Veterinary session

The issue of antimicrobial resistance, which has now reached a global level, is a common challenge for animal and public health professionals. New alternative solutions are needed to replace antibiotics in whole or in part, such as the use of plant essential oils. This may be particularly true in farms that use large values of antibiotics in food-producing (farm) animals.

The aim of our research is to test the in vitro efficacy of a preparation containing several plant essential oil extracts (menthol, eucalyptus, thyme, camphor, ajwain, basil and turmeric) by conventional agar diffusion and minimum inhibitory concentration (MIC) value determination against facultative and obligate pathogenic bacterial strains of animal and public health importance (Escherichia coli, Staphylococcus aureus, Salmonella spp., Enterococcus spp.) and the fungal species Candida albicans. In addition, we complemented our studies with a vital staining procedure.

In our studies, conventional agar diffusion and microdilution methods gave similar results. Bacterial growth was most affected in Staphylococcus spp. isolates, with an inhibition zone size of 15.89±2.15 mm in agar diffusion and a reduction in turbidity in the microdilution method at 2-8x dilutions. For the other species, larger inhibition zone diameters (Enterococcus faecalis 6.58±0.67; Escherichia coli 5.17±1.27 mm; Pseudomonas aeruginosa 5.56±2.01 mm; Candida albicans 7.58±1.00 mm) and less turbidity in the broth (2-8x dilutions) were observed at the most concentrations. However, in none of the cases did the preparation completely inhibit bacterial growth; thus, neither bacteriostatic nor bactericidal effects can be considered. In the vitality tests, a 50% reduction in viability (EC50) was observed in only one case - a single strain of Salmonella Typhimurium, and then only at a 1:1 dilution of the preparation.

Overall, the product shows promise as an adjunctive therapy for infections caused by Staphylococcus aureus and Salmonella spp. Our results suggest that the product should be further tested in vivo in conventional animal studies, in particular to investigate its effect on reducing shedding during Salmonella Typhimurium infection, and its effects on weight gain, feed consuption and feed conversion ratio. In addition, it may be worthwhile to complement these studies with pathophysiology studies. The investigation of such new alternative antibiotic therapies is an important driver of the One Health approach in the context of animal and public health.