Concentrations Of Chloramphenicol Research Articles

Electrochemical treatment of chloramphenicol using Ti-Sn/γ-Al2O3 particle electrodes with a three-dimensional reactor

Three-dimensional Ti-Sn/γ-Al2O3 particle electrodes were prepared for the efficient degradation of chloramphenicol (CAP) in wastewater. To observe the surface morphology and structural characteristics of the Ti-Sn/γ-Al2O3 particle electrodes, Fourier transform infrared spectroscopy, X-ray fluorescence, scanning electron microscopy, and X-ray diffraction were used for characterization. Parameters affecting the degradation efficiency and energy consumption of the Ti-Sn/γ-Al2O3 particle electrodes, such as conductivity, initial pH of wastewater, current density, air flow, and initial CAP concentration (100mg·L−1), were examined. Results showed that the optimal conditions were 0.1 A current intensity, 1.0L·min−1 air flow, 6000μS·cm−1 conductivity, and pH 6. More than 70% of CAP was degraded under the optimal conditions. Based on the reaction intermediate products identified, a possible pathway for the electrochemical oxidation of CAP by the Ti-Sn/γ-Al2O3 particle electrodes was proposed.

Observation of residues in tissues of chickens exposed to low dietary concentrations of chloramphenicol

ABSTRACTTo investigate potential residues in tissues arising from naturally occurring low levels of chloramphenicol in plant material, feeding studies were conducted with chickens. A common chicken feed was prepared containing 0, 10, 50 and 200 μg kg−1 chloramphenicol and levels were confirmed by LC-MS/MS. Four separate groups of broiler chickens, eight animals in each group, were fed all their 35-day life with this contaminated feed. They were allowed ad libitum access to this feed and fresh water. After slaughtering the chickens, the residues in muscle and liver tissues were determined using GC/MS-NCI method. No residues were detected in tissues of animals from groups fed with feed containing 0, 10 or 50 µg kg−1. Low chloramphenicol residual concentrations were observed in a few of the muscle samples obtained from the group of chickens fed with feed containing chloramphenicol in added concentration 200 µg kg−1. No residues were detected in the remaining samples of this group. These results indicate that when residues of chloramphenicol are detected it is in all probability through illegal use.

Kinetic degradation of chloramphenicol in water by UV/persulfate system

Abstract Performances of chloramphenicol (CAP) degradation by direct ultraviolet (UV) irradiation, persulfate (PS) oxidation alone and UV irradiation-activated persulfate process (UV/PS) were systematically studied. UV/PS oxidation was superior over direct UV irradiation or PS oxidation alone. Both SO 4 − and HO were existing in UV/PS system, and SO 4 − was proved to be the primary radical species through the scavenging tests. The secondary order reaction rate constant between CAP and SO 4 − was estimated to be 1.33 × 10 10 M −1 s −1 . The CAP degradation fitted the pseudo-first-order kinetics well (R 2 > 0.95) in tests. Higher PS dosage, lower initial CAP concentration and acid pH promoted the CAP degradation. A maximum TOC removal of 31.7% was observed in 120 min at conditions of [CAP] 0 = 0.03 mM and [PS] 0 = 1.0 mM. At last, the electrical energy per order (EE/O) value in system was demonstrated to be 16.76 kWh/m 3 /order. Results indicated that the UV/PS system is potential alternative to control water pollution caused by emerging contaminants such as CAP.

Voltammetric determination of chloramphenicol using a carbon fiber microelectrode modified with Fe3O4 nanoparticles

An electrochemical microsensor for chloramphenicol (CAP) was fabricated by introducing magnetic Fe3O4 nanoparticles (NPs) onto the surface of activated carbon fibers. This microsensor exhibited increased electrochemical response toward CAP because of the synergetic effect of the Fe3O4 NPs and the carbon fibers. Cyclic voltammograms were acquired and displayed three stable and irreversible redox peaks in pH 7.0 solution. Under optimized conditions, the cathodic current peaks at −0.67 V (vs. Ag/AgCl). The calibration plot is linear in the 40 pM to 1 μM CAP concentration range, with a 17 pM detection limit (at a signal-to-noise ratio of 3). The sensor was applied to the determination of CAP in spiked sediment samples. In our perception, this electrocatalytic platform provided a useful tool for fast, portable, and sensitive analysis of chloramphenicol.

