Antimicrobial activity of a selection of organic acids, their salts and essential oils against swine enteropathogenic bacteria

BACKGROUND: Accurate screening of new alternative antimicrobial compounds is essential for their use to control pathogens in swine production due to the replacement of antibiotics and zinc oxide. Most in vitro studies have separately reported the antimicrobial activity of organic acids and essential oils (EOs) using diverse methods for susceptibility testing. In addition, in vitro outcomes can help in the selection of the suitable antimicrobial compound and effective combinations of these compounds in the control of pathogens of interest in pork production. Therefore, the aim of this study is to determinate the antibacterial activity of six organic acids and six EOs against Escherichia coli, Salmonella spp. and Clostridium perfringens isolates, some of them multi-resistant to antibiotics, from swine origin. The synergistic effects between the products with higher activity for each bacteria were also calculated. RESULTS: All products tested showed activity against at least one bacterial species, except for black pepper EO. The results showed that formic acid with the shortest chain length was the most effective against E. coli and Salmonella spp., while the sodium salt of coconut fatty acid distillates with long chain acids was the most effective against C. perfringens. The susceptibility of isolates tested to EOs was similar, a result that demonstrates a similar activity of these products against phylogenetically unrelated pathogens. In addition, an additive effect was shown for carvacrol-oregano EO for E. coli, formic acid-carvacrol and formic acid-thymol for Salmonella spp. and carvacrol-cinamaldehyde for C. perfringens. CONCLUSIONS: The susceptibility of isolates to EOs was similar, a result that demonstrates a similar activity of these products against phylogenetically unrelated pathogens in contrast to organic acids. In addition, an additive effect was shown for several combinations of these compounds.