Development of a Cross-Reactive Monoclonal Antibody to Sulfonamide Antibiotics: Evidence for Structural Conformation-Selective Hapten Recognition

Production of generic monoclonal antibody and development of chemiluminescence immunoassay for determination of 32 sulfonamides in chicken muscle

A hapten of sulfabenzamide was first synthesized to generate a monoclonal antibody that simultaneously recognized 32 sulfonamides. The computational simulation showed that the 3D conformation, molecular bend angle, molecular volume, electronic charge of core structure of these drugs all showed influences on the antibody binding. The antibody was combined with a heterologous enzyme-labeled hapten to develop a direct competitive chemiluminescence enzyme linked immunosorbent assay for determination of the 32 sulfonamides in chicken muscle sample. The CRs of the optimized method for these drugs were in the range of 7.3%-1778%, and the IC₅₀ values were in the range of 0.038-11.2 ng/g. The limits of detection for detection of these drugs in chicken were in the range of 0.03-26 ng/g. Their recoveries from the standards fortified blank chicken samples were in the range of 60.8%-97.1%. Therefore, this method could be used as a useful tool for routine screening sulfonamides residues in meat.

A Class-Selective Immunoassay for Sulfonamides Residue Detection in Milk Using a Superior Polyclonal Antibody with Broad Specificity and Highly Uniform Affinity

The development of multianalyte immunoassays with an emphasis on food safety has attracted increasing interest, due to its high target throughput, short detection time, reduced sample consumption, and low overall cost. In this study, a superior polyclonal antibody (pAb) against sulfonamides (SAs) was raised by using a bioconjugate of bovine serum albumin with a rationally designed hapten 4-[(4-aminophenyl) sulfonyl-amino]-2-methoxybenzoic acid (SA10-X). The results showed that the pAb could recognize 19 SAs with 50% inhibition (IC₅₀) below 100 µg L^-1 and a recognition profile for SAs containing, either a five-atom ring or a six-atom ring, with highly uniform affinity. A three-dimensional quantitative structure-activity relationship analysis indicated that the electrostatic features of SAs play a considerably important role, during recognition with pAb than stereochemical effects. Skimmed milk samples were directly diluted five times before analysis. After optimization, the limit of detection for sulfamonomethoxine, sulfamethoxazole, sulfaquinoxaline, sulfadimethoxine, and sulfamethazine were 1.00, 1.25, 2.95, 3.35, and 6.10 µg L^-1, respectively. The average recoveries for these 5 SAs were 72.0⁻107.5% with coefficients of variation less than 14.1%. The established method, based on pAb, with broad specificity and uniform affinity, offered a simple, sensitive, and high-throughput screening tool for the detection of multi-SAs in milk samples.

Novel hapten synthesis for antibody production and development of an enzyme-linked immunosorbent assay for determination of furaltadone metabolite 3-amino-5-morpholinomethyl-2-oxazolidinone (AMOZ)

A heterologous competitive indirect enzyme-linked immunosorbent assay (ciELISA) for the determination of the furaltadone metabolite 3-amino-5-morpholinomethyl-2-oxazolidinone (AMOZ) was developed. AMOZ was derivatised with 2-(4-formylphenoxy) acetic acid or 2-(3-formylphenoxy) acetic acid to obtain two novel immunizing haptens. The ability of these haptens in producing specific polyclonal antibodies against the nitrophenyl derivative of AMOZ (NPAMOZ) was compared with that of traditional immunizing haptens (derivatised AMOZ with 3-carboxybenzaldehyle or 4-carboxybenzaldehyle). The results indicated that the novel immunizing haptens were able to produce antibodies with almost a two-fold improvement in sensitivity of the ciELISA for NPAMOZ in comparison with the existing antibody based ELISAs. The differences in sensitivity were explained by the molecular modeling of the lowest energy conformations of NPAMOZ and the haptens. Another novel hapten, derivatised AMOZ with 2-oxoacetic acid, was synthesized and used as a heterologous coating hapten. The results showed that this strategy of using only a partial structure of the target molecule as the coating hapten was able to obtain a two to three-fold improvement in sensitivity. This study provided a modern approach for the development of an immunoassay with improved sensitivity for the metabolites of nitrofuran antibiotics.

