PS12-3. In vitro Toxicity of Onion Peel Powder, Apple Peel Powder, and Guinea Hen Weed Powder on Salmonella Spp.

Abstract

The incidence and continued occurrence of resistant foodborne pathogens in food animals and the industry have raised growing awareness among consumers, emphasizing the need for alternative strategies, such as phytogenic plant-based interventions, as a safer and sustainable substitute for traditional antibiotics. Therefore, an in vitro study was conducted to evaluate the comparative activities of Onion Peel Powder OPP, Apple Peel Powder APP and Guinea Hen Weed Powder (GHW) against Salmonella Typhimurium ST. Salmonella Typhimurium were cultured as follows: without additives (Control), with OPP, APP and GHW at different concentration (0.049, 0.098, 0.195, 0.39, 0.78,1.56, 3.125, 6.25, 12.5 mg/ml). Minimum inhibitory concentration (MIC) of the extracts was determined by p-iodonitrotetrazolium chloride (INT) colorimetric assay. ST cultures were incubated without additives (control) or with OPP, APP, and GHW at their respective sub-MIC concentrations. ST culture samples (supernatants) were analyzed for lipopolysaccharide (LPS) concentration, while total RNA extracted from bacterial pellets to assess the expression of molecular indicators of virulence-associated genes (spvC, invA, sopE, and hilA) and antimicrobial resistant genes (blaTEM, blaCTX, tetA, tetB, sul1, sul2, qnrA, qnrB) in ST. Results showed that the MIC for OPP and APP was 0.1953 mg/mL, while that of GHW was 0.3906 mg/mL. Compared with the control (206.5 pg/mL), phytogenic extracts significantly reduced (P < 0.0001) Salmonella LPS concentrations to 50.77, 49.29, and 34.52 pg/mL, respectively. All three phytogenic extracts downregulated (p < 0.05) spvC, indicating their potential in limiting post-invasion survival of ST. All three phytogenic extracts reduced (p < 0.05) the level of expression of invA virulence gene, a prerequisite for epithelial cell invasion. This finding suggests that extracts can impair the early stages of host colonization by directly targeting invasion machinery. Similarly, all extracts reduced (p < 0.05) sopE expression, a key effector responsible for manipulating host cell signaling and promoting inflammation, demonstrating a capacity of extracts to depress host-pathogen interactions that drive disease severity. The expression of hilA was most downregulated by OPP, followed by APP and GHW. Suppression of hilA suggests upstream interference with the regulatory cascade governing SE invasiveness, potentially resulting in broad attenuation of virulence gene networks. In addition, all extracts suppressed ARGs associated with β-lactam resistance (blaTEM, blaCTX), tetracycline resistance (tetA, tetB), quinolone resistance (qnrA, qnrB), & sulfonamide resistance (sul1, sul2) (p < 0.05). Noteworthy, the lowest expression of qnrB was observed in GHW. The broad suppression of ARGs representing multiple resistance mechanisms suggests interference with key regulatory pathways involved in antimicrobial resistance. Overall, these results demonstrate that phytogenic extracts exert dual antimicrobial effects against ST. By concurrently reducing bacterial load, suppressing invasion, survival, and interference with ARGs expressions, these phytogenics offer a biologically effective strategy for improving poultry health, safeguarding food safety, and reducing dependence on traditional in-feed antibiotics.