Development of novel antibodies for detection of mobile colistin-resistant bacteria contaminated in meats.

The recent discovery and rapid spread of mobile colistin-resistant gene, mcr-1, among bacteria isolated from a broad range of sources is undermining our ability to treat bacterial infections and threatening human health and safety. To prevent further transfer of colistin resistance, practical and reliable methods for mcr-1-containing bacteria are need. In this study, standards and novel polyclonal and monoclonal antibodies (mAbs) against MCR-1 were developed. Among nine mAbs, three were MCR-1 specific and six cross-reacted with both MCR-1 and MCR-2. A sandwich enzyme-linked immunosorbent assay (ELISA) was established using the polyclonal antibody as a capturer and the mAb MCR-1-7 as a detector. The assay had a limit of detection of 0.01 ng/mL for MCR-1 and 0.1 ng/mL for MCR-2 in buffer with coefficients of variation (CV) less than 15%. When applied to ground beef, chicken and pork, this ELISA identified samples inoculated with less than 0.4 cfu/g of meat, demonstrating its strong tolerance to complex food matrices. To our knowledge, this is the first immunoassay developed for MCR-1 and MCR-2. It should be useful for prompt and reliable screening of meat samples contaminated with plasmid-borne colistin-resistant bacteria, thus reducing human risk of foodborne infections with possibly no antibiotic treatment options.

Detection of Shiga Toxin 2 Produced by Escherichia coli in Foods Using a Novel AlphaLISA.

Amplified luminescent proximity homogenous assay-linked immunosorbent assay (AlphaLISA) is comprised of a bead-based immunoassay that is used for small molecule detection. In this study, a novel AlphaLISA was developed and optimized for the detection of Shiga-toxin 2 (Stx2). Efficacy and sensitivity trials showed the AlphaLISA could detect ≥0.5 ng/mL of purified Stx2, which was comparable to the industry-standard enzyme-linked immunosorbent assay (ELISA) tests for Stx2 detection. In addition, evaluation of Shiga toxin-producing Escherichia coli (STEC)-inoculated Romaine lettuce and ground beef samples demonstrated that both the AlphaLISA and the ELISA were able to discern uninoculated samples from 1× and 10× diluted samples containing ~10 CFU/mL of STEC enriched in modified tryptic soy broth with mitomycin C for 16 h. Overall, the increased signal-to-noise ratios indicated a more robust signal was produced by the AlphaLISA compared to the ELISA and the delineation of higher toxin concentrations without the need for sample dilution implied a greater dynamic range for the AlphaLISA. Implementation of the newly developed AlphaLISA will allow for more rapid analysis for Stx2 with less manual manipulation, thus improving assay throughput and the ability to automate sample screening while maintaining detection limits of 0.5 ng/mL.

Suitability of a magnetic particle immunoassay for the analysis of PBDEs in Hawaiian euryhaline fish and crabs in comparison with gas chromatography/electron capture detection-ion trap mass spectrometry.

A gas chromatograph/electron capture detector-ion trap mass spectrometer (GC/ECD-ITMS) was used for the determination of polybrominated diphenyl ethers (PBDEs) in euryhaline fish and crabs. GC/ECD-ITMS results showed that average recoveries from the spiked fish samples are in a range of 58-123% with relative standard deviations (RSDs) of 5-19%. PBDE concentrations obtained from GC/ECD-ITMS ranged from 28 ng/g to 1845 ng/g lipid weight (lw) in all aquatic species collected from Hawaiian brackish waters. The general BDE congener concentration profile observed in this study is BDE-47>BDE-100>BDE-154>BDE-99>BDE-153>BDE-28>BDE-183. The ELISA results expressed as BDE-47 equivalents correlated well with those of GC/ECD-ITMS, with a correlation coefficient (R(2)=0.68) and regression coefficient (slope=0.82). Comparison of ELISA with GC/ECD-ITMS results demonstrated that ELISA provides a timely and cost-effective method to screen PBDEs in fish and crab samples.

Development of a magnetic particle-based enzyme immunoassay for the determination of penoxsulam in water.

A competitive enzyme-linked immunoassay (ELISA) for the quantitation of Penoxsulam [2-(2,2-difluoroethoxy)-6-(trifluoromethyl-N-(5,8-dimethoxy[1,2,4]triazolo[1,5-c]pyrimidin-2-yl))benzenesulfonamide] in ground and surface waters was developed. This immunoassay utilizes magnetic particles as the solid phase to which polyclonal rabbit anti-Penoxsulam antibodies are attached. The ELISA has an estimated detection limit of 0.17 ppb (microg/mL) of Penoxsulam in water. Specificity studies indicate that the antibody can distinguish Penoxsulam from its major metabolites and structurally similar pesticides. Interference studies indicate that the ELISA has a wide tolerance of sample pH and salinity and for compounds commonly found in surface and ground waters. The ELISA was shown to compare favorably to LC-MS/MS on ground and surface water samples (r(2) = 0.957). The various studies performed demonstrate the usefulness of the ELISA technique as a rapid and high-throughput analytical method for the cost-effective monitoring of water samples.