Triacetone triperoxide (TATP): hapten design and development of antibodies

Triacetone triperoxide (TATP), an improvised explosive, is a potential security threat because of its cost-efficient synthesis and the difficulty in detecting it. A highly selective antibody could provide the necessary specificity to the detection process. To obtain antibodies, a hapten made from acetone, hydrogen peroxide, and 7-oxooctanoic acid has been designed, synthesized, and confirmed by NMR that displays the utmost similarity to the analyte. The single-crystal X-ray structures of the solvated species TATP·methanol (1:1) and the TATP derivate were determined. In both compounds, the molecules exhibit D(3) symmetry and adopt a twisted boat-chair conformation. The hapten was coupled to bovine serum albumin, and mice were immunized. An immune response against TATP was elicited, and selective antibodies were detected in the mouse serum, which should be very useful for the development of a TATP biosensor system. An ELISA with a limit of detection for TATP of 65 μg L(-1) is shown.

Review on enzyme-linked immunosorbent assays for sulfonamide residues in edible animal products

The current status of enzyme-linked immunosorbent assays (ELISAs) for sulfonamides in edible animal products is reviewed. The attention was focused on the design and synthesis of haptens, conjugation to carrier protein, production of antibody, application of homologous and heterologous systems, as well as the molecular modeling of the haptens and sulfonamides. Researches have shown that sulfonamides seem to be particularly resistant to attempts to produce broad specificity antibodies. By summarizing the available research on sulfonamide ELISAs, it is hoped that it can be considered as a basis for further investigation aimed at developing the most efficient approaches for detection.

Development of flow-through and dip-stick immunoassays for screening of sulfonamide residues

Two formats of membrane-based competitive enzyme immunoassays (flow-through and dip-stick) have been developed for the screening of sulfonamide residues in pig muscle and milk. Membrane was coated with anti-sulfonamide antibody and a sulfonamide hapten D2-horseradish peroxidase (HRP) conjugant was used as the labeled antigen for competitive assay of sulfonamides. Visual detection limits of the flow-through or dip-stick assay were 1-5 microg L(-1) or 1-10 microg L(-1) in buffer for seven sulfonamides, respectively. Assay validation was performed using samples spiked with single sulfonamide, spiked samples were tested using the developed strip assays and results were compared with those obtained by a validated high-performance liquid chromatograph (HPLC) method. Results showed that the two strip assays were correlated well with HPLC, respectively. With assay times of 5 min (flow-through) and 15 min (dip-stick), these rapid tests could offer simple, rapid and cost-effective on-site screening tools to detect sulfonamides in pig muscle (flow-through or dip-stick) or milk (only dip-stick).

Rapid enzyme-linked immunosorbent assay and colloidal gold immunoassay for kanamycin and tobramycin in Swine tissues

A monoclonal antibody (Mab) was produced by using the kanamycin-glutaraldehyde-bovine serum albumin (Kan-GDA-BSA) conjugate as the immunogen. The anti-Kan Mab exhibited high cross-reactivity with tobramycin (Tob) and slight or negligible cross-reactivity with other aminoglycosides. The specificity and cross-reactivity of this Mab are discussed regarding the three-dimensional, computer-generated molecular models of the aminoglycosides. Using this Mab, a rapid enzyme-linked immunosorbent assay (ELISA) and a colloidal gold-based strip test for Kan and Tob were developed. The rapid ELISA showed a 50% inhibition value (IC 50) of 0.83 ng/mL for Kan and 0.89 ng/mL for Tob with the analysis time less than 40 min, and the recoveries from spiked swine tissues at levels of 25-200 microg/kg ranged from 52% to 96% for Kan and 61% to 86% for Tob. In contrast, the strip test for Kan or Tob had a visual detection limit of 5 ng/mL in PBS, 50 microg/kg in meat or liver, and 100 microg/kg in kidney, and the results can be judged within 5-10 min. Observed positive samples judged by the strip test can be further quantitated by ELISA, hence the two assays can complement each other for rapid detection of residual Kan and Tob in swine tissues. Moreover, physical-chemical factors that affected the ELISA and strip test performance were also investigated. The effect of pH and antibody amount for gold-antibody conjugation on the strip test sensitivity was determined followed by a theoretical explanation of the effects.

