Antimicrobial Effect of Citric, Acetic, Lactic Acids and Sodium Nitrite against Escherichia Coli in Tryptic Soy Broth

Abstract

Antimicrobial effect of organic acids against E. coli (EC₁ and EC₂) was studied in  tryptic soy broth (pH 5) adjusted to various concentrations 1, 2, 3, 4 or 6% of the citric,  acetic and lactic acid then incubated at 5, 20 and 37ºC during 96 hours. In the second study, the effect of sodium nitrite on the survival of E. coli cells was investigated at pHs (4.5 and 6).   ¶¶In the majority of the cases, the order of effectiveness of the organic acids was: citric >acetic > lactic¶.¶ At low temperature, 1 to 6% of lactic and acetic acid does not seem sufficient concentrations to influence cellular viability significantly. ¶ In contrast, addition of citric acid (3%) to TSB medium reduced E. coli from approximately 6.3 log CFU/ml to an undetectable number. Furthermore, antimicrobial effect of all organic acids increased with increasing the temperature of incubation. This study has confirmed that the lethal effect of sodium nitrite was much enhanced by low pH. Thus, the most bactericidal effect was obtained at pH = 4.5 and the concentrations NaNO₂ (0.4 or 0.6).

Key words: Escherichia coli, Antimicrobial effect, citric acid, acetic acid, lactic acid, sodium nitrite.