Development of a magnetic particle immunoassay for polybrominated diphenyl ethers and application to environmental and food matrices.

A sensitive magnetic particle enzyme-linked immunoassay (ELISA) was developed to analyze polybrominated diphenyl ethers (PBDEs) in water, milk, fish, and soil samples. The assay was rapid and can be used to analyze fifty samples in about 1h after sample cleanup. The assay has a limit of detection (LOD) below 0.1 ppb towards the following brominated diphenyl ether (BDE) congeners: BDE-47, BDE-99, BDE-28, BDE-100, and BDE-153, with the LOD approximately the same as GC-NCI-MS. The congeners most readily recognized in the ELISA were BDE-47 and BDE-99 with the cross-reactivities of BDE-28, BDE-100, and BDE-153 being less than 15% relative to BDE-47. As anticipated, the sensitivities are proportional to the similarities between the hapten structure and the BDE congener structure. Some oxygenated congeners with structural similarity to the hapten showed high to moderate cross-reactivities. Very low cross-reactivity was observed for other PBDEs or chlorinated environmental contaminants. The assay gave good recoveries of PBDEs from spiked water samples and a very small within and between day variance. Comparison with GC-NCI-MS demonstrated the ELISA method showed equivalent precision and sensitivity, with better recovery. The lower recovery of the GC-NCI-MS method could be caused by the use of an internal standard other than an isotopically substituted material that could not be used because of the fragmentation pattern observed by this method. The cleanup methods prior to ELISA were matrix dependent, no pretreatment was needed for environmental water samples, while fish, milk, and soil samples required various degrees of cleanup. Analysis of this wide variety of environmental samples by both ELISA and GC-MS demonstrated ELISA provides a timely and cost-effective method to screen for PBDEs in a variety of samples.

Measurement of triclosan in water using a magnetic particle enzyme immunoassay.

A sensitive magnetic particle-based immunoassay to determine triclosan [5-chloro-2-(2,4-dichlorophenoxy)phenol] in drinking water and wastewater was developed. Rabbit antiserum was produced by immunizing the rabbit with 6-[5-chloro-2-(2,4-dichlorophenoxy)phenoxy]hexanoic acid-keyhole limpet hemocyanin. Horseradish peroxidase was conjugated with 4-[3-bromo-4-(2,4-dibromophenoxy)phenoxy]butyric acid via N-hydroxysuccinimide (NHS) and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC). The triclosan antibody was coupled to magnetic particles via the NHS/EDC reaction. The antibodies were able to recognize some structurally related polybrominated biphenyl ethers but did not recognize various common pollutants that were less similar to the hapten. The ELISA could detect triclosan in standard solution (25% methanol/H2O v/v) at 20 ppt and its metabolite, methyl-triclosan, at 15 ppt. Water samples from different treatment stages were prepared to contain 25% methanol and analyzed directly without any sample extraction or preconcentration. The results showed that recoveries were >80% and the % CV was <10%, demonstrating the assay was both accurate and precise. Application of the triclosan ELISA to water treatment plants showed that tap water at various purification stages had low concentrations of triclosan (<20 ppt) and required an increased sample size for appropriate detection and measurement. Application of ELISA to the wastewater treatment plants (WWTP) demonstrated high concentrations of triclosan (in general, >3000 ppt in water entering the WWTP) with the levels decreasing as the water proceeded through the processing plant (<500 ppt at outflow sewage). The ELISA measurement was shown to be equivalent to the more specific GC-MS analysis on a number of wastewater treatment samples with a high degree of correlation, with the exception of a few samples with very high triclosan concentrations (>5000 ppt). Measurement of methyl-triclosan (in WWTP) using GC-MS demonstrated the levels of this compound to be low. In summary, a rapid, sensitive, accurate, and precise magnetic particle-based immunoassay has been developed for triclosan analysis, which can serve as a cost-effective monitoring tool for various water samples.

A radioligand binding assay for antitubulin activity in tumor cells.

The benzamide RH-5854 is shown to be highly potent toward tumor cells and to arrest nuclear division by a highly specific covalent binding to the beta-subunit of tubulin in the colchicine binding region. Binding of 3H-RH-5854 to beta-tubulin in HCT-116 colon cancer cells is saturable and has been exploited in the development of a cell-based competitive binding assay, which allows antitubulin effects to be detected in whole cells. 3H-RH-5854 binding is strongly inhibited by preincubating the cells with compounds that bind to the colchicine site and with paclitaxel. Binding of 3H-RH-5854 is enhanced by preincubating the cells with vinblastine but not by other agents that bind at or near the vinblastine site (ansamitocin P-3 and phomopsin A). Various cytotoxic agents that do not act on tubulin do not affect binding of 3H-RH-5854 in HCT-116 cells, demonstrating specificity of the assay for detection of antitubulin activity. As an alternative to traditional assays that employ isolated brain tubulin, the 3HRH-5854 binding assay enables screening for antitubulin effects directly in tumor cells, providing an assay that accounts for cell-specific criteria that influence sensitivity such as different tubulin isotypes, tubulin mutations, drug metabolism, and efflux mechanisms.