Abstract

Post-weaning diarrhea (PWD) is an often disease affecting piglets. It is caused mainly by enterotoxigenic Escherichia coli (ETEC) colonization in pig gut. Antibiotics has been used to prevent, combat and control PWD and its negative impact on the productivity of pig breeding sector. Nonetheless, antibiotics due to their wide antibacterial spectrum also can reach beneficial gut bacteria, such as Lactobacillus. Lately, essential oils (EOs) have emerged as a potential alternative to using antibiotics in animal breeding because of their effect on bacterial growth. Commonly, citrus EOs are by-products of food industry and the availability of these EOs in the worldwide market is huge. Thus, six commercials citrus EOs were evaluated on ETEC strains, as model of pathogenic bacteria, and on Lactobacillus species, as models of beneficial bacteria. In overall, citrus EOs exhibited a selective antibacterial activity with higher effect on pathogenic bacteria (ETECs) than beneficial bacteria (Lactobacillus). Brazilian orange terpenes (BOT) oil presented the highest selective performance and caused higher disturbances on the normal growth kinetic of ETEC than on Lactobacillus rhamnosus. The action was dose-dependent on the maximal culture density (A) and the lag phase duration (λ) of the ETEC. The highest sub-inhibitory concentration (0.925 mg/mL) extended the λ duration to ETEC eight times (14.6 h) and reduced A in 55.9%. For L. rhamnosus, the λ duration was only extended 1.6 times. Despite the fact that limonene was detected as the major compound, the selective antibacterial activity of the citrus EOs could not be exclusively attributed to limonene since the presence of minor compounds could be implicated in conferring this feature.

Highlights

  • Post-weaning diarrhea (PWD) is an often disease affecting piglets

  • The aim of this study was to evaluate the selective antibacterial activity of six commercial citrus essential oils (EOs) on enterotoxigenic Escherichia coli (ETEC) strains isolated from pig gut and on two Lactobacillus species belonging to American Type Culture Collection (ATCC), as well as to determine the chemical composition of these citrus EOs

  • inhibition zone diameter (IZD) of these oils on ETECs were >18 mm. From these four citrus EOs, Brazilian orange terpenes (BOT) stood out by exhibiting the best selective antibacterial activity (p < 0.05), since it presented the largest IZDs to all ETECs and considerable low IZDs (p < 0.05) to the two evaluated Lactobacillus species

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Summary

Introduction

Post-weaning diarrhea (PWD) is an often disease affecting piglets It is caused mainly by enterotoxigenic Escherichia coli (ETEC) colonization in pig gut. Possible Lactobacillus mechanisms to fight post-weaning infections in piglets have been described as (i) the direct inhibition of pathogen growth and its virulence by secretion of antimicrobial metabolites as bacteriocins, (ii) the modulation of microbiota composition and its activity and, (iii) the stimulation of the host immune system and improvement of intestinal barrier integrity[2] In this scenario, finding an antimicrobial feed additive with a selective antibacterial activity, high spectrum activity on pathogenic bacteria and a reduced or not effect on beneficial bacteria like Lactobacillus would be very desirable. The aim of this study was to evaluate the selective antibacterial activity of six commercial citrus EOs on ETEC strains isolated from pig gut and on two Lactobacillus species belonging to ATCC, as well as to determine the chemical composition of these citrus EOs

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