Probiotics strains are more resistant than Enterococcus cecorum to the antimicrobial action of botanicals

Plain text summary The antimicrobial effect of seven botanicals was tested against four probiotic strains (L. acidophilus, L. paracasei, L. rhamnosus and E. faecium) in comparison with E. cecorum, a chicken intestinal pathogen. Minimal inhibitory concentrations and minimal bactericidal concentrations were higher for the probiotic strains compared to E. cecorum. Thus, selected botanicals can be used with probiotics to control pathogens, without interfering with beneficial bacteria growth. Main text Introduction and Aims Botanicals are well-known for their antimicrobial action to inhibit intestinal pathogens in livestock. However, it is not clear whether they could affect also the beneficial microflora or supplemented probiotics. Aims and Objectives This study aimed to investigate in vitro the inhibitory and bactericidal effect of various botanicals against four probiotic strains in comparison with a chicken intestinal pathogen. Material and Methods Lactobacillus acidophilus (LA), Enterococcus faecium (EF), Lactobacillus rhamnosus (LR), Lactobacillus paracasei (LP) and Enterococcus cecorum (EC) were used for this study. Vanillin, thymol, carvacrol, eugenol, α-pinene, limonene and cinnamaldehyde were tested using a microdilution method from 30 to 0.24 mM (2-fold dilutions) for 24 h. Minimal inhibitory concentration (MIC) was considered the lowest dose giving null absorbance. Samples with null absorbance were seeded on agar to assess minimal bactericidal concentrations (MBC) after 24 h. Results MIC values against the four probiotics were found for vanillin, α-pinene, limonene (30 mM), eugenol (15 mM), thymol, carvacrol (7.5 mM) and cinnamaldehyde (3.75 mM). Against EC, MIC values were found for α-pinene, limonene (30 mM), vanillin, eugenol, cynnamaldehyde (3.75 mM), thymol and carvacrol (1.87 mM). Vanillin, thymol, carvacrol and eugenol killed all the bacteria, with MBC values at least 2 times higher for probiotics than for EC. Cinnamaldehyde was bactericidal only on LA, EF and EC. Conclusion(s) Probiotics are generally more resistant to botanicals compared to E. cecorum, suggesting that botanicals at the right concentrations could be used to positively modulate chicken microflora, controlling pathogens without interfering with beneficial bacteria.