Serological Identification of Propionibacteria in Milk and Cheese Samples

A serological method of agglutination was developed to allow rapid identification of propionibacteria isolated from dairy products. Antisera were obtained by immunizing rabbits with 17 strains belonging to the 4 main species most frequently encountered in dairy products. It was shown that antisera raised against P. freudenreichii do not cross react with either P. jensenii, P, acidi propionici or P. thoenii. Low cross reactivities observed between the last 3 species could be avoided by using absorbed or adequately diluted antisera. Analyses performed on Swiss dairy products have shown that P. freudenreichii was almost exclusively identified in milk and cheese. P. thoenii was found only in some cheeses suffering from the fault known as 'red spotting'; P. acidi propionici and P. jensenii were practically non existent.