Abstract
BackgroundMajority of enteric infections are foodborne and antimicrobials including antibiotics have been used for their control and treatment. However, probiotics or prebiotics or their combination offer a potential alternative intervention strategy for improving the host health and preventing foodborne pathogen colonization/infections in reservoir. Further, bioengineered probiotics expressing bioactive products to achieve specific function is highly desirable. Recently, we over-expressed mcra (myosin cross-reactive antigen) gene in Lactobacillus casei (Lc) and developed a bioengineered probiotics Lc + CLA which produce higher amounts of metabolites including conjugated linoleic acid (CLA). Furthermore, we also reported that prebiotic like components such as berry pomace (byproduct) phenolic extracts (BPEs) can enhance the growth of probiotics and improved the beneficial effects of probiotics. In this study, we evaluated the antimicrobial effect of modified Lc + CLA in combination of BPEs on growth, survival and pathogenesis of enterohemorrhagic Escherichia coli (EHEC).ResultsIn mixed culture condition, the growth of EHEC was significantly reduced in the presence Lc + CLA and/or BPEs. Cell-free cultural supernatant (CFCS) collected from Lc or Lc + CLA strain also inhibited the growth and survival of EHEC and the inhibitory effects of CFCSs against EHEC were enhanced in the presence of BPEs in concentration dependent manner. Interaction between EHEC and intestinal epithelial INT-407 cells were also altered significantly in the presence of either Lc or Lc + CLA strain or their CFCSs with or without BPEs. The expression of multiple virulence genes and physicochemical properties of EHEC were also altered when the bacterial cells were pretreated with CFCSs and/or BPEs.ConclusionsThese results showed that diet containing bioactive Lc + CLA and natural prebiotic like component such as BPEs might be an effective way to prevent foodborne infections with EHEC.
Highlights
Majority of enteric infections are foodborne and antimicrobials including antibiotics have been used for their control and treatment
Growth inhibition of Escherichia coli (EHEC) in presence or absence of probiotic strains and/or pomace phenolic extracts To determine the effect of prebiotic like component berry pomace phenolic extract (BPE), probiotic strain Lactobacillus casei (Lc) or Lc + conjugated linoleic acid (CLA) or the metabolites produced by Lc or Lc + CLA in Cell-free cultural supernatant (CFCS) on the growth inhibition of EHEC, we co-cultured EHEC with Lc or Lc + CLA or their CFCSs with different concentrations of BPEs [0.1 mg/ml gallic acid equivalent (GAE) or 0.5 mg/ ml GAE or 1.0 mg/ml GAE]
Either probiotic strain, Lc or Lc + CLA in combination with 0.1 mg/ ml GAE or 0.5 mg/ml GAE or 1.0 mg/ml GAE of BPEs intensified the reduction of the growth of EHEC in a time dependent manner but the inhibitory effect of Lc + CLA in presence of 1.0 mg/ml GAE was observed at maximum level [> 8.0 logs colony forming unit (CFU)/ml reduction] than the other treatments (Fig. 1C)
Summary
Growth inhibition of EHEC in presence or absence of probiotic strains and/or pomace phenolic extracts To determine the effect of prebiotic like component BPEs, probiotic strain Lc or Lc + CLA or the metabolites produced by Lc or Lc + CLA in CFCSs on the growth inhibition of EHEC, we co-cultured EHEC with Lc or Lc + CLA or their CFCSs with different concentrations of BPEs [0.1 mg/ml gallic acid equivalent (GAE) or 0.5 mg/ ml GAE or 1.0 mg/ml GAE]. Alteration of EHEC physicochemical properties in presence of BPEs and/or CFCSs collected from Lc or Lc + CLA We observed that pre-treatments of EHEC with all the treatments accept 0.1 mg/ml GAE of BPE, significantly increased the percentage of injured bacterial cells ranging from 36.33 to 58.97% when compared to control (without any treatments in growth media) (Table 1). BPEs in combination with CFCS-Lc or CFCS-Lc + CLA reduced the biofilm formation ability of EHEC when compared to the control group (growth media without treatment), significantly from < 1.0 log CFU/ml to > 4.4 logs CFU/ml and CFCS-Lc + CLA was more effective in the reduction of the biofilm formation in presence of same concentration of BPE in comparison with CFCS-Lc (Fig. 3A). We hypothesized that the ratio of injured bacterial cells depends on the anti-pathogenic metabolites present in the treatments
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