Abstract
Salmonella enterica serovar Typhimurium (ST) remains a major infectious agent in the USA, with an increasing antibiotic resistance pattern, which requires the development of novel antimicrobials capable of controlling ST. Polyphenolic compounds found in plant extracts are strong candidates as alternative antimicrobials, particularly phenolic acids such as gallic acid (GA), protocatechuic acid (PA) and vanillic acid (VA). This study evaluates the effectiveness of these compounds in inhibiting ST growth while determining changes to the outer membrane through fluorescent dye uptake and scanning electron microscopy (SEM), in addition to measuring alterations to virulence genes with qRT-PCR. Results showed antimicrobial potential for all compounds, significantly inhibiting the detectable growth of ST. Fluorescent spectrophotometry and microscopy detected an increase in relative fluorescent intensity (RFI) and red-colored bacteria over time, suggesting membrane permeabilization. SEM revealed severe morphological defects at the polar ends of bacteria treated with GA and PA, while VA-treated bacteria were found to be mid-division. Relative gene expression showed significant downregulation in master regulator hilA and invH after GA and PA treatments, while fliC was upregulated in VA. Results suggest that GA, PA and VA have antimicrobial potential that warrants further research into their mechanism of action and the interactions that lead to ST death.
Highlights
Death because of enteric infections was found to be the third highest transmittable cause of death in the world, with diarrheal disease being the main source and infection by the bacterial pathogenSalmonella spp. responsible for at least 18.7% of those deaths [1]
Invasive Salmonella enterica serovar Typhimurium (ST) infections are mediated through the activation of the genes found in the Salmonella Pathogenicity Island 1 (SPI-1), which code for an assembly of proteins known as the Type III Secretion System (T3SS) that aid in the attachment and subsequent invasion of host cells [9]
This study evaluates the antimicrobial potential of three phenolic acids known to be in berry pomace extract (BPE), with the aim of comparing their individual effectiveness against ST
Summary
Death because of enteric infections was found to be the third highest transmittable cause of death in the world, with diarrheal disease being the main source and infection by the bacterial pathogenSalmonella spp. responsible for at least 18.7% of those deaths [1]. Even though incidence is most pervasive in developing parts of the world, enteric disease caused by foodborne pathogens still accounts for substantial cases of illness, hospitalization, death and economic loss in the USA [2]. Of the major 31 pathogens associated to foodborne illness in the USA, Salmonella enterica is the leading bacterial etiological agent as it is estimated to be responsible for over 1 million cases of illness, 15,000 hospitalizations, 300 deaths, and an estimated loss of 3.5 billion dollars yearly, associated with the loss of productivity that accounts for cost of care, treatment, recovery and hours of work lost [3,4]. The continuous and increasing discovery of antibiotic-resistant ST isolates from human samples [14], as well as in farm animals meant for consumption, poses a growing public health threat, greatly exacerbated by the need for novel antimicrobial compounds that do not add to the development of resistance
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