Effectiveness of organic acid mixtures on reducing or eliminating Escherichia coli O157:H7 inoculated in a laboratory culture medium, tryptic soy broth

This study investigated the antibacterial effects of acetic acid (AA), lactic acid (LA), malic acid (MA), and their mixtures against Escherichia coli O157:H7 in a laboratory medium, tryptic soy broth stored at 25 °C. Viable counts were determined by plating on tryptic soy agar and sorbitol MacConkey agar, and physiological and structural changes were assessed via transmission electron microscopy (TEM) and propidium iodide (PI) uptake assays. Organic acids showed dose-dependent reductions of E. coli O157:H7, with LA exhibiting the greater inactivation action than AA and MA. Among OA mixtures tested, AA + MA displayed the most potent lethality, with log-reductions of $$\ge$$ 5.44 within 24 h despite having a higher pH level (3.00) than LA + MA (2.81). TEM and PI uptake analyses confirmed that the resultantly enhanced lethality of AA + MA was associated with an increase in the cell membrane permeabilization.