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.

In this study, the effect of sustainable probiotics on Campylobacter jejuni colonization and gut microbiome composition was evaluated using chicken as a model organism. Chickens were given Lactobacillus casei over-expressing myosin-cross-reactive antigen (LC+mcra). LC+mcra can generate bioactive compounds in larger quantity including conjugated linoleic acid. A total of 120 chickens were used in duplicate trials to investigate the effectiveness of LC+mcra in decreasing C. jejuni colonization by means of kanamycin resistant strain compared to the control group. We observed that LC+mcra can efficiently colonize various parts of the chicken gut and competitively reduce colonization of natural and challenged C. jejuni and natural Salmonella enterica. LC+mcra was found to reduce C. jejuni colonization in cecum, ileum and jejunum, by more than one log CFU/g when compared to the no-probiotic control group. Furthermore, 16S rRNA compositional analysis revealed lower abundance of Proteobacteria, higher abundance of Firmicutes, along with enriched bacterial genus diversity in gut of LC+mcra fed chicken. Decreased contamination of drinking water by C. jejuni and S. enterica was also observed, suggesting a potential function of reducing horizontal transfer of enteric bacteria in poultry. Outcomes of this study reveal high potential of LC+mcra as sustainable approach to decrease colonization of C. jejuni and S. enterica in poultry gut along with other beneficial attributes.

Enhancing extracellular metabolic byproducts of probiotics is one of the promising strategies to improve overall host health as well as to control enteric infections caused by various foodborne pathogens. However, the underlying mechanism of action of those metabolites and their effective concentrations are yet to be established. In this study, we determined the antibacterial potential of the metabolites in the cell-free culture supernatant (CFCS) collected from wild-type Lactobacillus casei (LCwt) and genetically modified LC to overexpress linoleate isomerase (LCCLA). We also evaluated the mechanism of action of CFCSs collected from the culture of LCwt in the presence or absence of 0.5% peanut flour (CFCSwt and CFCSwt+PF, respectively) and LCCLA alone (CFCSCLA) against enterohemorrhagic Escherichia coli (EHEC). The metabolites present in CFCSwt+PF and CFCSCLA eliminated EHEC within 24 and 48 h, respectively. Whereas CFCSwt failed to eliminate EHEC but reduced their growth by 6.7 logs (p < 0.05) as compared to the control. Significant downregulation of the expression of cell division gene, ftsZ, supported the observed degree of bactericidal and bacteriostatic properties of the collected CFCSs. Upregulation of EHEC genes related to maintaining cell membrane integrity, DNA damage repair, and molecular chaperons indicated an intensive stress condition imposed by the total metabolites present in CFCSs on EHEC growth and cellular structures. A range of deviated morphological features provoked by the metabolites indicated a membrane-targeted action, in general, to compromise the membrane permeability of EHEC. The information obtained from this study may contribute to a more efficient prevention of EHEC related infections.

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Organic farming, including integrated crop-livestock farms (ICLF) and backyard farming (BF), are gaining popularity in the US, and products from these farms are commonly sold in farmers markets, local stores, or roadside stalls. Due to avoiding use of antibiotics and chemicals, as well as the non-professional harvesting and packaging methods, and the use of composted animal waste, there is an increased risk of cross-contamination with zoonotic pathogens. This study sets out to evaluate the efficiency of new post-harvest disinfection processes using natural berry pomace extracts (BPE) as a means to reduce the bacterial load found in two common leafy-greens, spinach and celery. Both spinach and celery were inoculated with a fixed bacterial load of Salmonella Typhimurium (ST) and later soaked in BPE supplemented water (wBPE) for increasing periods of time, and at two different temperatures (24°C and 4°C). The remaining live bacteria were quantified in Log of CFU/leaf and compared to that of vegetables soaked in only water. The relative expression of virulence genes ( hilA1/C1/D1, invA1/C1/E1 / F1 ) of wBPE treated ST was determined. Results show that in the case of spinach, there was a significant ( p <0.05) reduction of ST from a range of 0.2 to1.2 log CFU/mL and 0.5 to 5 log CFU/mL at 24°C and 4°C, respectively. For celery there was also a significant ( p <0.05) reduction of ST at either 24°C or 4°C. The changes in relative expression of virulence genes of ST isolated from spinach and celery varied depending on the treatment conditions but showed a significant downregulation of inv genes when treated at 24°C for 1440 minutes ( p <0.05). After 7 uses of wBPE, concentration of total polyphenolic compounds remains at the effective concentration. This research suggests that soaking these vegetables with BPE containing water at lower temperatures can still reduce load of ST enough to minimize risk of infection and alter the virulence properties.