Adaptive laboratory evolution and independent component analysis disentangle complex vancomycin adaptation trajectories.

Human infections with methicillin-resistant Staphylococcus aureus (MRSA) are commonly treated with vancomycin, and strains with decreased susceptibility, designated as vancomycin-intermediate S. aureus (VISA), are associated with treatment failure. Here, we profiled the phenotypic, mutational, and transcriptional landscape of 10 VISA strains adapted by laboratory evolution from one common MRSA ancestor, the USA300 strain JE2. Using functional and independent component analysis, we found that: 1) despite the common genetic background and environmental conditions, the mutational landscape diverged between evolved strains and included mutations previously associated with vancomycin resistance (in vraT, graS, vraFG, walKR, and rpoBCD) as well as novel adaptive mutations (SAUSA300_RS04225, ssaA, pitAR, and sagB); 2) the first wave of mutations affected transcriptional regulators and the second affected genes involved in membrane biosynthesis; 3) expression profiles were predominantly strain-specific except for sceD and lukG, which were the only two genes significantly differentially expressed in all clones; 4) three independent virulence systems (φSa3, SaeR, and T7SS) featured as the most transcriptionally perturbed gene sets across clones; 5) there was a striking variation in oxacillin susceptibility across the evolved lineages (from a 10-fold increase to a 63-fold decrease) that also arose in clinical MRSA isolates exposed to vancomycin and correlated with susceptibility to teichoic acid inhibitors; and 6) constitutive expression of the VraR regulon explained cross-susceptibility, while mutations in walK were associated with cross-resistance. Our results show that adaptation to vancomycin involves a surprising breadth of mutational and transcriptional pathways that affect antibiotic susceptibility and possibly the clinical outcome of infections.

Novel N-Substituted 3-Aryl-4-(diethoxyphosphoryl)azetidin-2-ones as Antibiotic Enhancers and Antiviral Agents in Search for a Successful Treatment of Complex Infections.

A novel series of N-substituted cis- and trans-3-aryl-4-(diethoxyphosphoryl)azetidin-2-ones were synthesized by the Kinugasa reaction of N-methyl- or N-benzyl-(diethyoxyphosphoryl)nitrone and selected aryl alkynes. Stereochemistry of diastereoisomeric adducts was established based on vicinal H3-H4 coupling constants in azetidin-2-one ring. All the obtained azetidin-2-ones were evaluated for the antiviral activity against a broad range of DNA and RNA viruses. Azetidin-2-one trans-11f showed moderate inhibitory activity against human coronavirus (229E) with EC50 = 45 µM. The other isomer cis-11f was active against influenza A virus H1N1 subtype (EC50 = 12 µM by visual CPE score; EC50 = 8.3 µM by TMS score; MCC > 100 µM, CC50 = 39.9 µM). Several azetidin-2-ones 10 and 11 were tested for their cytostatic activity toward nine cancerous cell lines and several of them appeared slightly active for Capan-1, Hap1 and HCT-116 cells values of IC50 in the range 14.5-97.9 µM. Compound trans-11f was identified as adjuvant of oxacillin with significant ability to enhance the efficacy of this antibiotic toward the highly resistant S. aureus strain HEMSA 5. Docking and molecular dynamics simulations showed that enantiomer (3R,4S)-11f can be responsible for the promising activity due to the potency in displacing oxacillin at ß-lactamase, thus protecting the antibiotic from undesirable biotransformation.

Characterization of the First OXA-10 Natural Variant with Increased Carbapenemase Activity.

While carbapenem resistance in Gram-negative bacteria is mainly due to the production of efficient carbapenemases, ß-lactamases with a narrower spectrum may also contribute to resistance when combined with additional mechanisms. OXA-10-type class D ß-lactamases, previously shown to be weak carbapenemases, could represent such a case. In this study, two novel OXA-10 variants were identified as the sole carbapenem-hydrolyzing enzymes in meropenem-resistant enterobacteria isolated from hospital wastewater and found by next-generation sequencing to express additional ß-lactam resistance mechanisms. The new variants, OXA-655 and OXA-656, were carried by two related IncQ1 broad-host-range plasmids. Compared to the sequence of OXA-10, they both harbored a Thr26Met substitution, with OXA-655 also bearing a leucine instead of a valine in position 117 of the SAV catalytic motif. Susceptibility profiling of laboratory strains replicating the natural blaOXA plasmids and of recombinant clones expressing OXA-10 and the novel variants in an isogenic background indicated that OXA-655 is a more efficient carbapenemase. The carbapenemase activity of OXA-655 is due to the Val117Leu substitution, as shown by steady-state kinetic experiments, where the kcat of meropenem hydrolysis was increased 4-fold. In contrast, OXA-655 had no activity toward oxyimino-ß-lactams, while its catalytic efficiency against oxacillin was significantly reduced. Moreover, the Val117Leu variant was more efficient against temocillin and cefoxitin. Molecular dynamics indicated that Val117Leu affects the position 117-Leu155 interaction, leading to structural shifts in the active site that may alter carbapenem alignment. The evolutionary potential of OXA-10 enzymes toward carbapenem hydrolysis combined with their spread by promiscuous plasmids indicates that they may pose a future clinical threat.