Novel single-stranded DNA binding protein-assisted fluorescence aptamer switch based on FRET for homogeneous detection of antibiotics

Herein, a smart single-stranded DNA binding protein (SSB)-assisted fluorescence aptamer switch based on fluorescence resonance energy transfer (FRET) was designed. The FRET switch was synthesized by connecting SSB labeled quantum dots (QDs@SSB) as donor with aptamer (apt) labeled gold nanoparticles (AuNPs@apt) as acceptor, and it was employed for detecting chloramphenicol (CAP) in a homogenous solution. In the assay, the interaction between core-shell QDs@SSB and AuNPs@apt leads to a dramatic quenching (turning off). After adding CAP in the detection system, AuNPs@apt can bind the target specifically then separate QDs@SSB with AuNPs@apt-target, resulting in restoring the fluorescence intensity of QDs (turning on). Consequently, the fluorescence intensity recovers and the recovery extent can be used for detection of CAP in homogenous phase via optical responses. Under optimal conditions, the fluorescence intensity increased linearly with increasing concentrations of CAP from 0.005 to 100ngmL−1. The limit of this fluorescence aptamer switch was around 3pgmL−1 for CAP detection. When the analyte is changed, the assay can be applied to detect other targets only by changing relative aptamer in AuNPs@apt probe. Furthermore, it has potential to be served as a simple, sensitive and portable platform for antibiotic contaminants detection in biological and environmental samples.

Elimination of Chloramphenicol by Tiger Shrimp (Penaeus monodon) and White Shrimp (Litopenaeus vannamei)

Chloramphenicol (CAP) has been illegally used in many shrimp farms in South East Asia, including Indonesia. We performed an experiment of elimination simulation of CAP in tiger shrimp (Penaeus monodon) and white shrimp (Litopenaeus vannamei). After 5 days of depuration process, the concentration of CAP in P. monodon decreased to 94.85% (muscle), 97.98% (cephalothoraxes), and 90.30% (exoskeleton). The elimination half-life of CAP in P monodon was 0.596 day in the muscle, 0.716 day in cephalothorax, and 0.437 day in exoskeleton. On the other hand, concentrations of CAP in L. vannamei decreased to 97.74% (muscle), 90.30% (cephalothoraxes), and 97.63% (exoskeleton). The elimination half-life of CAP in L. vannamei was 0.6624 day (muscle), 0.859 day (cephalothorax), and 0.796 day (exoskeleton). CAP was retained better by P. monodon compared to L. vannamei.

Solid Phase Extraction of Trace Amounts of Chloramphenicol on the Silica Gel Surface Modified with Octadecyl Groups

Background. Chloramphenicol (CAP) is a broad spectrum antibiotic. It’s widely used in various fields of veterinary and can be accumulated in food of animal origin. A minimum required performance limit (MRPL) for CAP in food is significantly restricted in the EU and the USA. Most modern methods make it difficult to determine the trace amounts of the drug from various matrices without concentration. The method of liquid-liquid extraction (LLE) may be accompanied by loss of trust component. It is therefore advisable to use solid phase analyte extraction to increase the determination sensitivity by instrumental methods and CL withdrawal stability.Objective. Development of the solid phase extraction method of chloramphenicol from honey, followed by enzyme linked immunoassay.Methods. Quantitative determination of chloramphenicol was determined using enzyme linked assay (ELISA) test-kit for determination of chloramphenicol in foods, provided by LLC “XEMA”. Solid phase extraction of chloramphenicol from honey samples was studied on silica gel surface modified with octadecyl groups (SiO2-C18), “Agilent”. This method of solid phase extraction was carried out on samples of honey, that previously checked by ELISA using LLE for sample preparation.Results. Our results showed the possibility of solid phase extraction of CAP on the surface of the silica gel with oktadecyl groups. The optimal conditions for extraction the analyte on the surface of sorbent were found and the eluation condition for CAP was studied. We tested the method of solid phase extraction of CAP from honey matrics on control materials – honey samples with known concentrations of CAP, that were bought by LLC “XEMA”.Conclusions. Solid phase extraction of CAP could be used for CAP extraction form honey. The proposed method of sample preparation reduces the time of preparation for honey samples. This method is perspective for developing the method of simultaneous concentration of antibiotics from different groups followed by ELISA determination.