Monoclonal antibody-based fluorescence polarization immunoassay for sulfamethoxypyridazine and sulfachloropyridazine

In this paper, a new monoclonal antibody (Mab) against sulfamethoxypyridazine (SMP) was produced, and a fluorescence polarization immunoassay (FPIA) based on the produced Mab was developed and optimized for the qualitative screening analysis of SMP. The Mab was raised from mice immunized with SMP linked to bovine serum albumin (BSA) by carbodiimide activated ester formation, using a succinic anhydride spacer molecule between SMP and BSA. Fluorescein labeled sulfachloropyridazine (SCP) and SMP (tracer) were synthesized and purified by thin layer chromatography (TLC). The developed screening FPIA method can tolerate up to 20% methanol, and satisfactory assay sensitivity can be obtained between pH 4 and pH 8 and at lower salt concentration. The anti-SMP Mab exhibited a high cross-reactivity with SCP. The effect of the tracer structure on the analytical characteristic of the determination and on antigen-antibody binding constants was studied. The limits of detection (LOD) were 0.7 ng/mL for SMP and 0.25 ng/mL for SCP in buffer, respectively, whereas negligible cross-reactivities were exhibited by related sulfonamides. Analysis of SMP and SCP-fortified milk samples by the FPIA showed average recoveries from 60 to 145%.

Development of a monoclonal antibody-based broad-specificity ELISA for fluoroquinolone antibiotics in foods and molecular modeling studies of cross-reactive compounds

A competitive indirect enzyme-linked immunosorbent assay (ciELISA) using monoclonal antibodies (Mabs) having broad specificity for fluoroquinolone (FQ) antibiotics is described. Four FQs, ciprofloxacin (CIP), enrofloxacin (ENR), norfloxacin (NOR), and ofloxacin (OFL), were conjugated to bovine serum albumin for immunogens and to ovalbumin for coating antigens. A Mab C4A9H1 raised against the CIP hapten exhibited high cross-reactivity (35-100%) with 12 of 14 FQs and detected these FQs in a ciELISA below their maximum residue levels (MRLs) with good sensitivity at 50% binding inhibition (IC50). The quantitative structure-activity relationship (QSAR) between Mab C4A9H1 and various FQs by comparative molecular field analysis (CoMFA) showed a high predictive ability with a cross-validation q2 value of 0.866. Using a simple purification process and the broad-specificity ciELISA adapted for analysis of FQs in chicken muscle, chicken liver, honey, shrimp, and whole egg samples demonstrated recoveries of 60-93% for CIP, ENR, NOR, OFL, flumequine, and danofloxacin.

Development of an enzyme-linked immunosorbent assay for seven sulfonamide residues and investigation of matrix effects from different food samples

Direct competitive enzyme-linked immunosorbent assays (ELISA) were developed to detect a broad range of sulfonamides in various matrices. Screening for this class of antibiotics in pig muscle, chicken muscle, fish, and egg extracts was accomplished by simple, rapid extraction methods carried out with only phosphate-buffered saline (PBS) buffer. Twenty milliliters of extract solution was added to 4 g of sample to extract the sulfonamide residues, and sample extracts diluted with assay buffer were directly analyzed by ELISA; matrix effects could be avoided with 1:5 dilution of pig muscle, chicken muscle, and egg extracts with PBS and 1:5 dilution of fish extract with 1% bovine serum albumin (BSA)-PBS. For liver sample, the extraction method was a little more complicated; 2 g of sample was added to 20 mL of ethanol, mixed, and then centrifuged. The solvent of 10 mL of the upper liquid was removed, and the residues were dissolved in 10 mL of PBS and then filtered; the filtrate was diluted two-fold with 0.5% BSA-PBS for ELISA. These common methods were able to detect seven sulfonamide residues such as sulfisozole, sulfathiazole, sufameter, sulfamethoxypyridazine, sulfapyridine, sulfamethizole, and sulfachlorpyridazine in pig muscle, liver, chicken muscle, egg, and fish. The assay's detection limits for these compounds were less than 100 microg kg-1. Various extraction methods were tested, and the average recovery (n=3) of 100 microg kg-1 for the matrices was found to range from 77.3 to 123.7%.

