Inhibition of Virulence Gene Expression in Dublin, F5 and Associated With Neonatal Calf Diarrhea by Factors Produced by Lactic Acid Bacteria During Fermentation of Cow Milk
Overview
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Diarrhea is a major health problem in neonatal and young calves worldwide. It can be caused by a variety of infectious agents, including the bacteria serovar Dublin (. Dublin), enterotoxigenic (ETEC), and . Preventive alternatives to antibiotic treatment should be identified. As a first step toward this, the aim of the current study was to examine whether cell-free supernatants from cow milk fermented by lactic acid bacteria affects virulence-gene expression in strains of . Dublin, ETEC F5 and . pH-neutralized, cell-free, spent medium of milk (nCFSM) fermented by 61 different lactic acid bacteria (LAB) and non-LAB starter cultures belonging to 17 genera was assayed for their effect on expression of important virulence factors (. Dublin ; ETEC F5 ; ), when the bacteria were grown in the nCFSM. Screening was done using either a promoter-reporter expression system or RT-qPCR. nCFSM from BL-15955 and LR-33016 downregulated the expression of and genes in the four tested ETEC F5 strains without affecting their growth, while mainly BL-15955 downregulated expression of in the four tested strains of . nCFSM from the mixed cultures; NU-TRISH BY-Mild ( subsp. and BL-15954) and COMBO4 ( subsp. and ), as well as CNRZ32 downregulated the tested virulence genes in the three tested strains of . Dublin. To enable possible downregulation of the expression of virulence genes in all three target bacteria simultaneously, nCFSM was prepared from NU-TRISH By-Mild in combination with BL-15955 (i.e. a four-strain combination). The nCFSM from this combination downregulated the virulence genes expression in all the three species. In the future, NU-TRISH By-Mild and BL-15955 in combination could potentially be used for prevention of neonatal calf diarrhea caused by . Dublin, F5, and , reducing the need for antimicrobial treatment, however, field studies are needed to prove that.
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