Effect of whey protein fermentation and hydrolysis on Listeria monocytogenes virulence gene expression in the presence of the gut microbiota modelled in the Simulator of the Human Intestinal Microbial Ecosystem
Virulence gene expression of the foodborne pathogen L. monocytogenes promotes invasion and spreading within a susceptible host, such as populations with weakened immunity, and can be modulated by protein. In this thesis, enzymatically hydrolysed proteins were shown to reduce actA expression of L. monocytogenes regardless of the source, whereas actA expression was increased by intact whey protein isolate (WPI) but unaffected by individual BCAA and fermented WPI. In simulated gastrointestinal conditions, F2365 showed poor acid tolerance compared to 16PF0833 and ILSI #39, whereas survival and gene expression was similar for the three strains in response to bile and the PC metabolome in the presence of WPI, hydrolysed WPI, or casamino acids. Regardless of the strain and protein treatment, expression was induced for the virulence gene regulator prfA and internalins. The low expression of late-stage virulence genes (hly, plcA, actA) during gastrointestinal stress suggests low PrfA protein activity in these conditions.