Inhibition of K99 Antigen Synthesis by L-Alanine Enterotoxigenic Escherichia coli

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Abstract
The effect of various culture media on K99 antigen production by enterotoxigenic E. coli strains of bovine origin was investigated by slide agglutination tests, enzyme-linked immunosorbent assays and in vitro attachment to intestinal villi. L-Alanine at concentrations higher than 0.7 g l-1 was responsible for the inhibition of K99 synthesis observed on media rich in amino acids. The increased inhibitory activity of L-alanine in glucose-rich media after autoclaving suggested the formation of inhibitory products via Maillard''s reaction. Of various L-alanine derivatives tested, only those that hydrolyzed to L-alanine were inhibitory. L-Alanine analogues were without effect and the addition of 10 mM cAMP did not overcome the repression of K99 biosynthesis by L-alanine. Enzymes involved in cell wall synthesis such as L-alanine racemase or D-alanyl-D-alanine synthetase were evidently unaffected by L-alanine.