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A simple magneto immunofluorescence assay for quinolone family detection in 96-well microplate was developed and applied to milk and groundwater samples. Norfloxacin (NOR) conjugated to albumin (BSA) was immobilised on magnetic beads (MBs) in a first step. The strategy was based on an indirect competitive assay between free and immobilised quinolone for anti-quinolone IgG antibody. Then, a peroxidase tracer was added as developer reagent. The fluorescence responses at 440 and 540 nm - excitation and emission wavelengths, respectively – were obtained by adding o-phenylenediamine and peroxide hydrogen as peroxidase substrates. The fluorescence response was indirectly proportional to the concentration of quinolone in the sample. Ciprofloxacin was selected as model quinolone with cut-off and limit of detection (LOD) of 4 and 8 μg L−1, respectively. Bovine milk and groundwater blank samples were spiked with ciprofloxacin at 5, 25 and 50 µg L−1 obtaining good recoveries (90–100%) with coefficient variation lower than 20% in all cases, in concordance with the results obtained by applying a reference method. Therefore, the method developed would be applicable for the detection of quinolones in bovine milk from dairy farms and in groundwater from sites with intensive livestock activities.

A novel microbiological system in microtiter plates consisting of five bioassays is presented for the detection and classification of antibiotic residues in milk. The bioassays were optimized for the detection of beta-lactams (Bioassay B: Geobacillus stearothermophilus), macrolides (Bioassay M: Bacillus megaterium with fusidic acid), tetracyclines (Bioassay T: B. megaterium with chloramphenicol), quinolones (Bioassay Q: Bacillus licheniformis) and sulfamides (Bioassay QS: B. licheniformis with trimethoprim) at levels near the maximum residue limits (MRL). The response of each bioassay was interpreted visually (positive or negative) after 4-5.5h of incubation. The system detects and classifies beta-lactams (5 pg/l of amoxicillin, 4 pg/l of ampicillin, 36 pg/l of cloxacillin, 22 pg/l of amoxicillin, 3 pg/l of penicillin, 114 pg/l of cephalexin, 89pg/l of cefoperazone and 116 pg/l of ceftiofur), tetracyclines (98 pg/l of chlortetracycline, 92 pg/l of oxytetracycline and 88 pg/l of tetracycline), macrolides (33 pg/l of erythromycin, 44 pg/l of tilmicosin and 50 pg/l of tylosin), sulfonamides (76 pg/l of sulfadiazine, 85 pg/l of sulfadimethoxine, 77 pg/l of sulfamethoxazole and 87pg/l of sulfathiazole) and quinolones (94 pg/l of ciprofloxacin, 98 pg/l of enrofloxacin and 79 pg/l marbofloxacin). In addition, the specificity values were high for B, T, Q (99.4%), M (98.8%) and QS (98.1%) bioassays. The control of antibiotics through this system can contribute to improving the quality and safety of dairy products. Resumen Se presenta un novedoso sistema microbiológico en placas de microtitulación compuesto por 5 bioensayos para la detección y clasificación de residuos de antibióticos en leche. Los bioensayos fueron optimizados para la detección de betalactámicos (bioensayo B: Geobacillus stearothermophilus), macrólidos (bioensayo M: Bacillus megaterium con ácido fusídico), tetraciclinas (bioensayo T: Bacillus megaterium con cloranfenicol), quinolonas (bioensayo Q: Bacillus licheniformis) y sulfamidas (bioensayo QS: Bacillus licheniformis con trimetoprima), a niveles cercanos a los límites máximos de residuos (LMR). La respuesta de cada bioensayo se interpretó visualmente (positiva o negativa) después de 4 a 5,5 h de incubación. El sistema detecta y clasifica betalactámicos (5 pg/l de amoxicilina, 4 pg/l de ampicilina, 36 pg/l de cloxacilina, 22 pg/l de amoxicilina, 3 pg/l de penicilina, 114 pg/l de cefalexina, 89 pg/l de cefoperazona y 116 pg/l de ceftiofur), tetraciclinas (98 pg/l de clortetraciclina, 92 pg/l de oxitetraciclina y 88 pg/l de tetraciclina), macrólidos (33 pg/l de eritromicina, 44 pg/l de tilmi-cosina y 50 pg/l de tilosina), sulfamidas (76 pg/l de sulfadiacina, 85 pg/l de sulfadimetoxina, 77 pg/l de sulfametoxazol y 87 pg/l de sulfatiazol) y quinolonas (94 pg/l de ciprofloxacina, 98 pg/l de enrofloxacina y 79pg/l de marbofloxacina). Además, los valores de especificidad fueron altos para los bioensayos B, T, Q (99,4%), M (98,8%) y QS (98,1%). El control de residuos de antibióticos mediante este sistema puede contribuir a mejorar la calidad e inocuidad de los productos lácteos.

A fast and simple screening fluorescent method was developed and applied for detection of quinolones in groundwater samples. The experimental conditions for quinolone family detection in 96-well plates were acid media (pH = 4.85) from acetate buffer solution (0.1 mol L−1) and 5.8 × 10−3 mol L−1 of anionic surfactant sodium dodecyl sulfate (SDS) as micellar media at excitation and emission wavelengths of 280 and 450 nm, respectively. The developed method was validated to guarantee the quality of the results reported. Thus, the decision limit (CCα) of ciprofloxacin of 6.8 μg L−1, the most prescript quinolone in our country, was selected as the cut-off level to classify the water samples as ‘suspect’ or ‘negative’ referred to quinolone content. The method showed good recoveries ranging between 80 and 114% for 6.8 μg L−1 ciprofloxacin with relative standard deviation values lower than 13%. Moreover, other families of antibiotics such as aminoglycoside, penicillin, macrolide, sulfonamide and tetracycline did not present interference in the quinolone detection. Groundwater samples from Argentine regions with intensive livestock activities were analysed by this method, and the results had a good correlation with a reference method based on ultraperformance liquid chromatography coupled to mass spectrometry.