Highly Specific Polyphenolic Colloids as Alternatives to Antimicrobials in Livestock Production

Abstract

The dispersion of antibiotics in livestock farming represents a health concern worldwide, contributing to the spread of antimicrobial-resistant bacteria through animals, the environment, and humans. Phenolic compounds could be alternatives to antibiotics, once drawbacks such as their low water solubility, bioavailability, and reduced stability are overcome. Although nano- or micro-sized formulations could counter these shortcomings, they do not represent cost-effective options. In this study, three phenolic compounds, obtained from wood-processing manufacturers, were characterized, revealing suitable features such as their antioxidant activity, size, and chemical and colloidal stability for in-field applications. The minimum inhibitory concentration (MIC) of these colloidal suspensions was measured against six bacterial strains isolated from livestock. These particles showed different inhibition behaviors: Colloidal chestnut was effective against one of the most threatening antibiotic-resistant pathogens, i.e., S. aureus, but ineffective toward E. coli. Instead, colloidal pine showed a weak effect on S. aureus but specificity toward E. coli. The present proof-of-concept points at colloidal polyphenols as valuable alternatives for antimicrobial substitutes in the livestock context.

Keywords: AMR; antimicrobials; nanoparticles; wood industry by-products.

Figure 1

Hydrodynamic and morphological characterization of the colloidal phenols. DLS hydrodynamic radii of (A) CCA, (B) CCB, and (C) CP. TEM micrographs of (D) CCA, (E) CCB, and (F) CP.

Figure 2

Chemical characterization of the phenol dried powders. FTIR profile of (A) CCA, (B) CCB, (C) CP, and (D) commercial tannic acid, used as a control. Comparison of the antioxidant powers through (E) FRAP and (F) Folin–Ciocalteâu assays.

Figure 3

Study of the disaggregation and oxidation behaviors of CCA, CCB, and CP. The effect of increasing pH values documented by UV-vis spectroscopy for (A) CCA, (B) CCB, and (C) CP. Comparison of the evolution of the aromatic phenol ring’s UV-vis peak at 280 nm as a function of time at (D) pH 7, (E) pH 8, and (F) pH 12. (G) Comparison of color variation as a function of the pH. (H) Comparison of antioxidant powder as a function of the pH.

Figure 4

MIC determination for CCA (blue), CCB (red), and CP (green) against S. aureus (A), M. haemolytica (B), P. multocida (C), S. suis (D), S. Typhimurium (E), and E. coli (F). Each point in a logarithmic horizontal axis of colloid concentrations represents the mean O.D. of six independent replicates, with the vertical whiskers indicating the standard deviation (SD). The horizontal dashed lines represent the MIC threshold set at a 0.05 increase in O.D. Bacterial strains inoculated without any compound were used as positive controls and are shown in purple.