Development and Evaluation of a Preliminary Screening Assay for Antibiotic Residues in Meat.

A preliminary screening assay based on a microbial chromogenic reaction was developed to detect common antibiotic residues in meat rapidly. The assay comprised two bioassays: one for Escherichia coli and another for Geobacillus stearothermophilus. The assay was optimized and evaluated for the simultaneous screening of 30 antibiotics from five common antibiotic classes (tetracyclines, aminoglycosides, macrolides, ß-lactams, and quinolones) found in meat. Extraction using phosphate-acetonitrile buffer (pH 7.2) and a delipidating treatment using n-hexane resulted in a high extraction efficacy for the five antibiotics, without affecting the microbial color reaction. A carrier, polyvinyl alcohol (0.1 g/mL); a cross-linking agent, boric acid-sodium tetraborate solution (pH 5.5); and a bacterial suspension with an initial optical density of 1.0 were the optimal embedding conditions for stability, microbial activity, and chromogenic efficiency. The assay exhibited a 6-month shelf life, with detection limits of 40-60, 60-140, 60-100, 20-40, and 40-180 µg/kg for tetracyclines, aminoglycosides, macrolides, ß-lactams, and quinolones, respectively, which met the European Commission (37/2010) requirements for antibiotic residue limits. Our assay results were confirmed using LC-MS/MS with 160 samples, revealing a good correlation. This study demonstrates a reliable, easy-to-use, and economical method for preliminary screening of antibiotic residues in meat. This method may find an immediate application in food safety and general testing laboratories.

Four new species of Estheria Robineau-Desvoidy (Diptera: Tachinidae) from China and Nepal, with a review of the East Palearctic and Oriental species.

The species of Estheria Robineau-Desvoidy (Diptera: Tachinidae) from the East Palearctic and Oriental regions are reviewed. Eighteen species are recognized: the fourteen previously described, E. acuta (Portschinsky, 1881), E. alticola Mesnil, 1967, E. bucharensis (Kolomiets, 1974), E. cinerella Mesnil, 1967, E. cristata (Meigen, 1826), E. decolor (Pandellé, 1896), E. flavipennis Herting, 1968, E. lacteipennis Mesnil, 1967, E. maculipennis Herting, 1968, E. magna (Baranov, 1935), E. nigripes (Villeneuve, 1920), E. pallicornis (Loew, 1873), E. petiolata (Bonsdorff, 1866) and E. picta (Meigen, 1826), and four species described as new to science, E. hirtinerva Zhang Shima sp. nov. (W China, Nepal), E. prostata Zhang Shima sp. nov. (W China, Nepal), E. tibetensis Zhang Shima sp. nov. (W China, Nepal) and E. wangi Zhang Liang sp. nov. (W China, Pakistan). Estheria acuta and E. decolor are newly recorded for China, E. magna is newly recorded for Malaysia, Pakistan and Vietnam, and E. pallicornis is newly recorded for Nepal. An identification key to the 18 species of Estheria so far known from the East Palearctic and Oriental regions is included, together with 126 figures of heads and habitus of males and females, and male terminalia and known distributions.

[A study of in vitro activity of daptomycin against 2679 Gram-positive cocci].

OBJECTIVE: To evaluate the in vitro activity of daptomycin against 2679 Gram-positive cocci. METHODS: A total of 2679 non-duplicate Gram-positive cocci isolates were collected from 17 teaching hospitals during January, 2010 and December, 2011. The minimal inhibitory concentrations (MICs) of daptomycin and other anti-microbial agents against 4 Gram-positive cocci were determined by micro-broth dilution method and agar dilution respectively. The data of drug susceptibility were analyzed by WHONET5.6 software. RESULTS: Methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase-negative Staphylococci (MRSCoN) detection rates were 45.8% and 84.2%, respectively. The susceptibility rates of sulfamethoxazole, chloramphenicol, erythromycin, tetracycline, clindamycin and rifampicin against MRSA were 93.1%, 85.5%, 13.8%, 26.6%, 63.2% and 50.0%, respectively. The susceptibility rates of daptomycin, vancomycin and linezolid against MRSA and MRSCoN were all 100.0%. The daptomycin MIC50 and MIC90 of MRSCoN and MRSA were 0.5 mg/L. The high level gentamicin resistance rate of 513 Enterococci isolates was 56.9%. The susceptibility rates of chloramphenicol and tetracycline were 76.0% and 44.1%, respectively. The susceptibility rates of tigecycline and daptomycin reached 100.0%. The MIC50 and MIC90 of daptomycin against 17 vancomycin-resistant Enterococci (VRE) were both 2 mg/L. The susceptibility rates of daptomycin against Streptococcus pneumoniae and ß-hemolytic Streptococcus were 100.0%. The prevalence of penicillin-nonsusceptible Streptococcus pneumoniae (PNSSP) was 63.1%. The MIC50 and MIC90 of daptomycin against PNSSP were 0.125 mg/L and 0.25 mg/L, respectively according to the breakpoint of oral penicillin. The MIC50 and MIC90 daptomycin against ß-hemolytic Streptococci were 0.008 mg/L and 0.032 mg/L. CONCLUSIONS: Daptomycin have excellent in vitro activity against common Gram-positive cocci, including multi-drug resistant bacteria. It may be a good choice for clinicians to treat drug-resistant Gram-positive cocci.