Effects of Microplate Type and Broth Additives on Microdilution MIC Susceptibility Assays.

The determination of antibiotic potency against bacterial strains by assessment of their minimum inhibitory concentration normally uses a standardized broth microdilution assay procedure developed more than 50 years ago. However, certain antibiotics require modified assay conditions in order to observe optimal activity. For example, daptomycin requires medium supplemented with Ca2+, and the lipoglycopeptides dalbavancin and oritavancin require Tween 80 to be added to the growth medium to prevent the depletion of free drug via adsorption to the plastic microplate. In this report, we examine systematically the effects of several different plate types on microdilution broth MIC values for a set of antibiotics against Gram-positive and Gram-negative bacteria, both in medium alone and in medium supplemented with the commonly used additives Tween 80, lysed horse blood, and 50% human serum. We observed very significant differences in measured MICs (up to 100-fold) for some lipophilic antibiotics, such as the Gram-positive lipoglycopeptide dalbavancin and the Gram-negative lipopeptide polymyxins, and found that nonspecific binding plates can replace the need for surfactant additives. Microtiter plate types and any additives should be specified when reporting broth dilution MIC values, as results can vary dramatically for some classes of antibiotics.

Ultrafast Parallelized Microfluidic Platform for Antimicrobial Susceptibility Testing of Gram Positive and Negative Bacteria.

Antimicrobial susceptibility testing (AST) is an essential diagnostic procedure to determine the correct course of treatment for various types of pathogen infections. Patients are treated with broad spectrum antibiotics until AST results become available, which has contributed to the emergence of multidrug resistant bacteria worldwide. Conventional AST methods require 16-24 h to assess sensitivity of the bacteria to a given drug and establish its minimum inhibitory concentration (MIC). A rapid AST assay can assist clinicians in making an informed choice of targeted therapy and avoid unnecessary overprescription. Here, we have developed a highly parallelized droplet microfluidic platform that can screen four antibiotics/pathogens simultaneously and assess antibiotic sensitivity in 15-30 min. The device consists of four integrated microdroplet arrays, each hosting over 8000 docking sites, which can be operated individually or jointly for greater flexibility of operation. Small numbers (1-4) of bacterial cells were entrapped in droplets of 110 pL volume and monitored dynamically over 2 h. This imaging-based AST approach was used to determine the growth rates of four types of clinically relevant bacteria known to cause urinary tract infection (UTI) in millions of patients. We quantified doubling times of both Gram positive ( Staphylococcus aureus, Enterococcus faecalis) and Gram negative bacteria (e.g., Escherichia coli, Klebsiella pneumoniae) with varying levels of antibiotic resistance. Six concentrations of bactericidal and bacteriostatic antibiotics (oxacillin and tetracycline, respectively) were tested to determine the MIC of the strains as well as the heterogeneity in growth profiles of bacteria at single cell resolution. The MIC determined from phenotypic analysis in droplets matched the MIC obtained from broth microdilution method for all strains. The advantages of the proposed droplet-based AST, including rapid drug sensitivity response, morphological analysis, and heterogeneity in antibiotic-resistance profiles, make it an excellent alternative to standard phenotypic AST with potential applications in clinical diagnostics and point of care testing.

Radical-scavenging activity of penicillin G, ampicillin, oxacillin, and dicloxacillin.

