Tolerance response of multidrug-resistant Salmonella enterica strains to habituation to Origanum vulgare L. essential oil.

Daniel F. M. Monte,Adassa G. Tavares,FÃ¡bio C. Sampaio,Allan R. Albuquerque,Marciane Magnani,Tereza C. R. M. Oliveira,Evandro L. Souza,Octavio L. Franco

doi:10.3389/fmicb.2014.00721

Abstract

Multidrug-resistant Salmonella enterica isolates from human outbreaks or from poultry origin were investigated for their ability to develop direct-tolerance or cross-tolerance to sodium chloride, potassium chloride, lactic acid, acetic acid, and ciprofloxacin after habituation in subinhibitory amounts ( of the minimum inhibitory concentration – (MIC) and of the minimum inhibitory concentration – MIC) of Origanum vulgare L. essential oil (OVEO) at different time intervals. The habituation of S. enterica to OVEO did not induce direct-tolerance or cross-tolerance in the tested strains, as assessed by the modulation of MIC values. However, cells habituated to OVEO maintained or increased susceptibility to the tested antimicrobials agents, with up to fourfold double dilution decrease from previously determined MIC values. This study reports for the first time the non-inductive effect of OVEO on the acquisition of direct-tolerance or cross-tolerance in multidrug-resistant S. enterica strains to antimicrobial agents that are largely used in food preservation, as well as to CIP, the therapeutic drug of salmonellosis.

Highlights

Salmonella enterica is recognized as the most frequent cause of foodborne disease in the world (Hendriksen et al, 2011; GomesNeto et al, 2014)
This study reports for the first time the non-inductive effect of Origanum vulgare L. essential oil (OVEO) on the acquisition of direct-tolerance or cross-tolerance in multidrug-resistant S. enterica strains to antimicrobial agents that are largely used in food preservation, as well as to CIP, the therapeutic drug of salmonellosis
Knowledge about the magnitude of tolerance induction in foodborne pathogens, in S. enterica, which possesses a large diversity of resistance mechanisms (Spector and Kenyon, 2012), must be a requisite for the development of anti-bacterial compounds, such as OVEO, that are considered for application in food preservation systems. Considering these aspects, the aim of this study was to assess the effects of the exposure of multidrug-resistant epidemic S. enterica strains to subinhibitory concentration of OVEO for different time intervals on the development of bacterial tolerance to salts and organic acids used by the food industry, as well to CIP, a therapeutic drug of human salmonellosis

Summary

Introduction

Salmonella enterica is recognized as the most frequent cause of foodborne disease in the world (Hendriksen et al, 2011; GomesNeto et al, 2014). A number of studies have shown that previous exposure of S. enterica to a single stressful condition could result in homologous or heterologous tolerance and increasing subsequent resistance to the same or different environment stresses (Álvarez-Ordóñez et al, 2010; Dubois-Brissonnet et al, 2011; Shah et al, 2013). It has been reported that the exposure of S. enterica to subinhibitory conditions imposed by these classical antimicrobial compounds can undergo genetic and physiologic changes. These changes allow the cells to become more resistant in subsequent exposures to the antimicrobial compounds, due to the development of a tolerance response (Álvarez-Ordóñez et al, 2012; Spector and Kenyon, 2012; Yang et al, 2014)

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