The In Vitro Antibacterial Activity of Phytogenic and Acid-Based Eubiotics against Major Foodborne Zoonotic Poultry Pathogens

Abstract

The aim of the study was to investigate in vitro the antibacterial activity of 8 commercial drinking water additives against major zoonotic poultry pathogens (Campylobacter spp., Escherichia coli, Salmonella Typhimurium, Staphylococcus aureus and Listeria spp.). We tested two essential oil-based phytogenics (Phyto CSC Liquide B, AEN 350 B Liquid), two acid-based eubiotics (Salgard^® liquid, Intesti-Flora), and four blends of essential oils and organic acids (ProPhorce^TM SA Exclusive, Herbal acid, Rigosol-N and Eubisan 3000). The antibacterial activity was determined by estimating the minimum inhibitory concentration (MIC) using a microdilution method. The MICs of the products against Campylobacter spp. ranged from 0.071% to 0.568% v/v, in which Herbal acid, a blend rich in lactic and phosphoric acids, also containing thyme and oregano oils, exhibited the highest efficacy (MIC: 0.071% v/v) against all the tested strains. The MICs of the tested products against Escherichia coli ranged between 0.071% and 1.894% v/v. Specifically, the MIC of Rigosol-N, a blend of high concentrations of lactic and acetic acid, was 0.142% v/v for both tested strains, whereas the MICs of Intesti-Flora, a mixture rich in lactic and propionic acid, ranged from 0.284% to 0.568% v/v. The MICs of the products against Salmonella Typhimurium were between 0.095% and 1.894% v/v. Specifically, the MIC of Eubisan 3000, a blend rich in oregano oil, was 0.284% v/v. The MICs against Staphylococcus aureus were between 0.142% and 9.090% v/v. The MICs of Phyto CSC Liquide B, which is rich in trans-cinnamaldehyde, were between 3.030% and 9.090% v/v, showing the highest MIC values of all tested products. Finally, the MIC values of the tested commercial products against Listeria spp. were 0.095% to 3.030% v/v. The MICs of ProPhorce^TM SA Exclusive, a highly concentrated blend of formic acid and its salts, were 0.095-0.142% v/v against Listeria spp., while the MICs of AEN 350 B Liquid were between 0.284% and 1.894% exhibiting high Listeria spp. strain variability. In conclusion, all the selected commercial products exhibited more or less antibacterial activity against pathogenic bacteria and, thus, can be promising alternatives to antibiotics for the control of zoonotic poultry pathogens and the restriction of antimicrobial-resistant bacteria.

Keywords: acid-based eubiotics; antimicrobial activity; minimum inhibitory concentration (MIC); phytogenic additives; poultry; zoonotic bacteria.

Figure 1

Schematic representation of the microdilution MIC method used to evaluate the antibacterial activity of the commercial drinking water additives against major zoonotic poultry bacteria. The numbers 1–12 referred to the gradient concentrations of the tested products while letters A–C referred to the treatment groups, letter E to positive control, letters G and H to the negative controls, and letters D and F were blank.

Figure 2

Graphs of recorded MIC values (columns; mean %v/v ± SD) of the tested commercial products on the tested (A) Campylobacter, (B) E.coli and (C) S. Typhimunium strains.

Figure 3

Graphs of recorded MIC values (columns; mean %v/v ± SD) of the tested commercial products on the tested (A) S. aureus and (B) Listeria spp. strains.