Yogurt containing bioactive molecules produced by Lactobacillus acidophilus la-5 exerts a protective effect against enterohemorrhagic Escherichia coli in mice

An active fraction extracted from Lactobacillus acidophilus La5 cell-free spent medium (LAla-5AF) was incorporated in a dairy matrix and tested to assess its antivirulent effect against enterohemorrhagic Escherichia coli (EHEC). Mice inexperimentalgroups were fedfor 4 days with yogurt supplemented with LAla-5AF. On the fifth day, mice were challengedwith a single dose(107 CFU per mouse) of E. coli O157:H7. The clinical manifestations of the infection were significantly less severe in mice fed the yogurt supplemented with LAla-5AF. EHEC attachment and colonization was attenuated by LAla-5AF. Tumor necrosis factor alpha production was down-regulated, which might indicate a protective effect in the kidney during EHEC infection. To investigate the mechanisms associated with the in vivo effects observed, LAla-5AF was tested by reverse transcription real-time PCR to confirm its effects on the expression of several virulence genes of EHEC O157. The results showed that these fractions were able to down-regulate several virulence genes of EHEC,including stxB2, qseA, luxS, tir, ler, eaeA, and hlyB. © International Association for Food Protection.