A novel photonic sensor for the detection of chloramphenicol

A novel photonic sensor using a self-cross-linked imprinting close-packed opal (CPO) as a recognition element was developed for the detection of chloramphenicol (CAP). The self-cross-linked imprinting CPO film was consisted of monodisperse molecular imprinted – N-hydroxymethylacrylamide particles (MI-HAM particles) with self-assembling and self-crosslinking properties. A dilute dispersion of these particles was self-assembled to formation of the highly ordered CPO structure, and at the same time the neighboring particles reacted to form covalent bond to stabilize the CPO structure at the air/dispersion. Thus the obtained self-cross-linked imprinting CPO was characterized by a highly stable three-dimensional (3D) CPO structure without the interference of bulk hydrogel matrix, in which numerous CAP recognition sites were dispersed through the molecular imprinted process. The inherent high affinity of the recognition sites allowed the self-cross-linked imprinting CPO to recognize CAP with high specificity, and changes of the periodic structure enabled the self-cross-linked imprinting CPO to transfer the recognition events into readable optical signals. Then the self-cross-linked imprinting CPO film was packed into a reaction cell with an optical spectrometer to establish a novel photonic sensor. A linear relationship was found between the diffraction intensity decrease and CAP concentration in the range from 2ngmL−1 to 512ngmL−1, whereas there was no obvious optical change for CAP analogues, thus indicating that the sensor had selective and sensitive response to CAP molecules. Furthermore, the sensor was applied successfully to detect CAP in drinking water samples. As a result, the developed sensor might offer a potential alternative in routine supervision for residue due to its convenience, low cost, reusability, and high sensitivity as well as selectivity.

Synchronized separation, concentration and determination of trace chloramphenicol, thiamphenicol and florfenicol in food by using polyoxyethylene cetyl ether-salt aqueous two-phase system coupled with high-performance liquid chromatography

As a novel and green pretreatment technique to trace samples, polyoxyethylene cetyl ether (POELE20)–(NH4)2SO4 aqueous two-phase extraction system was coupled with high-performance liquid chromatography to analyse synchronously chloramphenicol (CAP), thiamphenicol (TAP) and florfenicol (FF) in chicken and pork samples. It was found that the extraction efficiency (E%) and enrichment factor (F) of the three antibiotics were influenced by the types of salts, the concentration of salt, the concentration of POELE20, system temperature and pH. The final optimal condition was as following: the phase-forming salt is (NH4)2SO4, the concentration of (NH4)2SO4 is 0.141 g mL−1, the concentration of POELE20 is 0.03 g mL−1, the temperature is 298.15 K, and the system pH is 4.5. This POELE20–(NH4)2SO4 ATPS was applied to separate and enrich three antibiotics in real sample under the optimal conditions, and it was found that the recovery was 97.20–102.00 % with a RSD of 0.61–4.85 %. The limit of detection for CAP, TAP and FF were 0.10, 0.50 and 0.50 μg kg−1, and the limit of quantitation for CAP, TAP and FF was 0.15, 1.50 and 1.50 μg kg−1. Seven times the experiments were used to verify the repeatability and veracity of this method, and the RSD for the intra-day and inter-day were 1.13–3.22 and 1.74–4.72 %.

Adaptive responses to cefotaxime treatment in ESBL-producing Escherichia coli and the possible use of significantly regulated pathways as novel secondary targets.

