary metabolites. In this paper, we review the historical and recent developments of organofluorine biotransformation in microorganisms and highlight the possibility of using microbes as models of fluorinated drug metabolism in mammals.

Transformation of N -Phenylpiperazine by Mixed Cultures from a Municipal Wastewater Treatment Plant

Samples from a wastewater treatment plant were used as inocula for mixed cultures dosed with N -phenylpiperazine (NPP), a model compound containing the piperazine ring found in many fluoroquinolones. Chemical analyses showed that NPP (50 mg liter −1 ) disappeared in 12 days, with the appearance of a transient metabolite and two nitrosated compounds.