The aim of this study was to characterize the antioxidant activity of penicillin G (PG), ampicillin (AMP), oxacillin (OX) and dicloxacillin (DOX) through their reactivity towards reactive oxygen species (superoxide anion radical, O2•̅; hydroxyl radical, HO• ; peroxyl radical, ROO• ; hydrogen peroxide, H2 O2 ; DPPH• ) using various in vitro antioxidant assays with chemiluminescence (CL) and spectrophotometry as measurement techniques. In hydroxyl radical assays , PG, OX and AMP were found to inhibit the CL signal arising from the Fenton-like reaction in a dose-dependent manner with IC50  = 0.480 ± 0.020 mM, IC50  = 0.569 ± 0.021 mM, and IC50  = 0.630 ± 0.019 mM, respectively. The highest reactivity of PG among the tested penicillins towards the HO radical was confirmed in the deoxyribose degradation assay. In the ABAP-derived ROO radical assay, the radical-scavenging ability of the test penicillins was in the following order: AMP > PG > DOX > OX. The number of reduced DPPH radicals by the drugs tested was <1 being the biggest for PG. The weak antioxidant capacity of the test penicillins was confirmed in the trolox antioxidant capacity assay (0.075 ± 0.004; 0.093 ± 0.006; 0.123 ± 0.005; 0.126 ± 0.004) for OX, AMP, DOX, PG, respectively. Use of luminol as a CL probe for estimation of penicillin reactivity towards H2 O2 showed that only AMP was able to quench light emission; the remaining antibiotics demonstrated a strong enhancing effect. All the examined compounds showed a weak antioxidant potential when estimated using the ferric-ferrozine assay. This study is the first to report the evaluation of test penicillins as antioxidants under the same reaction conditions.

mecA Gene Dissemination Among Staphylococcal and Non-staphylococcal Isolates Shed in Surface Waters.

Aquatic ecosystems represent important vehicles for the dissemination of antibiotic resistant bacteria and antibiotic resistance genes. Of particular interest are methicillin-resistant staphylococci (MRS) harboring mecA gene that confers their resistance to ß-lactams. Therefore, in this study, water samples collected from different locations of a river impacted by surrounding facilities and domestic effluents were analyzed to learn more about the occurrence of MRS and mecA gene. Out of 290, 12 surface water isolates displayed resistance to both cefoxitin and oxacillin antibiotics. Resistant staphylococcal and non-staphylococcal isolates, identified by 16S rRNA sequencing, were found to harbor mecA gene. The phylogenetic tree of partial mecA sequences obtained from staphylococcal and non-staphylococcal isolates showed sequence similarity values of 8 %-100 %. Surface water bodies receive contaminated waters via runoff, effluents from industrial, agricultural, and municipal discharges. Therefore, surface waters are not only hot spots for mecA harboring staphylococcal isolates but also non-staphylococcal isolates and require special scientific consideration.

Development of a cationic bacterial cellulose film loaded with anionic liposomes for prolonged release of oxacillin in wound dressing applications.

Dressings should protect wounds, promote healing, absorb fluids, and maintain moisture. Bacterial cellulose is a biopolymer that stands out in biomaterials due to its high biocompatibility in several applications. In the area of dressings, it is already marketed as an alternative to traditional dressings. However, it lacks any intrinsic activity; among these, the need for antimicrobial activity in infected wounds stands out. We developed a cationic cellulose film by modifying cellulose with 1-(5-carboxypentyl)pyridin-1-ium bromide, enhancing its wettability (contact angle: 26.6°) and water retention capacity (2714.37 %). This modified film effectively retained oxacillin compared to the unmodified control. Liposomal encapsulation further prolonged oxacillin release up to 11 days. Both oxacillin-loaded films and liposomal formulations demonstrated antimicrobial activity against Staphylococcus aureus. Our findings demonstrate the potential of chemically modified cellulose as a platform for controlled anionic antibiotics and/or their formulations delivery in wound care.

Properties of a novel PBP2A protein homolog from Staphylococcus aureus strain LGA251 and its contribution to the ß-lactam-resistant phenotype.

