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. 2020 Jul 23;12(8):468.
doi: 10.3390/toxins12080468.

Nature-Identical Compounds and Organic Acids Reduce E. coli K88 Growth and Virulence Gene Expression In Vitro

Andrea Bonetti  1 , Benedetta Tugnoli  2 , Barbara Rossi  2 , Giulia Giovagnoni  1 , Andrea Piva  1   2 , Ester Grilli  1   3
Affiliations

Nature-Identical Compounds and Organic Acids Reduce E. coli K88 Growth and Virulence Gene Expression In Vitro

Andrea Bonetti et al. Toxins (Basel). .

Abstract

Post-weaning diarrhoea (PWD) is one of the long-standing challenges in pig husbandry. Due to the risks of resistance caused by antibiotics (AB) misuse, conventional treatments against Escherichia coli K88 (E. coli K88), the PWD etiological agent, urgently need to be replaced. Organic acids (OA) and nature-identical compounds (NIC) are currently finding a central role in infection management thanks to their recognized antimicrobial activity. This study investigated the susceptibility of an E. coli K88 field strain to a wide panel of AB, NIC, and OA. Secondly, we evaluated the ability of sub-lethal doses of the most active compounds to modulate the expression of E. coli K88 virulence genes. Results showed that the bacterial strain was resistant to many of the tested antibiotics, but an antimicrobial action was registered for selected NIC and OA. The quantitative PCR analysis revealed that thymol, carvacrol, eugenol, and benzoic acid were able to downregulate (p < 0.05) the expression of bacterial genes related to motility, adhesion to enterocytes, heat-labile (LT) and heat-stable (ST) toxin secretion, quorum sensing, and biofilm formation. Therefore, this study demonstrated that selected OA and NIC not only control E. coli K88 growth but also modulate the expression of many virulence genes at sub-lethal doses, thus offering new insights on their mechanism of action and suggesting a powerful tool to manage PWD.

Keywords: Escherichia coli K88; antibiotics; enterotoxins; nature identical compounds; organic acids; pigs; post-weaning diarrhoea; virulence regulation.

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Conflict of interest statement

Andrea Piva serves as a professor at the University of Bologna and is a member of the board of directors of Vetagro S.p.A. (Reggio Emilia, Italy). Ester Grilli serves as an advisor of Vetagro S.p.A.

Figures

Figure 1
Figure 1
Escherichia coli K88 growth after 24 h incubation with antibiotics (A), nature-identical compounds or organic acids (B) that reported a minimal inhibitory concentration (MIC) value against the bacterial strain during the MIC assay. Growth is expressed as a percentage relative to the control (strain only); values are presented as means of three technical replicates. In rectangles are highlighted the minimal bactericidal concentration (MBC) of each substance; for benzoic and hexanoic acid, no MBC was found up to the highest tested concentration.
Figure 2
Figure 2
Effect of different antibiotics (A), nature-identical compounds (B), and organic acids (C) on relative expression levels of E. coli K88 virulence genes related to cellular adhesion (faeG), heat-labile toxin (eltA and eltB), heat-stable toxins (estA and estB), motility (motA), quorum sensing (luxS), and biofilm formation (bssS and tnaA). Data are expressed as means (n = 3) and SEM is represented by vertical bars. For each gene, significant differences between each substance and its control are marked by asterisks (p < 0.05).
See this image and copyright information in PMC

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