Unraveling the selective antibacterial activity and chemical composition of citrus essential oils

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.

Enzymatic hydrolysis of orange bagasse and effect of filtration on lactic acid fermentation

“…The attachment of inhibitory components to insoluble residues during the hydrolysis could provide their separation from the medium by a simple filtration technique as reported in a previous study of Grohmann et al They showed that filtration decreased limonene concentration in the filtrate below the inhibition level (0.05% and 0.1%) and allowed them to produce ethanol from orange peel by the yeast S. cerevisiae [14]. The interpretation of the current result could also be strengthened by comparing the inhibition levels of various [15,16]. Furthermore, this study showed that the heat treatment at higher temperatures could help for the elimination of some inhibitory compounds found in orange waste even though the ineffectiveness of vacuum evaporation, a process performed at a lower temperature, on the removal of limonene due to its low volatility pointed out in [14].…”

In vitromechanism of antibacterial action of a citrus essential oil on an enterotoxigenicEscherichia coliandLactobacillus rhamnosus

“…The BOT oil evaluated in this study, previously has been proved for presenting an anti-ETEC activity and reduced activity on Lactobacillus sp. (Ambrosio et al 2019).…”

“…This was carried out following the approach described by Ambrosio et al (2018). The SE was carried out considering the MIC of BOT for E. coli U21 (1Á85 mg ml À1 ) that was previously determined by Ambrosio et al (2019). Each BOT stock solution was prepared in Mueller Hinton (MH) broth or MRS broth using Tween 80 as an emulsifier in a ratio of 8 : 1 (EO : Tween 80, v/v), since at this ratio no antimicrobial activity of Tween 80 was observed.…”

“…The chemical composition profile of BOT was determined by gas chromatography coupled with mass spectrometry (GC/MS) using non-polar and polar columns as described by Ambrosio et al (2019). The analysis on the nonpolar column was carried out in an Agilent Technology gas chromatograph 6890 Plus Series (Santa Clara, CA) coupled to a selective Mass Spectrometry Detector 5973 and an Auto Sampler 7893.…”

“…Nonetheless, it has been reported that citrus EOs present a selective antibacterial activity, causing lower effects on the growth kinetics of Lactobacillus sp. than ETECs (Ambrosio et al 2019). Thus, it is important to unveil the mechanism of antibacterial action of citrus EOs on Lactobacillus as well as on ETECs in view of the limited information regarding this.…”