Lactobacillus reuteri suppresses E. coli O157:H7 in bovine ruminal fluid: Toward a pre-slaughter strategy to improve food safety?

Yolande Bertin,Audrey Segura,Lysiane Dunière,Alexandra Durand,Chloé Habouzit,Frédérique Chaucheyras-Durand,Evelyne Forano,Federico Baruzzi,Delphine Thévenot-Sergentet,Marie Laurier,David Duchez

doi:10.1371/journal.pone.0187229

Abstract

The bovine gastrointestinal tract (GIT) is the main reservoir for enterohaemorrhagic Escherichia coli (EHEC) responsible for food-borne infections. Therefore, it is crucial to develop strategies, such as EHEC suppression by antagonistic microorganisms, to reduce EHEC survival in the GIT of cattle and to limit shedding and food contamination. Most human-derived Lactobacillus reuteri strains produce hydroxypropionaldehyde (HPA), an antimicrobial compound, during anaerobic reduction of glycerol. The capacity of L. reuteri LB1-7, a strain isolated from raw bovine milk, to produce HPA and its antimicrobial activity against an O157:H7 EHEC strain (FCH6) were evaluated in bovine rumen fluid (RF) under strict anaerobiosis. EHEC was totally suppressed when incubated in RF inoculated with L. reuteri LB1-7 and supplemented with 80 mM glycerol (RF-Glyc80). The addition of LB1-7 or glycerol alone did not modify EHEC survival in RF. Glycerol was converted to HPA (up to 14 mM) by LB1-7 during incubation in RF-Glyc80, and HPA production appeared to be responsible for EHEC suppression. The bactericidal activity of L. reuteri LB1-7, the concentration of glycerol required and the level of HPA produced depended on physiological and ecological environments. In vitro experiments also showed that EHEC inoculated in rumen fluid and exposed to L. reuteri and glycerol had a very limited growth in rectal contents. However, L. reuteri exerted an antimicrobial activity against the rumen endogenous microbiota and perturbed feedstuff degradation in the presence of glycerol. The potential administration of L. reuteri and glycerol in view of application to finishing beef cattle at the time of slaughter is discussed. Further in vivo studies will be important to confirm the efficiency of L. reuteri and glycerol supplementation against EHEC shedding in ruminants.

Highlights

Enterohaemorrhagic Escherichia coli (EHEC) are Shiga toxin-producing E. coli (STEC) responsible for severe human diseases such as haemolytic uraemic syndrome [1]
A concentration of % 104 EHEC/mL was chosen because 3–6 log10 colony-forming unit (CFU)/mL were enumerated from the rumen of steers experimentally infected with E. coli O157:H7 [29]
The production of HPA by L. reuteri was tested in filter-sterilized RF samples supplemented with 250 mM glycerol: L. reuteri suppresses EHEC in bovine rumen fluid the strains LB1-7 and F275 produced 189 and 105 mM HPA, respectively, whereas HPA was not detected in the presence of L. reuteri strains 65A, 100–23 and F70

Summary

Introduction

Enterohaemorrhagic Escherichia coli (EHEC) are Shiga toxin-producing E. coli (STEC) responsible for severe human diseases such as haemolytic uraemic syndrome [1]. The majority of infections, commonly attributed to the consumption of contaminated food is caused by EHEC with serotype O157:H7 and the gut of ruminants, mainly cattle, is considered as the principal reservoir [2]. It is important to develop nutritional or ecological strategies to reduce EHEC survival in the gastrointestinal tract (GIT) of cattle and to limit shedding and further contamination of food products. Lactobacilli, which are known to exhibit an inhibitory effect against various enteric pathogens, are widely used as probiotics or direct-fed microbials in humans and animals [3, 4]. Lactobacilli display antimicrobial activities as a result of production of metabolites such as lactic acid, bacteriocins or other non-proteinaceous molecules [4]

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