Internal pH and Acid Anion Accumulation in and Exposed to Lactic or Acetic Acids at Mildly Acidic pH.

Organic acids are widely employed in the food industry to control growth of microbial pathogens such as and There is substantial evidence that intracellular accumulation of acid anions is a major inhibitor to cell viability, and that some bacteria are able to combat the toxic effects of anion accumulation their ability to continue active metabolism at a lower intracellular pH (pH). This study followed the accumulation of acid anion into the cell pellet and parallel changes in pH in two human pathogenic strains of (N1-227 and R2-499) and in O157:H7 after exposure to sub-bacteriostatic levels of lactic and acetic acids at mildly acidic pH 6. The methodology employed in these studies included independent measures of pH and intracellular anion accumulation.

Organic Acid Exposure Enhances Virulence in Some Strains Using the Infection Model.

Prior research has suggested that the use of organic acids in the food industry may unintentionally enhance pathogenicity of strain N1-227 and R2-499. This study explored the connection between habituation to L-lactic acid or acetic acid and virulence in strains N1-227 and R2-499 using selected gene expression analysis and the wax worm model for infection. Expression of transcription factors ( and ) and genes related to acid resistance (, and ) and bile resistance ( and ) or to virulence (, and ) was investigated by quantitative real-time PCR (qRT-PCR), while virulence was assessed by following the lethal time to 50% population mortality (LT) of larvae after injection of untreated and habituated Twenty minutes of habituation to the organic acids at pH 6.

Effect of oxygen concentration in modified atmosphere packaging on color changes of the M. longissimus thoraces et lumborum from dark cutting beef carcasses.

The objective of this study was to investigate the effect of modified atmosphere packaging (MAP) with different oxygen concentrations on color changes of dark-cutting beef steaks from M. longissimus thoraces et lumborum. Four normal-pH (mean pH = 5.

Habituation to organic acid anions induces resistance to acid and bile in Listeria monocytogenes.

We evaluated the intrinsic and inducible resistance of four human pathogenic strains of Listeria monocytogenes to acid and bile, factors associated with virulence. Cells were grown in media at pH 7.4, or in media at pH 6.

Color and thiobarbituric acid values of cooked top sirloin steaks packaged in modified atmospheres of 80% oxygen, or 0.4% carbon monoxide, or vacuum.

Case-ready fresh beef is typically packaged in a modified-atmosphere with approximately 80% oxygen and 20% carbon dioxide. Recently, USDA approved distribution of fresh meats in a master bag system using 0.4% carbon monoxide (CO).