Purified Plant-Derived Phenolic Acids Inhibit Salmonella Typhimurium without Alteration of Microbiota in a Simulated Chicken Cecum Condition

Abstract

Salmonella enterica serovar Typhimurium (ST) remains a predominant zoonotic pathogen because of its colonization in poultry, survivability in the environment, and increasing antibiotic-resistance pattern. Plant-derived phenolics, gallic acid (GA), protocatechuic acid (PA), and vanillic acids (VA) have demonstrated antimicrobial activity in vitro; therefore, this study collected chicken cecal fluid and supplemented it with these phenolics to evaluate their potential for eliminating ST and mod-ulating the microbiota of complex environments. ST was quantified through plating, while micro-biome analysis was performed through pair-end 16S-rRNA gene sequencing. CFU/mL of ST in cecal fluid with GA was significantly reduced by 3.28 and 2.78 log at 24 h and 48 h, while PA only had a slight numerical decrease. VA significantly reduced ST by 4.81 and 5.20 log at 24 h and 48 h. Changes in relative abundance of major phyla were observed at 24 h for samples with GA and VA as Firmicute levels increased 8.30% and 20.90%, while Proteobacteria decreased 12.86% and 18.48%, respectively. Significant changes in major genre were observed in Acinetobacter (3.41% for GA) and Escherichia (13.53% for VA), while Bifidobacterium increased (3.44% for GA) and Lactobacillus remained unchanged. Results suggest that phenolic compounds exert different effects on certain pathogens, while supporting some commensal bacteria.

Plant-Derived Phenolic Acids Limit the Pathogenesis of Salmonella Typhimurium and Protect Intestinal Epithelial Cells during Their Interactions

“…As mentioned before, though the GI tract is a complex ecosystem with many variables that can affect the efficacy of an antimicrobial product, cell monolayers have long been used as models for studying host-pathogen interactions between bacteria and eukaryotic cells [ 38 ]. One of the factors that affects the potency of phenolic acids is pH, which has been shown in the past to either increase their antimicrobial effect or neutralize them [ 39 ]. The initial antimicrobial assay performed in DMEM with 10% FBS showed that inhibitory potential increased with concentration in the case of PA and VA, though they required high doses in order to inhibit ST to undetectable levels.…”

“…To determine changes in the antimicrobial efficacy of phenolic acid under various pH ranges within DMEM, increasing concentrations of phenolic acids within DMEM were adjusted to a pH between 3 and 10 and tested for inhibition of ST, as has been described previously with some modifications [ 39 ]. Briefly, aliquots of DMEM were either independently supplemented with increasing concentrations of GA, PA, and VA ranging from 0.0625 to 5.0 mg/mL or left untreated as the control lacking phenolic acids.…”