The aim of the study was to determine how ESBL-producing Escherichia coli change the expression of metabolic and biosynthesis genes when adapting to inhibitory concentrations of cefotaxime. Secondly, it was investigated whether significantly regulated pathways constitute putative secondary targets that can be used to combat the resistant bacteria. Strains of E. coli MG1655 encoding blaCTX-M-1 from an IncI1 plasmid and from the chromosome were challenged with cefotaxime corresponding to inhibitory concentrations, and transcriptional patterns were compared with growth without or with very low concentrations of cefotaxime by RNA sequencing. Significantly regulated pathways were inhibited with suitable inhibitors, or genes encoding the enzymes of the regulated pathways were knocked out. The ability of the bacteria to grow in the presence of cefotaxime was determined. Chequerboard assays were utilized to confirm synergies between treatments. Genes belonging to 16 different functional gene classes were significantly regulated. Protein and peptidoglycan syntheses were up-regulated and low concentrations of chloramphenicol or d-cycloserine, targeting these systems, strongly reduced the MIC of cefotaxime (>32-fold). Inhibition and/or mutations in other genes that were significantly regulated, belonging to energy synthesis, purine synthesis, proline uptake or potassium uptake, also rendered the resistant bacteria more susceptible to cefotaxime. The results show that ESBL-producing E. coli adapt to treatment with cefotaxime by changing their gene expression patterns and furthermore that targeting regulated adaptive pathways may be a suitable way to identify targets for drugs that will specifically inhibit the resistant bacteria.

Removal of Chloramphenicol and Simultaneous Electricity Generation by Using Microbial Fuel Cell Technology

The release of antibiotics into aquatic environments and its related long-term side effects have attracted great attention. As one of the most commonly used antibiotics in China, nitroaromatic antibiotic chloramphenicol (CAP) can be detected in aquatic environments. CAP removal efficiency in the anode chamber of microbial fuel cell (MFC) and the effect of CAP on the electricity output of MFC were studied in this paper. As compared to control experiments including open circuit MFC, no extra carbon source MFC, and abiotic MFC, the removal efficiency of CAP in normal MFC was the most outstanding. However, as the concentration of CAP increased, the removal efficiency is on the decline which is attributed to the CAP load increased. At an initial concentration lower than 30 mg L-1, the electroactive biofilm-based MFC is robust with more than 95% voltage output maintained, but the voltage output dropped dramatically in antibiotic concentrations higher than 50 mg L-1. An exponential relationship was found between the inhibition ratios of the MFC and the CAP concentrations in the studied concentration range. The findings about the CAP removal and the effects of CAP on the electricity output in two-chambered MFC in this work would have great importance to practical antibiotics wastewater treatment.

Novel bioassay using Bacillus megaterium to detect tetracycline in milk

Tetracyclines are used for the prevention and control of dairy cattle diseases. Residues of these drugs can be excreted into milk. Thus, the aim of this study was to develop a microbiological method using Bacillus megaterium to detect tetracyclines (chlortetracycline, oxytetracycline and tetracycline) in milk. In order to approximate the limits of detection of the bioassay to the Maximum Residue Limit (100μg/l) for milk tetracycline, different concentrations of chloramphenicol (0, 1000, 1500 and 2000μg/l) were tested. The detection limits calculated were similar to the Maximum Residue Limits when a bioassay using B. megaterium ATCC 9885 spores (2.8×108spores/ml) and chloramphenicol (2000μg/l) was utilized. This bioassay detects 105μg/l of chlortetracycline, 100μg/l of oxytetracycline and 134μg/l of tetracycline in 5h. Therefore, this method is suitable to be incorporated into a microbiological multi-residue system for the identification of tetracyclines in milk.

Modulation of Membrane Influx and Efflux in Escherichia coli Sequence Type 131 Has an Impact on Bacterial Motility, Biofilm Formation, and Virulence in a Caenorhabditis elegans Model.

