Immediate Reduction of Salmonella enterica Serotype Typhimurium Viability via Membrane Destabilization following Exposure to Multiple-Hurdle Treatments with Heated, Acidified Organic Acid Salt Solutions

Abstract

The antimicrobial activity of organic acids in combination with nonchemical treatments was evaluated for inactivation of Salmonella enterica serotype Typhimurium within 1 min. It was observed that the effectiveness of the multiple-hurdle treatments was temperature (P < 0.05) and pH (P < 0.05) dependent and corresponded to the degree of organic acid lipophilicity (sodium acetate being least effective and sodium propionate being the most effective). This led to the hypothesis that the loss in viability was due at least in part to cell membrane disruption. Evaluation of osmotic response, potassium ion leakage, and transmission electron micrographs confirmed treatment effects on the cell membrane. Interestingly, all treatments, even those with no effect on viability, such as with sodium acetate, resulted in measurable cellular stress. Microarray experiments explored the specific response of S. Typhimurium to sodium acetate and sodium propionate, the most similar of the tested treatments in terms of pK a and ionic strength, and found little difference in the changes in gene expression following exposure to either, despite their very different effects on viability. Taken together, the results reported support our hypothesis that treatment with heated, acidified, organic acid salt solutions for 1 min causes loss of S. Typhimurium viability at least in part by membrane damage and that the degree of effectiveness can be correlated with lipophilicity of the organic acid. Overall, the data presented here indicate that a combined thermal, acidified sodium propionate treatment can provide an effective antimicrobial treatment against Salmonella.

Salmonella Pathogenicity and Host Adaptation in Chicken-Associated Serovars

“…Responses were dependent on the type of acid used and were time dependent, with hilA being upregulated after a 2-h exposure to the respective acid (350). When Milillo et al compared S. Typhimurium transcriptome responses to sodium acetate and sodium propionate exposure after 1 min (55°C at pH 4.0), the respective gene expression patterns were similar, with no increases in expression levels of rpoS, phoPQ, or virulence factors despite their established roles in organic and inorganic acid stress (35,327,328,338). Conversely, genes related to attachment and/or motility functions were induced, which has been observed previously for S. Typhimurium attachment genes after exposure to 42°C (351).…”

“…Other stress combinations appear to have more of an impact on SCFA inhibition of Salmonella. Milillo and coworkers demonstrated not only that the combination of heat (50°C to 60°C) and organic acids was more effective than single intervention applications when applied to S. Typhimurium but also that heated acidified solutions caused substantial membrane damage and leakage of intracellular ions (338,339). There may also be potential serovar differences.…”

Impairment of Swimming Motility by Antidiarrheic Lactobacillus acidophilus Strain LB Retards Internalization of Salmonella enterica Serovar Typhimurium within Human Enterocyte-Like Cells

“…10C). The antidiarrheal drug Lactéol Fort includes a lyophilized heatinactivated culture of L. acidophilus strain LB that contains lactic acid, and a heated and acidified, but not a nonheated, lactic acid solution destabilized membranes and promoted potassium leakage in stationary-phase S. Typhimurium (38). Experiments to determine whether or not the heated (110°C) MRS broth containing lactic acid modified the swimming of exponential-phase S. Typhimurium SL1344 showed that treatment with heated lactic acid at 50 or 100 mM did not modify S. Typhimurium SL1344 motility whereas treatment with a concentration of 200 mM resulted in a 2-fold increase in inhibitory activity compared with nonheated lactic acid results (not shown).…”

Growth of healthy and sanitizer-injured Salmonella cells on mung bean sprouts in different commercial enrichment broths

“…The antimicrobial effect of organic acids appears to be the result of lipophilic, undissociated acids permeating the plasma membrane, resulting in cell death (Adams and Hall, 1988;Milillo et al, 2011). PMA treatment prior to real-time PCR allows for distinction of viable from dead cells by binding to DNA of dead cells and preventing amplification of the PCR target sequence.…”