Expression of ompR gene in the acid adaptation and thermal resistance of Salmonella Enteritidis SE86.

Ana Carolina Ritter,Eduardo Cesar Tondo,Sergio Uzzau,Donatella Bacciu,Salvatore Rubino,Lucelia Santi

doi:10.3855/jidc.3584

Abstract

The objective of this study was to evaluate the involvement of the ompR gene in the acid adaptation and thermal resistance of S. Enteritidis SE86, responsible agent of more than 95 % of investigated food-borne diseases, throughout the last decade in Southern Brazil. In this study, we constructed a mutant strain of S. Enteritidis SE86 (ΔompR) that was attenuated by a knockout technique. The OmpR protein expression was determined in a tagged (3XFLAG) strain of S. Enteritidis SE86. The mutant strains were cultivated separately in nutrient broth and nutrient broth supplemented with 1% glucose (NBG) to induce acid adapted cells. The organisms were exposed to different temperature such as 37 ºC, 52 ºC, and 60ºC. The survival of the SE86 wild type (WT) and attenuated strain was determined by bacterial count, and the tagged protein (ompR::3XFLAG cat::FLAG) was detected by SDS-PAGE and immunoblotting with anti-FLAG antibodies. Results showed that when exposed at 52ºC, the acid-adapted SE86 WT cells were completely inactivated after 300 minutes; however, non-adapted cells (WT and ΔompR) and acid-adapted ΔompR demonstrated higher thermal sensitivity, since they were completely inactivated in 240 minutes. At 60ºC, the acid-adapted SE86 ΔompR also demonstrated higher sensitivity that SE86 WT, being totally inactivated after 15 minutes, while the WT cells were inactivated in 20 minutes. The acid adapted cells showed increased expression of OmpR when exposed to 52 ºC and 60ºC, this confirmed the requirement of acid adaptation for S. Enteritidis SE86 to resist elevated temperatures.

Highlights

The objective of this study was to evaluate the involvement of the ompR gene in the acid adaptation and thermal resistance of S
Salmonella grown in nutrient broth supplemented with 1% glucose (NBG) was considered acidadapted, while Salmonella cultivated in nutrient broth (NB) was considered non-adapted
In this study we confirmed the involvement of the OmpR protein in the acid adaption of Salmonella Enteritidis SE86, a fact that has already been reported by other studies with different Salmonella serovars

Summary

Introduction

The objective of this study was to evaluate the involvement of the ompR gene in the acid adaptation and thermal resistance of S. Salmonella enterica encompasses more than 2,600 serotypes [1]; of which Salmonella serovars Enteritidis Typhimurium are most commonly involved in salmonellosis [2] Both outside of the host and during infection, Salmonella encounter numerous environmental stressors, which can trigger physiologic responses which may be potentially lethal to Salmonella, and the survival of these microorganisms depends on their ability to adapt or respond to these stressors [3]. Stress adaptation of Salmonella cells can be induced in the exponential and stationary phases During both phases, an increased resistance to acid and thermal stress can occur [4]. In order to promote acid adaptation, Salmonella serotypes express two low-pHinducible systems known as “Acid Tolerance Response” (ATR), which are classified based on the growth phase at which each becomes induced. The regulatory gene rpoS, encoding an alternative sigma factor, is required for log-phase acid tolerance and for control of the production of clusters of ASPs [6, 3]

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Methods

Conclusion