Development of a Competitive Indirect ELISA for the Determination of Lincomycin in Milk, Eggs, and Honey

Polyclonal antibodies to lincomycin (LIN) were developed in rabbit as a result of immunization with BSA−LIN conjugate. Periodate oxidizing of hapten was the common step of both immunogen synthesis and preparation of conjugated antigens for coating plates (homologous and heterologous). Several ELISA variants on a base of the different antigens immobilized on polystyrene were compared. Heterology of solid-phase antigens was provided with relative hapten clindamycin (CLIN) and ethylene- or hexanediamine as spacer arm between hapten and carrier. The spacer insertion yielded no desirable effect, whereas gelatin−CLIN assay variant showed better test characteristics in comparison with the homologous one, although insignificant (IC50 was 9.15 vs 18.3 ng mL−1). The detection limits of the developed test, being estimated as 0.43 ng mL−1 (milk) and 0.65 ng mL−1 (eggs), were sufficient to measure maximum residue levels for LIN in examined matrices. This value for honey was 1.9 ng mL−1 (1.3 μg kg−1). The assay sensitivity was enough to dilute milk, egg, and honey samples by 10−100 times to minimize matrix effect. The examination of matrix effect and simple ways of its overcoming are detailed in the paper. The developed assay showed 111% cross-reactivity with CLIN; therefore, it is suitable for the determination of both lincosamides.