Energy-dependent efflux overexpression and altered outer membrane permeability (influx) can promote multidrug resistance (MDR). The present study clarifies the regulatory pathways that control membrane permeability in the pandemic clone Escherichia coli sequence type 131 (ST131) and evaluates the impact of efflux and influx modulations on biofilm formation, motility, and virulence in the Caenorhabditis elegans model. Mutants of two uropathogenic E. coli (UPEC) strains, MECB5 (ST131; H30-Rx) and CFT073 (ST73), as well as a fecal strain, S250 (ST131; H22), were in vitro selected using continuous subculture in subinhibitory concentrations of ertapenem (ETP), chloramphenicol (CMP), and cefoxitin (FOX). Mutations in genes known to control permeability were shown for the two UPEC strains: MECB5-FOX (deletion of 127 bp in marR; deletion of 1 bp and insertion of an IS1 element in acrR) and CFT073-CMP (a 1-bp deletion causing a premature stop in marR). We also demonstrated that efflux phenotypes in the mutants selected with CMP and FOX were related to the AcrAB-TolC pump, but also to other efflux systems. Alteration of membrane permeability, caused by underexpression of the two major porins, OmpF and OmpC, was shown in MECB5-ETP and mutants selected with FOX. Lastly, our findings suggest that efflux pump-overproducing isolates (CMP mutants) pose a serious threat in terms of virulence (significant reduction in worm median survival) and host colonization. Lack of porins (ETP and FOX mutants) led to a high level of antibiotic resistance in an H30-Rx subclone. Nevertheless, this adaptation created a physiological disadvantage (decreased motility and ability to form biofilm) associated with a low potential for virulence.

Label-free and sensitive aptasensor based on dendritic gold nanostructures on functionalized SBA-15 for determination of chloramphenicol

A highly sensitive and low-cost electrochemical aptasensor was developed for the determination of chloramphenicol (CAP). The system was based on a CAP-binding aptamer, a molecular recognition element, and 1,4-diazabicyclo[2.2.2]octane (DABCO)-supported mesoporous silica SBA-15 on the surface of a screen-printed graphite electrode for formation of dendritic gold nanostructures and improving the performance and conductivity of the biosensor. Hemin has been applied as an electrochemical indicator which interacted with the guanine bases of the aptamer. In the absence of CAP, hemin binds to the aptamer and produces a weak differential pulse voltammetric (DPV) signal. The presence of CAP led to stabilization of the folded aptamer, which generated an amplified DPV signal. The peak current of hemin increased linearly with the concentration of CAP. Under optimal conditions, two linear ranges were obtained from 0.03 to 0.15μM and 0.15 to 7.0μM, respectively, and the detection limit was 4.0 nM. The prepared biosensor has good selectivity against other non-target drugs. Thus, the sensor could provide a promising platform for the fabrication of aptasensors. The feasibility of using this aptasensor was demonstrated by determination of CAP in a human blood serum sample.

Phytotoxicity of veterinary antibiotics to seed germination and root elongation of crops

Large quantities of veterinary antibiotics (VAs) are being used worldwide in agricultural fields through wastewater irrigation and manure application. They cause damages to the ecosystem when discharged into the environment, but there is a lack of information on their toxicity to plants and animals. This study evaluated the phytotoxic effects of five major VAs, namely tetracycline (TC), sulfamethazine (SMZ), norfloxacin (NOR), erythromycin (ERY) and chloramphenicol (CAP), on seed germination and root elongation in lettuce, tomato, carrot and cucumber, and investigated the relationship between their physicochemical properties and phytotoxicities. Results show that these compounds significantly inhibited root elongation (p<0.05), the most sensitive endpoint for the phytotoxicity test. TC was associated with the highest level of toxicity, followed by NOR, ERY, SMZ and CAP. Regarding crop species, lettuce was found to be sensitive to most of the VAs. The median effect concentration (EC50) of TC, SMZ, NOR, ERY and CAP to lettuce was 14.4, 157, 49.4, 68.8 and 204mg/L, respectively. A quantitative structure-activity relationship (QSAR) model has been established based on the measured data. It is evident that hydrophobicity was the most important factor governing the phytotoxicity of these compounds to seeds, which could be explained by the polar narcosis mechanism. Lettuce is considered a good biomarker for VAs in the environment. According to the derived equation, phytotoxicities of selected VA compounds on different crops can be calculated, which could be applicable to other VAs. Environmental risks of VAs were summarized based on the phytotoxicity results and other persistent factors.

