PSIX-20 Antibacterial activity of an essential oil combination against several common enteropathogens in swine production

Abstract

Essential oils (EOs) have different mechanisms, most of them targeting the bacterial wall. This fact can explain differences in the effectivity of EOs between Gram-positive and Gram-negative bacteria. Therefore, combining certain EOs can broaden their individual spectrum of efficacy due to potential synergistic effects. This trial aimed to test the in vitro antibacterial activity of an EO combination (oregano and clove oils) against a collection of relevant bacterial pathogens in swine production. The Gram-negative bacterial species chosen were Salmonella enterica ssp. enterica, Escherichia coli and Brachyspira hyodysenteriae and the Gram-positive bacterial species were Clostridium perfringens and Streptococcus suis. In addition, Lactobacillus fermentum was included to compare the susceptibility between this beneficial intestinal bacteria and the pathogens tested. The broth microdilution method at pH 6 and the subculturing from wells without bacterial growth were used to determine the minimum concentration of active principle necessary to inhibit (MIC) or kill (MBC) the 50% and 90% (MIC50/90/MBC50/90) of the population of every bacteria. The results showed that the lowest MIC50/90 were obtained for B. hyodysenteriae (37.5/75 ppm) while for S. enterica ssp. enterica (150/300 ppm), C. perfringens (150/150 ppm), E. coli (300/300 ppm) and S. suis (150/300 ppm) results were similar. Regarding the MBC50/90; B. hyodysenteriae (18.8/75 ppm) was the most susceptible pathogen, again, compared to S. enterica ssp. enterica (300/300 ppm), C. perfringens (150/150 ppm), E. coli (300/300 ppm) and S. suis (150/300 ppm). In contrast, the highest bacteriostatic/bactericidal concentrations were obtained against L. fermentum (MIC50/90 600/1,200 ppm and MBC50/90 600/2,400 ppm). These results suggest that the bacterial category (Gram-positive or Gram-negative) did not have an influence on the MIC and MBC. It can also be concluded that B. hyodysenteriae is the most susceptible enteropathogen to this EO blend. However, the in vivo effect of this combination of EOs must be further studied.