Development of an immunochromatographic lateral-flow test strip for rapid detection of sulfonamides in eggs and chicken muscles

A rapid immunochromatographic lateral-flow test strip was developed in the competitive reaction format for the detection of sulfonamides in eggs and chicken muscle. A monoclonal antibody against the common structure of sulfonamides was conjugated to colloidal gold particles as the detection reagent and an N-sulfanilyl-4-aminobenzoic acid (SUL)-bovine serum albumin (BSA) conjugate was immobilized to a nitrocellulose membrane as the capture reagent to prepare the test strip. With this method, it required only 15 min to accomplish the semiquantitative or quantitative detection of sulfonamides. The sensitivity to sulfonamides (sulfamonomethoxine, sulfamethoxydiazine, sulfadimethoxine, and sulfadiazine) was at least 10 ng/mL, as determined with an optical density scanner. By eye measurement, the sensitivity was 20 ng/mL for sulfamonomethoxine, sulfamethoxydiazine, and sulfadimethoxine and 40 ng/mL for sulfadiazine. On the basis of a sulfamonomethoxine standard curve, recoveries were from 89.5 to 95.6% for sulfamonomethoxine, from 89.5 to 95.1% for sulfamethoxydiazine, from 85.0 to 95.6% for sulfadimethoxine, and from 44.8 to 60.9% for sulfadiazine in egg and chicken muscle samples. A parallel analysis of 27 egg samples and 28 chicken muscle samples from the animal experiment showed that the differences between test strips and high-performance liquid chromatography (HPLC) were from 0.8 to 11.2% for egg samples and from 2.2 to 34% for chicken muscle samples for the quantitative detection, and the agreement rates between test strips and HPLC were 100%, based on the maximum allowed residue level of sulfadiazine (100 ng/g) established by the European Union and China. In conclusion, the method is rapid and accurate for the detection of sulfonamides in eggs and chicken muscles.

Hapten synthesis and development of polyclonal antibody-based multi-sulfonamide immunoassays

This paper reports the synthesis of five sulfonamide derivatives, the production of broad-specificity polyclonal antibodies for immunoassay of sulfonamides, and the analysis of milk samples by developed assay. The three-step synthesis procedure reported in most of the literature was adopted and modified in this study. In the procedure, the purification of the intermediate was avoided and the time of synthesis was shortened from >20 to 6-9 h with improved yields. This method is generally applicable to the synthesis of haptens containing the common structure of sulfonamides. Three haptens were coupled to keyhole limpet hemocyanin, and polyclonal antibodies were obtained from rabbits immunized with these conjugates. Using the antibodies obtained, from one of these was developed an enzyme-linked immunosorbent assay (ELISA) based on the competition between free sulfonamides and the hapten-horseradish peroxidase (HRP) conjugates. The hapten-HRP conjugate giving the best competitive results and 11 structurally different sulfonamides showed 50% inhibition at concentrations of <100 ng mL(-1). After removal of the protein with acetone, milk samples were analyzed by ELISA directly; a matrix effect could be avoided when a 1:20 dilution with phosphate-buffered saline was used, and 104-131% recoveries of spiked samples were obtained. The developed immunoassay is suitable to determine sulfisozole, sulfathiazole, sulfameter, sulfamethoxypyridazine, sulfapyridine, and sulfamethizole below the maximum residue limit in milk (100 ng mL(-1) of total sulfonamides) rapidly and reliably.