Electrochemical simultaneous assay of chloramphenicol and PCB72 using magnetic and aptamer-modified quantum dot-encoded dendritic nanotracers for signal amplification

The article describes a multiplex aptamer based voltammetric assay for the food pollutants chloramphenicol (CAP) and polychlorinated biphenyl-72 (PCB72). The method is based on the displacement of a nanotracer (an aptamer-labeled magnetic dendritic probe) by the analytes which cause the release of the corresponding encoded nanotracers. Thiolated aptamers of CAP and PCB72 were first self-assembled on magnetic gold nanoparticles (Fe3O4@Au) as capture probes to concentrate the target analytes CAP and PCB72, respectively. Next, their hybridized complementary strands (cDNA1 or cDNA2) and a dendritic polymerase were linked to quantum dots (CdS or PbS) to form the respective nanotracers. Finally, encoded composite magnetic probes were obtained through hybridization reaction between aptamers and cDNAs. Once CAP and PCB72 are recognized by the composite probes, the nanotracers are released into the supernatant where they can be detected simultaneously by voltammetry of the metal ion markers Cd(II) and Pb(II) at −0.81 and −0.57 V (vs. Ag/AgCl), respectively. The concentration measured for Cd(II) and Pb(II) are directly proportional to the concentrations of CAP and PCB72, respectively, in the range from 0.001 to 100 ng mL−1. The detection limits for CAP and PCB72 are 0.33 and 0.35 pg mL−1, respectively (at an S/N ratio of 3), which is 2 to 3 orders of magnitude lower than the routinely performed and commercially available ELISA. The method is perceived to possess large potential in that it may be applied to other antibiotics by using the appropriate aptamers.

Antibacterial and antibiotic potentiating activity of Vangueria madagascariensis leaves and ripe fruit pericarp against human pathogenic clinical bacterial isolates

This study aimed to assess the antibacterial and antibiotic potentiating property of Vangueria madagascariensis (VM) (fruit and leaf extracts) against 10 clinical isolates. A microdilution broth susceptibility assay for bacteria was used for the determination of the minimum inhibitory concentration (MIC) and associated with antibiotics to evaluate any synergistic effect. VM extracts were found to potentiate the activity of 3 conventional antibiotics. Chloramphenicol and Ciprofloxacin showed no activity against Acinetobacter spp. but when mixed with VM (in a ratio of 50% VM extracts: 30% antibiotic), showed potentiating effect. The methanolic fruit extract at lower concentration of Chloramphenicol (30%) gave better synergistic effect (MIC = 3.75 μg/mL) as compared to 50% (MIC = 12.5 μg/mL). With Gentamicin, no activity was detected with leaf decoction but other extracts (methanolic leaf/fruit extract and fruit decoction) showed enhancement (MIC- 0.47, 7.5 and 15 μg/mL respectively). Interestingly, Chloramphenicol showed no activity against MRSA, but when mixed with VM, produced low MICs (<0.39–0.78 μg/mL with 50% antibiotic and from <0.47 to 0.94 μg/mL with 30% antibiotic). Combining Gentamicin with VM extracts showed an enhancement in the potentiating activity against MRSA. In conclusion, the observed antimicrobial property of VM tend to suggest a promising alternative and complementary strategy to manage bacterial infections and hence can open new avenues for further research using traditional medicinal food plant.

A sensitive electrochemical aptasensor for multiplex antibiotics detection based on high-capacity magnetic hollow porous nanotracers coupling exonuclease-assisted cascade target recycling

A multiplex electrochemical aptasensor was developed for simultaneous detection of two antibiotics such as chloramphenicol (CAP) and oxytetracycline (OTC), and high-capacity magnetic hollow porous nanotracers coupling exonuclease-assisted target recycling was used to improve sensitivity. The cascade amplification process consists of the exonuclease-assisted target recycling amplification and metal ions encoded magnetic hollow porous nanoparticles (MHPs) to produce voltammetry signals. Upon the specific recognition of aptamers to targets (CAP and OTC), exonuclease I (Exo I) selectively digested the aptamers which were bound with CAP and OTC, then the released CAP and OTC participated new cycling to produce more single DNA, which can act as trigger strands to hybrid with nanotracers to generate further signal amplification. MHPs were used as carriers to load more amounts of metal ions and coupling with Exo I assisted cascade target recycling can amplify the signal for about 12 folds compared with silica based nanotracers. Owing to the dual signal amplification, the linear range between signals and the concentrations of CAP and OTC were obtained in the range of 0.0005–50ngmL−1. The detection limits of CAP and OTC were 0.15 and 0.10ngmL−1 (S/N=3) which is more than 2 orders lower than commercial enzyme-linked immunosorbent immunoassay (ELISA) method, respectively. The proposed method was successfully applied to simultaneously detection of CAP and OTC in milk samples. Besides, this aptasensor can be applied to other antibiotics detection by changing the corresponding aptamer. The whole scheme is facile, selective and sensitive enough for antibiotics screening in food safety.