Methicillin-resistant Staphylococcus aureus (MRSA) strains show strain-to-strain variation in resistance level, in genetic background, and also in the structure of the chromosomal cassette (SCCmec) that carries the resistance gene mecA. In contrast, strain-to-strain variation in the sequence of the mecA determinant was found to be much more limited among MRSA isolates examined so far. The first exception to this came with the recent identification of MRSA strain LGA251, which carries a new homolog of this gene together with regulatory elements mecI/mecR that also have novel, highly divergent structures. After cloning and purification in Escherichia coli, PBP2A(LGA), the protein product of the new mecA homolog, showed aberrant mobility in SDS-PAGE, structural instability and loss of activity at 37 °C, and a higher relative affinity for oxacillin as compared with cefoxitin. The mecA homolog free of its regulatory elements was cloned into a plasmid and introduced into the background of the ß-lactam-susceptible S. aureus strain COL-S. In this background, the mecA homolog expressed a high-level resistance to cefoxitin (MIC = 400 µg/ml) and a somewhat lower resistance to oxacillin (minimal inhibitory concentration = 200 µg/ml). Similar to PBP2A, the protein homolog PBP2A(LGA) was able to replace the essential function of the S. aureus PBP2 for growth. In contrast to PBP2A, PBP2A(LGA) did not depend on the transglycosylase activity of the native PBP2 for expression of high level resistance to oxacillin, suggesting that the PBP2A homolog may preferentially cooperate with a monofunctional transglycosylase as the alternative source of transglycosylase activity.

Pyridylpiperazine-based allosteric inhibitors of RND-type multidrug efflux pumps.

Efflux transporters of the RND family confer resistance to multiple antibiotics in Gram-negative bacteria. Here, we identify and chemically optimize pyridylpiperazine-based compounds that potentiate antibiotic activity in E. coli through inhibition of its primary RND transporter, AcrAB-TolC. Characterisation of resistant E. coli mutants and structural biology analyses indicate that the compounds bind to a unique site on the transmembrane domain of the AcrB L protomer, lined by key catalytic residues involved in proton relay. Molecular dynamics simulations suggest that the inhibitors access this binding pocket from the cytoplasm via a channel exclusively present in the AcrB L protomer. Thus, our work unveils a class of allosteric efflux-pump inhibitors that likely act by preventing the functional catalytic cycle of the RND pump.

Poly(cyclic imino ether)s beyond 2-substituted-2-oxazolines.

2-Oxazolines (2-OZO) are 5-membered cyclic imino ethers whose cationic ring-opening polymerization (CROP) mechanism and resulting polymer properties are extensively studied. However, also 6- and 7-membered cyclic imino ethers can be polymerized via CROP. Together with the much less studied 4- and 5-substituted main-chain chiral poly(2-oxazoline)s (P-2-OZO), these compounds are interesting monomers to enhance the versatility of (co)poly(cyclic imino ether)s. To emphasize the potential of such alternative cyclic imino ether monomers, we provide an overview on the polymerizations of 2-oxazine (2-OZI) and chiral 4- and 5-substituted 2-OZO as well as of selected properties of the resulting polymers. In addition, the hydrolysis of these polymers into the corresponding poly(alkylene imine)s will be addressed.

Penicillin sulfone inhibitors of class D beta-lactamases.

OXA beta-lactamases are largely responsible for beta-lactam resistance in Acinetobacter spp. and Pseudomonas aeruginosa, two of the most difficult-to-treat nosocomial pathogens. In general, the beta-lactamase inhibitors used in clinical practice (clavulanic acid, sulbactam, and tazobactam) demonstrate poor activity against class D beta-lactamases. To overcome this challenge, we explored the abilities of beta-lactamase inhibitors of the C-2- and C-3-substituted penicillin and cephalosporin sulfone families against OXA-1, extended-spectrum (OXA-10, OXA-14, and OXA-17), and carbapenemase-type (OXA-24/40) class D beta-lactamases. Three C-2-substituted penicillin sulfone compounds (JDB/LN-1-255, JDB/LN-III-26, and JDB/ASR-II-292) showed low K(i) values for the OXA-1 beta-lactamase (0.70 +/- 0.14 --> 1.60 +/- 0.30 microM) and demonstrated significant K(i) improvements compared to the C-3-substituted cephalosporin sulfone (JDB/DVR-II-214), tazobactam, and clavulanic acid. The C-2-substituted penicillin sulfones JDB/ASR-II-292 and JDB/LN-1-255 also demonstrated low K(i)s for the OXA-10, -14, -17, and -24/40 beta-lactamases (0.20 +/- 0.04 --> 17 +/- 4 microM). Furthermore, JDB/LN-1-255 displayed stoichiometric inactivation of OXA-1 (the turnover number, i.e., the partitioning of the initial enzyme inhibitor complex between hydrolysis and enzyme inactivation [t(n)] = 0) and t(n)s ranging from 5 to 8 for the other OXA enzymes. Using mass spectroscopy to study the intermediates in the inactivation pathway, we determined that JDB/LN-1-255 inhibited OXA beta-lactamases by forming covalent adducts that do not fragment. On the basis of the substrate and inhibitor kinetics of OXA-1, we constructed a model showing that the C-3 carboxylate of JDB/LN-1-255 interacts with Ser115 and Thr213, the R-2 group at C-2 fits between the space created by the long B9 and B10 beta strands, and stabilizing hydrophobic interactions are formed between the pyridyl ring of JDB/LN-1-255 and Val116 and Leu161. By exploiting conserved structural and mechanistic features, JDB/LN-1-255 is a promising lead compound in the quest for effective inhibitors of OXA-type beta-lactamases.

