Induction of acid and oxidative reistance in Escherichia cole 0157:H7 by exposure to short-chain fatty acids

Abstract

Short-chain fatty acids (SCFAs) are commonly used as food preservatives to prevent microbial contamination of meat carcasses. However, the food-borne pathogen, E. coli O157:H7, is more resistant than other E. coli strains to SCFA treatment. Furthermore, those cells that survive SCFA treatment may be better able to survive stress conditions encountered by E. coli O157:H7 in food products and/or its mammalian hosts. I hypothesize that SCFAs encountered by E. coli O157:H7 during its life cycle play a significant role in enhancing its virulence by (1) boosting its resistance to environmental stresses and/or (2) altering the expression of its virulence genes. Exposure to acetate, propionate, butyrate, or a mixture of all three SCFAs enhanced the resistance of both E. coli K-12 and E. coli O157:H7 to acid shock. Adaptation to acetate enhanced the resistance of E. coli O157:H7 to oxidative stress, but did not alter its resistance to heat shock. The SCFA-mediated acid resistance observed in E. coli K-12 and E. coli O157:H7 was dependent on new protein synthesis. The nature and extent of the molecular response of E. coli O157:H7 to SCFAs was characterized via two-dimensional gel electrophoresis and gene array analysis. The identity of proteins induced by SCFAs in E. coli O157:H7 and their potential role(s) in mediating acid and oxidative resistance remain to be determined.