Submitted to: Conference on Rumen Function
Publication Type: Abstract Only
Publication Acceptance Date: 11/14/2000
Publication Date: 11/14/2000
Citation: JARVIS, G.N., RUSSELL, J.B. THE EXTREME ACID RESISTANCE OF ESCHERICHIA COLI IS REGULATED BY AMINO ACID AVAILABILITY AS WELL AS VOLATILE FATTY ACIDS. CONFERENCE ON RUMEN FUNCTION. 2000.
Technical Abstract: Many bacteria are killed by the low pH of the gastric stomach, but Escherichia coli has an inducible mechanism of extreme acid resistance that can overcome this barrier. Previous work showed that the extreme acid resistance of E. coli could be induced by undissociated acids, but genetic studies indicated that amino acid decarboxylases are also involved. When a afreshly isolated E. coli strain and O157:H7 were grown anaerobically on maltose with less than 0.25 mg/ml yeast extract or Trypticase, the acid shock (pH 2.0, 1 h) survival was less than 0.01%, but acetate (50 mM, pH 7.0) increased the survival 1000-fold. If cultures were supplemented with 1.5 mg/ml Trypticase, the acid shock survival was already so high (approximately 50%) that they no longer responded to acetate. When the strains were grown aerobically in LB (a common laboratory medium based on amino acids), acid shock survivals were nearly 100%. Stationary phase cells were 100-fold more resistant to acid shock than those growing exponentially, but refrigeration (7days, 5s C) did not trigger an increase in acid resistance. These results support the idea that the acid resistance of E. coli is regulated by amino acid availability as well as volatile fatty acids, but it is unlikely that high concentrations of amino acids would ever be available in the GI tract.