[Antimicrobial resistance and serotype distribution of Streptococcus pneumoniae isolated from multi-centers across China, 2010 - 2011].

OBJECTIVE: To investigate the trends of resistance of S. pneumoniae and to evaluate the potential coverage of pneumococcal conjugate vaccine. METHODS: The antibiotic susceptibility and serotype distribution of 471 pneumococcal strains isolated from pneumococcal diseases in 13 hospitals across China during 2010 to 2011 were studied. In vitro susceptibility to 15 antimicrobial agents was determined by agar dilution method. Serotyping of S. pneumoniae was performed by using latex and quelling reaction. Vaccine coverage by 7-, 10-, 13- and 23- valent conjugate vaccines was estimated by calculating the percentage of isolates that belonged to the serotypes included in the vaccines. RESULTS: Among all strains tested, 50.1% (236/471) was resistant to penicillin (Oral breakpoint, MIC ≥ 2 mg/L). Overall, 27.4% (129/471), 60.3% (284/471), 58.8% (277/471) and 18.5% (87/471) of S. pneumoniae were resistant to amoxicillin/clavulanate, cefaclor, cefuroxime and ceftriaxone, respectively.1.5% (7/471) of all stains were resistant to levofloxacin and 0.6% (3/471) of all strains were resistant to moxifloxacin. The resistance rates to other antibiotic agents, such as erythromycin, clindamycin, tetracycline, trimethoprim/sulfamethoxazole, and chloramphenicol, were 93.2% (439/471), 88.7% (417/471), 89.6% (422/471), 62.8% (296/471) and 22.1% (104/471), respectively. The most prevalent serotype was 19F (112, 23.8%), followed by 19A (63, 13.4%), 3 (48, 10.2%), 14 (43, 9.1%), 23F (29, 6.2%), 15 (25, 5.3%) and 6A (23, 4.9%). The potential coverage by 7- and 13-valent pneumococcal conjugate vaccines was 45.3% (213/471) and 76% (358/471), respectively. The potential coverage of PCV7 and PCV13 in children were 59.0% (72/122) and 86.9% (106/122), and the potential coverage of PCV7 and PCV13 in adult were 42.3% (94/222) and 73.4% (163/222). CONCLUSIONS: The antibiotic resistance of S. pneumoniae was serious in China, especially to tetracycline, erythromycin and clindamycin. The majority of serotypes 19A and 19F was penicillin-resistant. The potential coverage of PCV7 and PCV13 in children was higher than those in adult. PCV13 could cover most of the isolates, especially for penicillin-resistant S. pneumoniae.

TiO2-decorated graphene nanohybrids for fabricating an amperometric acetylcholinesterase biosensor.

This work describes a highly sensitive and rapid amperometric biosensor for organophosphate compounds (OPs) based on immobilization of acetylcholinesterase (AChE) on a novel TiO(2)-decorated graphene (TiO(2)-G) nanohybrid, which was constructed by in situ growth of TiO(2) nanoparticles (NPs) on the graphene sheet. The well-dispersed TiO(2) NPs eliminated the restacking of TiO(2)-G nanohybrids. Due to the integrating of TiO(2)-G nanohybrids, the as-prepared biosensor showed high affinity to acetylthiocholine (ATCl) with a Michaelis-Menten constant (K(m)) value of 0.22 mM, and rapid inhibition time (3 min). Further, based on the inhibition of OPs on the enzymatic activity of the immobilized AChE, and using carbaryl as a model compound, the inhibition of carbaryl was proportional to its concentration ranging from 0.001 to 0.015 and 0.015 to 2 µg mL(-1) with a detection limit of 0.3 ng mL(-1) (S/N = 3). The developed biosensor exhibited a good performance for organophosphate pesticide detection, including good reproducibility and acceptable stability, which provided a new and promising tool for the analysis of enzyme inhibitors.

