"Microbiological characterization of colloidal polyphenolic nanoparticles as alternatives to antimicrobials in livestock productions."

Antibiotics can be used in livestock production to cure diseased animals and prevent the dissemination of bacteria with zoonotic potential along the food chain. However, the use of antibiotic in the food chain might contribute to the emergence of resistant bacteria, posing a threat to animal and human health. In Europe, for example, the resistance exerted by bacteria such as Escherichia coli and Staphylococcus aureus (MRSA or methicillin-resistant Staphylococcus aureus) to major antibiotics is today recognized as a major concern. In this context, phenolic compounds, which are known to have antioxidant, anti-inflammatory, anti-cancer properties are gathering increasing interest for their antibacterial effects and are considered as natural food preservatives. Nanoparticles (NPs) can be utilized to immobilize molecules of interest, increasing their bioavailability, producing magnetically drivable vehicles, and giving targeting functions, all of which can improve the efficacy of drugs delivered. Recently, nanoparticles were successfully employed for recognizing, capturing, and inhibiting bacteria. More specifically, phenolic nanoparticles can display properties that drastically differ from the ones of molecular phenols, and they are characterized by higher stability towards oxidation. In the present thesis project, analysis was carried out to study the effects of polyphenols nanoparticles as an alternative option to chemical antimicrobials against a panel of bacteria isolated from diseased livestock animals. Two types of soluble phenolic nanoparticles (NPs), industrially obtained from chestnut manufacturing, were tested using a panel of 6 bacteria isolated from cattle and poultry livestock’s (i.e., Pasteurella multocida, Staphylococcus aureus, Streptococcus suis, Mannhemia haemolitica, Escherichia coli, Salmonella typhimurium). The methodology used to assess the properties of the phenolic nanoparticles was the Minimum inhibitory Concentration (MIC), which is defined as the lowest concentration of a drug/compound capable of inhibiting the growth of a microorganism in vitro. The initial concentration of phenol-based NPs was 100 mg/L. In 96-well micro-titter plates, two-fold serial dilutions of the phenolic NPs were carried out (NP final concentration: 15, 7.5, 3.75, 1.875, 0.9375 and 0.46875mg/L) and incubated with of 5 log cfu/ml of the bacteria inoculum. Positive and negative control were also performed. For each bacterium of the panel, the growth curves, as a function of NP concentration, were assessed via Uv-vis Spectrophotometry by measuring the absorbance at 600.0 nm. For each plate, three different biological replicates were performed, and all experiments were performed in duplicate and MIC average values with standard deviation were calculated. The results showed that these nanoparticles have different effects depending on the examined bacteria, inhibiting the microorganism growth at significantly low concentrations (up to 15 mg/l). Notably, one of the NPs was effective against antibiotic resistant pathogens such as Staphylococcus aureus (gram positive bacteria) and Mannhemia haemolitica (gram negative bacteria).