The ability of Escherichia coli O157:H7 to decrease its intracellular pH and resist the toxicity of acetic acid

Abstract

Batch cultures of Escherichia coli K-12 grew well in an anaerobic glucose medium a t pH 5.9, but even small amounts of acetate (20 mM) inhibited growth and fermentation. E. coli 0157: H7 was a t least fourfold more resistant to acetate than K-12. Continuous cultures of E. coli K-12 (pH 5.9, dilution rate 0085 h'l) did not wash out until the sodium acetate concentration in the input medium was 80 mM, whereas E. coli 01 57 : H7 persisted until the sodium acetate concentration was 160 mM. E. coli K-12 cells accumulated as much as 500 mM acetate, but the intracellular acetate concentration of 01 57 : H7 was never greater than 300 mM. Differences in acetate accumulation could be explained by intracellular pH and the transmembrane pH gradient (ApH). E. coli K-12 maintained a more or less constant ApH (intracellular pH 68), but E. coli 0157:H7 let its ApH decrease from 0.9 to 0.2 units as sodium acetate was added to the medium. Sodium acetate increased the rate of glucose consumption, but there was little evidence to support the idea that acetate was creating a futile cycle of protons. Increases in glucose consumption rate could be explained by increases in D-lactate production and decreases in ATP production. lntracellular acetate was initially lower than the amount predicted by ApH, but intracellular acetate and ApH were in equilibrium when the external acetate concentrations were high. Based on these results, the acetate tolerance of 0157: H7 can be explained by fundamental differences in metabolism and intracellular pH regulation. By decreasing the intracellular pH and producing large amounts of D-lactate, 0157:H7 is able to decrease ApH and prevent toxic accumulations of intracellular acetate anion.

Effect of Lactobacillus sp. isolates supernatant on Escherichia coli O157:H7 enhances the role of organic acids production as a factor for pathogen control

“…Indeed, it is well known that most of the antagonistic effects of Lactobacillus on E. coli growth could be due to the presence of organic acids that are produced during cell growth (Axe & Bailey 1995, Diez-Gonzalez & Russell 1997). …”

“…The authors reported that lactic acid exerts greater inhibitory effects on the growth of the pathogenic bacteria than acetic acid and propionic acid; however, the combination of the organic acids exhibited an important synergic effect in the inhibition of this pathogen (Cheng et al 2003, Varalakshmi et al 2013). According to Diez-Gonzalez & Russell (1997) small amounts of sodium acetate (1.6g. L -1 ) can inhibit the growth of E. coli O157:H7.…”

“…The non-dissociated forms of organic acids are able to function as protonophores, inducing the acidification of the cytoplasm and the accumulation of toxic anions. The decrease in the cell's internal pH affects the influx of protons through the cell membrane, which dissipates the proton-motive force, reducing cellular energy (ATP) and affecting substrate uptake in the cell (Axe & Bailey 1995, Diez-Gonzalez & Russell 1997 (Poppi et al 2008, Servin & Coconnier 2003, Kalantzopoulos 1997, Jin et al 1996. In spite of many detailed studies concerning the antagonistic effects of these bacteria on pathogens, there is still a need for new bacterial strains with antimicrobial properties for clinical and commercial benefits (Chaucheyras-Durand & Durand 2010).…”

Effect of Forage or Grain Diets with or without Monensin on Ruminal Persistence and Fecal Escherichia coli O157:H7 in Cattle

“…Diets high in grain generate high VFA concentrations and low pH, creating a less conducive environment for E. coli O157:H7, whereas lower VFA concentrations and higher pH in forage-fed cattle may be more hospitable for the growth and survival of the organism (31,32). It is known that E. coli O157:H7 is acid resistant and grows better under acidic conditions than other strains of E. coli (10). However, Tkalcic et al (35) reported no difference in ruminal persistence or fecal E. coli O157:H7 in calves fed the high-roughage or high-concentrate diet, although ruminal pH and VFA concentrations differed between the diets.…”

The potential for the control ofEscherichia coliO157 in farm animals

“…Diez-Gonzalez and Russell (1997) suggested that a strain of E. coli 0157 was more tolerant of high concentrations of acetate at pH 5·9 than was E. coli strain K-12. The strains were grown anaerobically at a very slow growth rate in a chemostat and the yield measured.…”