Mapping quantitative trait loci for seed size traits in soybean (Glycine max L. Merr.).

Seed size traits in soybean--length, width and thickness--and their corresponding ratios--length-to-width, length-to-thickness and width-to-thickness--play a crucial role in determining seed appearance, quality and yield. In this study, an attempt was made to detect quantitative trait loci (QTL) for the aforementioned seed size traits in F(2:3), F(2:4) and F(2:5) populations from the direct and reciprocal crosses of Lishuizhongzihuang with Nannong 493-1, using multi-QTL joint analysis (MJA) along with composite interval mapping (CIM). A total of 121 main-effect QTL (M-QTL), six environmental effects, eight environment-by-QTL interactions, five cytoplasmic effects and 92 cytoplasm-by-QTL interactions were detected. Fifty-two common M-QTL across MJA and CIM, 21 common M-QTL in more than two populations and 5 M-QTL in all three populations showed the stability of the results. Five M-QTL had higher heritability, greater than 20%. In addition, 28 cytoplasm-by-QTL and 4 environment-by-QTL interactions were confirmed by CIM. Most M-QTL were clustered in eight chromosomal regions. Our results provide a good foundation for fine mapping, cloning and designed molecular breeding of favorable genes related to soybean seed size traits.

Enhanced direct electrochemistry of glucose oxidase and biosensing for glucose via synergy effect of graphene and CdS nanocrystals.

Integrating graphene-based composites with enzyme provides a potent strategy to enhance biosensor performance due to their unique physicochemical properties. Herein we report on the utilization of graphene-CdS (G-CdS) nanocomposite as a novel immobilization matrix for the enzymes, which glucose oxidase (GOD) was chosen as model enzyme. In comparison with the graphene sheet and CdS nanocrystal, G-CdS nanocomposite exhibited excellent electron transfer properties for GOD with the rate constant (k(s)) of 5.9 s(-1) due to the synergy effect of graphene sheet and CdS nanocrystals. Further, based on the decrease of the electrocatalytic response of the reduced form of GOD to dissolved oxygen, the obtained glucose biosensor displays satisfactory analytical performance over an acceptable linear range from 2.0 to 16 mM with a detection limit of 0.7 mM, and also prevents the effects of interfering species, which is suitable for glucose determination by real samples. These results mean that this immobilization matrix not only can be used for immobilizing GOD, but also can be extended to other enzymes and bioactive molecules, thus providing a promising platform for the development of biosensors.

Graphene enhanced electrochemiluminescence of CdS nanocrystal for H2O2 sensing.

Graphene-CdS (G-CdS) nanocomposites were successfully prepared by CdS nanocrystals (CdS NCs) formed in situ on the surface of graphene sheets, using graphene oxide (GO) sheets with rich negatively charged carboxylic acid groups as starting materials. Compared with pure CdS NCs, the presence of the graphene doped in G-CdS nanocomposites could facilitate the electrochemical redox process of CdS NCs; further, the as-prepared G-CdS nanocomposite can react with H(2)O(2) to generate strong and stable electrochemiluminescent (ECL) emission, which not only enhances its ECL intensity by about 4.3-fold but also decreases its onset potential for about 320 mV. The as-prepared solid-state ECL H(2)O(2) sensor shows acceptable linear response from 5 microM up to 1mM with a detection limit of 1.7 microM (S/N=3). The ECL H(2)O(2) sensor exhibits excellent reproducibility and long-term stability. Such a property would promote the potential application of the graphene as enhanced materials in fabricating sensors for chemical and biochemical analysis.

3D nanostructured Ni(OH)2 microspheres as an efficient immobilization matrix of Ru(bpy)3(2+) for high-performance electrochemiluminescence sensor.

The electrochemistry and electrochemiluminescence (ECL) of novel three-dimensional nanostructured Ru(bpy)(3)(2+)/Ni(OH)(2) microspheres were investigated for the first time. The negatively charged porous Ni(OH)(2) microspheres composed of Ni(OH)(2) nanowires were specifically designed to interact with Ru(bpy)(3)(2+). The large surface area and porous structure of Ni(OH)(2) microspheres enhance loading of Ru(bpy)(3)(2+) and mass transport of the model analyte, tripropylamine (TPA). Excellent ECL performance of the presented sensor was achieved including good stability and wide linear range from 7.7x10(-10) to 3.8x10(-3)M with the detection limit of 2.6x10(-10)M to TPA.