Analysis of sulphonamide residues in edible animal products: A review

The methods of analysis for sulphonamide residues in edible animal products are reviewed. Sulphonamides are widely used for therapeutic and prophylactic purposes in both humans and animals, sometimes as growth promoters as additives in animal feed. As a result of their widespread use, there is concern about whether the levels used of these drugs can generate serious problems in human health, e.g., allergic or toxic reactions. Several methods for the determination of sulphonamides have been reported in the literature and this review considers high-performance liquid chromatography (HPLC), liquid chromatography-mass spectrometry (LC/MS), gas chromatography (GC), thin-layer chromatography (TLC), high-performance capillary electrophoresis (HPCE), enzyme-linked immunosorbant assay (ELISA), biosensor immunoassay (BIA) and microbiological methods. Specific aspects of analysing sulphonamides, such as sample handling, chromatographic conditions and detection methods are discussed. Methods for drug residue monitoring should be accurate, simple, economical in both time and cost, and capable of detecting residues below the maximum residue limits (MRL). The current sulphonamide detection technologies are based on chromatographic methods or bacteriological growth inhibition. The instrumental methods such as HPLC and GC are both sensitive and specific, but are laborious and expensive. Because of the labour-intensive processes, only a few cases of GC methods applied to residue analysis have been published. These methods are suitable for confirmation but not for screening of large numbers of samples. Microbiological methods do not require highly specialized and expensive equipment. They also use highly homogeneous cell populations for testing and thus result in better assay precision. Although HPCE has powerful separation ability, the precision is poor and the instrument still needs to be improved. To date, this technique has not been widely applied to routine analysis. Currently, TLC has been almost replaced by other instrumental analysis. A rapid, sensitive and specific assay is required to detect positive samples in routine analysis, which can then be confirmed for the presence of sulphonamides by HPLC. Immunochemical methods such as ELISA can be simple, rapid and cost-effective, with enough sensitivity and specificity to detect small molecules. This review can be considered as a basis for further research aimed at identifying the most efficient approaches.

Broad-Specificity Immunoassays for Sulfonamide Detection: Immunochemical Strategy for Generic Antibodies and Competitors

Development of antibodies with broad specificity recognition for sulfonamide drugs was found to be surprisingly difficult when conventional immunochemical strategies were applied to hapten design. To improve the cross-reactivity pattern of antibodies for the family of sulfonamide drugs, a novel strategy based on the single-ring (fragment-derived) hapten moieties with different spacer substituent lengths was employed for the preparation of immunogens, coating conjugates, and enzyme competitors. The rabbit antibodies raised against a common (one-ring) p-aminobenzenesulfonamide hapten moiety (attached to a carrier protein through the N-1 position) in combination with a homologous hapten-peroxidase tracer allowed the detection of 15 sulfonamide species at the maximum residue limit level using direct ELISA. The two-ring 6-(4-aminobenzensulfonylamino)hexanoic hapten mimics, previously reported in the literature as a weak generic antigen, generated surprisingly superior immune responses in rabbits. The antibodies raised against this two-ring hapten were capable of detecting at least 19 and 17 sulfonamides in a direct ELISA system at the regulatory level with sensitivities corresponding to 20 and 50% binding inhibition, respectively. A negligible cross-reaction with N4 metabolites makes it possible to measure responses of parent sulfonamides in the presence of their metabolized forms. In skimmed milk, the highest limit of detection (LOD) for sulfacetamide defined as 20% inhibition was 65.2 microg x L(-1) (IC20 value), whereas the additional 18 sulfonamides tested exhibited LODs in the range of 0.2-36.8 microg x L(-1). This sensitivity allows simple multisulfonamide tests to be established for use in the laboratory or on site.