Influence of antibiotic pressure on bacterial bioluminescence, with emphasis on Staphylococcus aureus

Bioluminescence imaging is used for longitudinal evaluation of bacteria in live animals. Clear relations exist between bacterial numbers and their bioluminescence. However, bioluminescence images of Staphylococcus aureus Xen29, S. aureus Xen36 and Escherichia coli Xen14 grown on tryptone soy agar in Etests demonstrated increased bioluminescence at sub-MICs of different antibiotics. This study aimed to further evaluate the influence of antibiotic pressure on bioluminescence in S. aureus Xen29. Bioluminescence of S. aureus Xen29, grown planktonically in tryptone soy broth, was quantified in the absence and presence of different concentrations of vancomycin, ciprofloxacin, erythromycin or chloramphenicol and was related to expression of the luxA gene under antibiotic pressure measured using real-time PCR. In the absence of antibiotics, staphylococcal bioluminescence increased over time until a maximum after ca. 6h of growth, and subsequently decreased to the detection threshold after 24h of growth owing to reduced bacterial metabolic activity. Up to MICs of the antibiotics, bioluminescence increased according to a similar pattern up to 6h of growth, but after 24h bioluminescence was higher than in the absence of antibiotics. Contrary to expectations, bioluminescence per organism (CFU) after different growth periods in the absence and at MICs of different antibiotics decreased with increasing expression of luxA. Summarising, antibiotic pressure impacts the relation between CFU and bioluminescence. Under antibiotic pressure, bioluminescence is not controlled by luxA expression but by co-factors impacting the bacterial metabolic activity. This conclusion is of utmost importance when evaluating antibiotic efficacy in live animals using bioluminescent bacterial strains.

Switch-on fluorescence scheme for antibiotics based on a magnetic composite probe with aptamer and hemin/G-quadruplex coimmobilized nano-Pt–luminol as signal tracer

A selective and facile fluorescence “switch-on” scheme is developed to detect antibiotics residues in food, using chloramphenicol (CAP) as model, based on a novel magnetic aptamer probe (aptamer–Pt–luminol nanocomposite labeled with hemin/G-quadruplex). Firstly, the composite probe is prepared through the immuno-reactions between the capture beads (anti-dsDNA antibody labeled on magnetic Dynabeads) and the nanotracer (nano-Pt–luminol labeled with double-strand aptamer, as ds-Apt, and hemin/G-quadruplex). When the composite probe is mixed with CAP, the aptamer preferentially reacted with CAP to decompose the double-strand aptamer to ssDNA, which cannot be recognized by the anti-dsDNA antibody on the capture probes. Thus, after magnetic separation, the nanotracer can be released into the supernatant. Because the hemin/G-quadruplex and PtNPs in nanotracer can catalyze luminol–H2O2 system to emit fluorescence. Thus a dual-amplified “switch-on” signal appeared, of which intensity is proportional to the concentration of CAP between 0.001 and 100ngmL−1 with detection limit of 0.0005ngmL−1 (S/N=3). Besides, our method has good selectivity and was employed for CAP detection in real milk samples. The results agree well with those from conventional gas chromatograph–mass spectrometer (GC–MS). The switch-on signal is produced by one-step substitution reaction between aptamer in nanotracer and target. When the analyte is changed, the probe can be refabricated only by changing the corresponding aptamer. Thus, all features above prove our strategy to be a facile, feasible and selective method in antibiotics screening for food safety.