Can a bacterium express a virulence gene and not produce toxins and what may be the cause of this?

Question

I am preparing a seminar on viable but non-culturable (VBNC) state in bacteria, mainly foodborne pathogens and I just saw this line in a journal article by Lothigius et al that "the expression of the virulence gene in VBNC cells does not necessarily indicate the cells will produce toxins". Any explanation on what this statement means?

Lothigius, Å., Sjöling, Å., Svennerholm, A.-M., & Bölin, I. (2010). Survival and gene expression of enterotoxigenicEscherichia coliduring long-term incubation in sea water and freshwater. Journal of Applied Microbiology, 108(4), 1441–1449.

Answer 1

To expand a bit on @Mohamed's answer, there are several mechanisms by which virulence gene products can be up- or down-regulated without changes to mRNA expression.

Post-translational modifications

Adenylate cyclase-hemolysin (AC-Hly) is a toxin produced by the Bordetella pertussis, the causal agent of whooping cough. There are very few amino acid differences between the AC-Hly of B. pertussis and closely related Bordetella species. Palmitoylations of lysine residues on the C-terminus of the B. pertussis AC-Hly are necessary for its specific cytotoxic activity. [Bouchez 2017]

RNA secondary structures

After transcription, mRNAs can form secondary structures by base pairing, preventing ribosome binding and translation. For some pathogens, virulence gene mRNAs forms these structures, which melt at human body temperature, allowing for fast production of toxins without the need to increase virulence gene transcription. [Narberhaus 2010]

Answer 2

Gene expression means making mRNA and then translated to protein. Their might be many steps unders regulation in this path where a gene makes mRNA but then that mRNA is not translated (like degraded or inactivated).