Thymol and Carvacrol Downregulate the Expression of Salmonella typhimurium Virulence Genes during an In Vitro Infection on Caco-2 Cells

Giulia Giovagnoni,Ester Grilli,Benedetta Tugnoli,Barbara Rossi,Federico Ghiselli,Andrea Bonetti,Andrea Piva

doi:10.3390/microorganisms8060862

Abstract

Salmonella typhimurium is one of the major bacteria responsible for gastroenteritis in humans caused by foodborne pathogens. As pork is one of the main routes of transmission, bioactive compounds used as feed additives may be an important strategy to control Salmonella typhimurium. The aim of this study was to assess the antimicrobial activity of several organic acids and nature identical compounds against Salmonella typhimurium ATCC®® 6994™. Moreover, the effect of sub-lethal concentrations of thymol and carvacrol in counteracting a Salmonella typhimurium in vitro infection on Caco-2 cells was evaluated, focusing on the maintenance of the epithelial barrier and the alteration of Salmonella virulence genes. The results showed a protective effect of the compounds on the integrity of the intestinal monolayer, improving transepithelial electrical resistance and bacterial translocation compared to the non-treated cells. A real-time PCR study highlighted a significant downregulation of the main virulence genes of Salmonella (hilA, prgH, invA, sipA, sipC, sipD, sopB, sopE2). These findings indicate that thymol and carvacrol could be good candidates for the control of Salmonella typhimurium in pigs.

Highlights

Salmonella typhimurium is a Gram-negative foodborne pathogen, reported as the second and third most common cause of human gastrointestinal infections in Europe and the United States, respectively [1,2]
The results showed a protective effect of the compounds on the integrity of the intestinal monolayer, improving transepithelial electrical resistance and bacterial translocation compared to the non-treated cells
These findings indicate that thymol and carvacrol could be good candidates for the control of Salmonella typhimurium in pigs

Summary

Introduction

Salmonella typhimurium is a Gram-negative foodborne pathogen, reported as the second and third most common cause of human gastrointestinal infections in Europe and the United States, respectively [1,2]. Structural proteins are responsible for the assembly of the T3SS apparatus, formed by two rings crossing the inner and outer bacterial membrane, linked to a needle-like system that pierces the host cellular membrane [10,11]. The latter structure is crucial for the transport of the effector proteins, delivered by translocators from the bacterial cell into the host: here, effectors manage fundamental changes enabling key steps for Salmonella pathogenesis [12]. It has been demonstrated that several effector proteins encoded by SPI-1, such as SipA, SopB, SopE, and SopE2, are responsible for alteration of these parameters [16]

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