Lactic streptococcal agglutinins Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/n583xz12g

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  • Lactic streptococcal agglutinins are known to promote settling of starter bacteria in milk, resulting in spongy, mealy, shattered curd and sludge formation defects in cottage cheese. These agglutinins are natural antibodies secreted by lactating cows in mature milk in response to infections (mastitis) and in colostrum milk as protective antibodies for newborn calves. The starter bacteria act as particulate antigens and form lattice-like complexes with the agglutinins and sediment to the bottom of milk vats, depriving upper milk layers from lactic acid production. A simple rapid screening test (Rose-bengal-stained antigen plate test) was developed to detect the presence of these natural antibodies in milk Trismaleate buffer at pH 7.0 with a high molarity (0.5 M) was selected as the most appropriate antigen-suspending solution. Two percent packed streptococcal cell volumes (PCV) were found to yield best results with all tested lactic streptococcal stained antigens. Each of 3%, 4% and 5% stain concentrations gave results of easy color readability. No totally agglutinin-resistant lactic streptococcal strains were found in testing colostrum whey samples. However, less agglutinin-susceptible strains such as S. lactis C₂ were detected by the test. The specificity of the agglutinins was studied by immuno-fluorescent assays, revealing a high specificity of starter bacteria for the IgG immunoglobulins. Moreover, less specificity was seen with IgM immunoglobulins. The agglutination behaviour of starter bacteria in milk was followed through a pH measurement profile at three different vertical locations. Agitation of milk with hgigh agglutination titers for 75 minutes did not alter settling of starter bacteria. Nevertheless, the pattern of settling was distrubed with lower agglutinin titers. Autoclaving the milk before mixing with unheated agglutinin-containing whey samples, dramatically reduced the agglutination reaction. The Rose bengal-stained plate antigen test results proved to be comparable with immunofluorescent studies and the studied starter agglutination reactions. Some evidence for seasonal occurrence of cheese starter agglutation was acquired from the results of the different studies. Studies also were made to explore the possible usefulness of the milk ring test for detecting the presence of lactic streptococcal agglutinins in milk.
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