Generic Lanthanide Fluoroimmunoassay for the Simultaneous Screening of 18 Sulfonamides Using an Engineered Antibody

Sulfa antibiotics (sulfonamides) are used in veterinary and human medicine for therapeutic and prophylactic purposes. Veterinary use can result in foodstuffs derived from animals being contaminated with residual sulfonamides. Current sulfonamide-screening methods (mainly based on bacterial growth inhibition) are slow and inaccurate, since sensitivities of bacteria to different sulfonamides vary a lot. Therefore, a rapid immunoassay that was able to detect at least 18 different sulfonamides at the MRL level (100 microg/kg) from food samples in a single reaction was developed. The assay was reproducible and adequately accurate for screening purposes. The presence of sulfonamide metabolites did not cause major assay interference. We also demonstrated reliable detection of sulfonamides from a panel of meat, milk, and serum samples with the assay.

Engineering of a broad specificity antibody for simultaneous detection of 13 sulfonamides at the maximum residue level

Sulfa antibiotics (sulfonamides) are a group of molecules sharing the p-aminobenzenesulfonamide moiety. Sulfonamides are used in veterinary and human medicine. Sometimes, the meat or milk of medicated animals is contaminated with residual sulfonamides. Current analytical methods for sulfonamides are unfit for screening of food, because they are either too laborious, insensitive, or specific for a few sulfa compounds only. A rapid immunoassay for detection of all sulfas in a single reaction would thus be useful. Previously, we used protein engineering to improve the broad specificity of sulfa antibody 27G3. In this study, we improved the best mutant of the previous studies with site-directed mutagenesis. The new mutants recognized different sulfonamides with affinities sufficient for detection of all 13 tested sulfonamides below the MRL level. We furthermore demonstrated the functionality of one mutant in some real sample matrices.

Generation of group-specific antibodies against sulfonamides

To develop a sulfonamide-specific ELISA, different attempts were made to obtain monoclonal antibodies specific for the common structure of sulfonamides. In a first approach, sulfanilamide was linked to albumins using glutaraldehyde or a succinimide ester as cross-linker. A weak immune response or none at all was induced after immunization of mice with those conjugates. High antibody titers were obtained with conjugates where sulfanilamide was linked to albumins or casein (azocasein) with a diazotation reaction. However, the antibodies were only highly specific for the bound sulfanilamide molecule. In a second approach, sulfonamide-protein conjugates were used in which the sulfonamide molecule is linked at its side chain, leaving the common structure of sulfonamides unchanged. Three sulfonamide derivatives (S, TS, and PS, previously described in the literature) containing a carboxyl group in their side chain were linked to proteins using a carbodiimide mediated reaction. Immunization with the S-conjugates led to high antibody titers, but the antibodies were only highly specific for the bound S-molecule. Group-specific antibodies were obtained after immunization with the PS- and TS-conjugates. It was described that immunization with PS-conjugates lead to the recognition of other sulfonamides (sulfamethazine, -merazine, -diazine, and -dimethoxine) that are not well recognized by antibodies induced after immunization with TS-conjugates. Therefore, we tried to guide the immune response in the direction of recognition of the common structure of sulfonamides by immunizing the animals alternately with PS- and TS-conjugates. The polyclonal antibodies of the mice indeed had a broader specificity, but the specificity of the monoclonals obtained after fusion experiments was not influenced. Immunization with TS-conjugates seemed sufficient to obtain sulfonamide-specific monoclonal antibodies. With the best monoclonal (mAb 3B5B10E3) two competitive inhibition (ci) ELISA's were developed: one coated with antigen and the other coated with the monoclonal antibody. Sulfadiazine, -dimethoxine, -thiazole, -pyridine, and -methoxazole were detected in both ELISA's at their MRL-value (100 ppb) in buffer solution. Sulfadiazine, sulfathiazole, and sulfamethoxazole could even be detected at 10 ppb.