Water mediated construction of trisubstituted pyrazoles/isoxazoles library using ketene dithioacetals.

A small molecule library of alkyl, sulfone, and carboxamide functionalized pyrazoles and isoxazoles has been developed via a rapid sequential condensation of various alpha-acylketene dithioacetals (1a-o) with hydrazine hydrate or hydroxylamine hydrochloride, followed by oxidation of sulfide to sulfone using water as the reaction medium. An efficient and safe oxidation of sulfides (4/5a-o) to the corresponding sulfones (6/7a-o) using sodium per borate system in aqueous medium is reported. The concise and two step synthesis of trisubstituted pyrazoles and isoxazoles was investigated under variety of reaction condition. The newly developed methodology has the advantage of excellent yield and chemical purity with short reaction time using water as a solvent.

Impregnation of bone chips with antibiotics and storage of antibiotics at different temperatures: an in vitro study.

BACKGROUND: Allograft bone used in joint replacement surgery can additionally serve as a carrier for antibiotics and serve as a prophylaxis against infections. However, in vitro dose-response curves for bone chips impregnated with different kinds of antibiotics are not available. In addition, while it would be desirable to add the antibiotics to allograft bone chips before these are stored in a bone bank, the effects of different storage temperatures on antibiotics are unknown. METHODS: Five different antibiotics (cefazolin, clindamycin, linezolid, oxacillin, vancomycin) were stored, both as pills and as solutions, at -80 degrees C, -20 degrees C, 4 degrees C, 20 degrees C and 37 degrees C; in addition, bone chips impregnated with cefazolin and vancomycin were stored at -80 degrees C and -20 degrees C. After 1 month, 6 months and 1 year, the activity of the antibiotics against Staphylococcus epidermidis was measured using an inoculated agar. The diameter of the S. epidermidis-free zone was taken as a measure of antibiotic activity. In a separate experiment, in vitro dose-response curves were established for bone chips impregnated with cefazolin and vancomycin solutions at five different concentrations. Finally, the maximum absorbed amounts of cefazolin and vancomycin were established by impregnating 1 g of bone chips with 5 ml of antibiotic solution. RESULTS: A decrease of the S. epidermidis-free zone was seen with oxacillin and cefazolin solutions stored at 37 degrees C for 1 month, with vancomycin stored at 37 degrees C for 6 months and with cefazolin and oxacillin solutions stored at 20 degrees C for 6 months. The activity of the other antibiotic solutions, pills and impregnated bone chips was not affected by storage. The in vitro dose-response curves show that the free-zone diameter increases logarithmically with antibiotic concentration. The absorbed antibiotic amount of one gram bone chips was determined. CONCLUSIONS: Storage of antibiotics in frozen form or storage of antibiotic pills at temperatures up to 37 degrees C for 12 months does not affect their activity. However, storage of antibiotic solutions at temperatures above 20 degrees C does affect the activity of some of the antibiotics investigated. The in vitro dose-response curve can be used to determine the optimal concentration(s) for local application. It provides the opportunity to determine the antibiotic content of bone chips, and thus the amount of antibiotics available locally after application.

A temperature independent pH (TIP) buffer for biomedical biophysical applications at low temperatures.

A temperature independent pH buffer has been developed from a combination of buffers of opposite-sign temperature coefficients, and utility in low temperature spectroscopy and storage of pH sensitive compounds is demonstrated.

Comparative study of the effect of pharmaceutical additives on the elimination of antibiotic activity during the treatment of oxacillin in water by the photo-Fenton, TiO2-photocatalysis and electrochemical processes.

