Development of an immunochemical method to detect Lactobacillus kefir

Abstract

Kefir is a fermented milk elaborated with kefir grains. It constitutes an ecological systemcomposed by a protein-polysaccharide matrix on which a complex microbiota is naturallyimmobilized. The objective of this work was to develop an antibody-based method in orderto achieve a simple and rapid way to quantify Lactobacillus kefir in a complex environment.Rabbit antisera against isolated S-layer proteins from L. kefir and L. parakefir were obtained.Both antisera recognized the 21 strains of L. kefir and the three strains of L. parakefir analysedby dot-blot. By indirect ELISA, specific antiserum against L. kefir S-layer showed reactivityagainst pure cultures of both L. kefir and L. parakefir, but did not react with L. brevis cells.Competitive ELISA allowed quantification of L. kefir at concentrations ranging from 5/105 to108 bacteria ml1, but neither L. parakefir nor L. brevis pure cultures produced inhibition.Through this approach it was possible to detect 108 L. kefir ml1 in samples of milk fermentedfor 48 h at 208C with different kefir grains. Competitive ELISA developed in our laboratory is asuitable method to detect and quantify L. kefir in milk and in consequence it could be applied toanalyse the relationship between the composition of microflora and probiotic and technologicalcharacteristics of the products.