Neamin as an immunogen for the development of a generic ELISA detecting gentamicin, kanamycin, and neomycin in milk

A broad-specific ELISA using one antibody preparation for the detection of gentamicin, kanamycin, and neomycin in milk is reported for the first time. For the immunization of rabbits, neamin was used as the generic hapten on the basis of the facts that it is a two-ring fragment of neomycin and, in shape and charge, it resembles parts of kanamycin and gentamicin. Neamin was linked to the preactivated carrier protein keyhole limpet hemocyanin by EDC coupling. The specificity and sensitivity of the polyclonal antibodies for the aminoglycoside antibiotics were tested in a competitive assay using homologous and heterologous conjugates coupled by various conjugation procedures as the ELISA solid phase. In contrast to the homologous assay recognizing only neomycin, the heterologous assay could be used for the detection of the whole subclass of deoxystreptamin antibiotics in buffer and raw milk. Gentamicin, kanamycin, and neomcyin were detected in artificially contaminated undiluted raw milk (without sample pretreatment) with 50% inhibition levels at 9, 21, and 113 ng mL(-)(1), respectively. Neomycin levels were also measured in milk samples obtained from a cow suffering from mastitis and treated with an antibiotic cocktail including neomycin. Levels below the EU maximum residue levels for deoxystreptamin antibiotics could readily be measured in this generic ELISA.

Further improvement of broad specificity hapten recognition with protein engineering

Sulfa-antibiotics (sulfonamides) are widely used in veterinary medicine. Meat and milk from treated animals can be contaminated with sulfa residues. Current sulfonamide assays are unfit for screening of food, because they are either too laborious, insensitive or specific for a few sulfa compounds only. An immunoassay for detection of all sulfas in a single reaction would be useful for screening. Previously we have improved the broad specificity sulfa binding of antibody 27G3 with random mutagenesis and phage display. In order to improve the properties of this antibody further, mutants from the previous study were recombined and more mutations introduced. These new libraries were enriched with phage display and several different mutant antibodies were isolated. The cross-reaction profile of the best mutant was better than that of the wild-type antibody and the mutants of the previous study: it was capable of binding 10 of the tested 13 sulfonamides within a narrow concentration range and also bound the rest of the sulfas 5- to 11-fold better than the mutants of the previous study.

Improving broad specificity hapten recognition with protein engineering

Sulfa antibiotics (sulfonamides) are derivatives of p-aminobenzenesulfonamide that are widely used in veterinary medicine. Foods derived from treated animals may be contaminated with these drugs. However, current immunobased sulfonamide detection methods are unfit for screening of products because they are either too insensitive or specific for a few compounds only. An immunoassay capable of detecting all sulfas in a single reaction would be ideal for screening. For development of a binder capable of binding all sulfas, a protein engineering approach was chosen and the properties of monoclonal antibody 27G3 were improved with mutagenesis followed by selection with phage display. Several different mutant antibodies were isolated. The cross-reaction profile of the best mutant antibody was significantly improved over that of the wild-type antibody: it was capable of binding 9 of the tested 13 sulfonamides within a narrow concentration range and also bound the rest of the sulfas, albeit within a wider concentration range.

Production, characterization, and cross-reactivity studies of monoclonal antibodies against the coccidiostat nicarbazin

A cELISA was developed for the coccidiostat nicarbazin. On the basis of previous computer-assisted molecular modeling studies, p-nitrosuccinanilic acid (PNA-S) was selected as a hapten to produce antibodies to 4,4'-dinitrocarbanilide (DNC), the active component of the coccidiostat nicarbazin. Synthesis is described for the hapten [p-nitro-cis-1,2-cyclohexanedicarboxanilic acid (PNA-C)] used in a BSA conjugate as a plate coating antigen. Monoclonal antibodies (Mabs) were isolated that compete with nicarbazin, having IgM(kappa) isotype. Because of the lack of water solubility of nicarbazin, N,N-dimethylformamide (DMF) (3%, v/v) and acetonitrile (ACN) (10%, v/v) were added to the assay buffer to achieve solubility of nicarbazin and related compounds. The Nic 6 Mabs had an IC(35) value for nicarbazin of 0.92 nmol/mL, with a limit of detection of 0.33 nmol/mL. Nic 6 exhibited high cross-reactivity for PNA-S and PNA-C, and 3-nitrophenol, 4-nitrophenol, and 1-(4-chlorophenyl)-3-(4-nitrophenyl) urea. However, Nic 6 had little or no cross-reactivity with 15 other related compounds.