Abstract
Alternative antimicrobials require a deep understanding of their action mechanisms by in vitro assays which support science-based field use. This study focuses on the characterization of bactericidal mechanisms of potential antimicrobial compounds, two organic acids and three single essential oil (EO) compounds against swine enteropathogenic bacteria Escherichia coli, Salmonella enterica subsp. enterica serovar Typhimurium, and Clostridium perfringens. Target concentrations of the compounds were evaluated using the inhibitory potential of the vapor phase and bacterial viability after short-term exposure, while cell targets were disclosed using flow cytometry (FC), Fourier-transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). All tested compounds exhibited vapor phase activity against the three bacterial species, except sodium salt of coconut fatty acid distillates against C. perfringens. Survival test results evidenced that effects on bacterial viability were concentration dependent and higher in single EO compounds than in organic acids. In detail, thymol and its isomer carvacrol were the most effective compounds. Further characterization of thymol and cinnamaldehyde activity revealed that thymol main target was the cell membrane, since it caused striking damages in the membrane permeability, integrity and composition evidenced by FC and FTIR in the three enteric pathogens. In contrast, cinnamaldehyde was more effective against enterobacteria than against C. perfringens and only caused slightly damages at the highest concentration tested. Its target at the molecular level differed between enterobacteria and C. perfringens isolates. The SEM micrographs allowed us to confirm the results previously obtained for both EO compounds by other techniques. Altogether, the study showed the straight effect of these antimicrobials, which could constitute relevant information to optimize their feed inclusion rates in field studies or field use.
Highlights
The emergence of antimicrobial resistance (AMR) is a major worldwide public health concern, which reduces the efficacy of antibiotic treatments in human and animal infections [1]
This study aims at extending the knowledge acquired in the in vitro evaluation of the antimicrobial activity of two organic acids, formic acid and sodium salt of coconut fatty acid distillates, three single essential oil (EO) compounds, thymol, cinnamaldehyde, and carvacrol against a selection of animal enteric pathogenic bacteria [11]
The information gathered was used to evaluate, at target concentrations and through different acknowledged techniques [18], the mechanisms by which these compounds exert their activity against E. coli, S
Summary
The emergence of antimicrobial resistance (AMR) is a major worldwide public health concern, which reduces the efficacy of antibiotic treatments in human and animal infections [1]. These studies stress that the mode of action and target structures or processes in pathogenic bacteria are not completely understood [3, 13,14,15] In this context, information regarding their effect on bacterial viability after short-term exposure and the inhibitory potential of vapor phase of these compounds has been poorly revised [13, 16]. Information regarding their effect on bacterial viability after short-term exposure and the inhibitory potential of vapor phase of these compounds has been poorly revised [13, 16] It draws attention the usefulness of precise techniques such as flow cytometry (FC) or Fourier-transform infrared (FTIR) spectroscopy to add information about the mode of action of single alternative compounds. Both techniques are considered as powerful non-destructive tools to obtain physiological, compositional, and structural information of bacteria after the exposure of different experimental conditions or compounds [17, 18]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
