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 (IC(50) 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 mu g 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.