Differential expression of virulence and stress fitness genes during interaction between Listeria monocytogenes and Bifidobacterium longum

Bifidobacterium is well known to have an inhibitory effect on the survival, growth, and proliferation of various foodborne pathogens, but the mechanism of the molecular action of B. longum in blocking the invasion of Listeria monocytogenes is not yet well defined. In the present study, following RNA extraction and cDNA synthesis, differential expression of virulence and stress fitness genes in L. monocytogenes and B. longum was determined by real-time PCR. The results indicate that L. monocytogenes virulence factors, including actA, hly, inlA, and plcA, showed significantly downregulated expression during co-incubation of B. longum and L. monocytogenes in phosphate-buffered saline. The relative mRNA levels of oppA and serpin, two stress fitness genes in B. longum, were significantly higher than for the control group. These results indicate that downregulation of L. monocytogenes virulence factors during co-incubation with B. longum might be responsible for the inhibitory effects.