Synthetic pharmaceutical effluents loaded with the ß-lactam antibiotic oxacillin were treated using advanced oxidation processes (the photo-Fenton system and TiO2 photocatalysis) and chloride mediated electrochemical oxidation (with Ti/IrO2 anodes). Combinations of the antibiotic with excipients (mannitol or tartaric acid), an active ingredient (calcium carbonate, i.e. bicarbonate ions due to the pH) and a cleaning agent (sodium lauryl ether sulfate) were considered. Additionally, urban wastewater that had undergone biological treatment was doped with oxacillin and treated with the tested systems. The evolution of antimicrobial activity was monitored as a parameter of processes efficiency. Although the two advanced oxidation processes (AOPs) differ only in the way they produce OH, marked differences were observed between them. There were also differences between the AOPs and the electrochemical system. Interestingly, each additive had a different effect on each treatment. For water loaded with mannitol, electrochemical treatment was the most suitable option because the additive did not significantly affect the efficiency of the system. Due to the formation of a complex with Fe(3+), tartaric acid accelerated the elimination of antibiotic activity during the photo-Fenton process. For TiO2 photocatalysis, the presence of bicarbonate ions contributed to antibiotic activity elimination through the possible formation of carbonate and bicarbonate radicals. Sodium lauryl ether sulfate negatively affected all of the processes. However, due to the higher selectivity of HOCl compared with OH, electrochemical oxidation showed the least inhibited efficiency. For the urban wastewater doped with oxacillin, TiO2 photocatalysis was the most efficient process. These results will help select the most suitable technology for the treatment of water polluted with ß-lactam antibiotics.

Oxime-mediated facile access to 5-methylisoxazoles and applications in the synthesis of valdecoxib and oxacillin.

A palladium-catalyzed efficient synthesis of 5-methylisoxazoles via oxime-mediated functionalization of unactivated olefins is described. The reaction affords a variety of 5-methylisoxazoles in moderate to good yields. To further demonstrate the utility of the method, the rapid synthesis of valdecoxib and oxacillin is reported.

Thymoquinone vapor significantly affects the results of Staphylococcus aureus sensitivity tests using the standard broth microdilution method.

The broth microdilution (BMD) method is widely used for the determination of minimum inhibitory concentrations of antimicrobial agents, including volatile oils and their components. In this series of various experiments, we have demonstrated the influence of thymoquinone (TQ) vapor on the results of the BMD test performed with Staphylococcus aureus as a model organism. The spread of vapor from the TQ containing wells (32-512 µg/mL) caused the complete inhibition of staphylococcal growth in adjoining wells initially containing bacterium-inoculated pure Mueller-Hinton broth only and thus produced false positive results of the test. The ability of TQ to pass into the adjoined wells was subsequently confirmed by gas chromatography-mass spectrometry, whereas TQ at concentrations up to 84 µg/mL was detected in these wells after five hours. Based on these results, we suppose that vapors of TQ as well as of other naturally occurring volatile compounds and their mixtures (for example essential oils and plant extracts) can significantly influence results of the standard BMD assay. These observations, therefore, call for development of new appropriate BMD method suitable for assessment of antimicrobial activity of volatile substances.

Study of the complexation of oxacillin in 1-(4-carbomethoxypyrrolidone)-terminated PAMAM dendrimers.

The complexation of oxacillin to three generations of 1-(4-carbomethoxypyrrolidone)-terminated PAMAM dendrimers was studied with NMR in CD3OD and CDCl3. The stochiometries, which were determined from Job plots, were found to be both solvent- and generation-dependent. The dissociation constants (K(d)) and Gibbs energies for complexation of oxacillin into the 1-(4-carbomethoxypyrrolidone)-terminated PAMAM dendrimer hosts were determined by (1)H NMR titrations and showed weaker binding of oxacillin upon increasing the size (generation) of the dendrimer.

Degradation of antibiotics in water by non-thermal plasma treatment.

The decomposition of three ß-lactam antibiotics (amoxicillin, oxacillin and ampicillin) in aqueous solution was investigated using a dielectric barrier discharge (DBD) in coaxial configuration. Solutions of concentration 100 mg/L were made to flow as a film over the surface of the inner electrode of the plasma reactor, so the discharge was generated at the gas-liquid interface. The electrical discharge was operated in pulsed regime, at room temperature and atmospheric pressure, in oxygen. Amoxicillin was degraded after 10 min plasma treatment, while the other two antibiotics required about 30 min for decomposition. The evolution of the degradation process was continuously followed using liquid chromatography-mass spectrometry (LC-MS), total organic carbon (TOC) and chemical oxygen demand (COD) analyses.