Creation of these fusions allows quantification of virulence
gene expression as a simple enzyme assay. Construction
of hilALacZY Salmonella fusion strains has been
used to study and elucidate many of the factors responsible
for induction of these key regulatory components
(Bajaj et al., 1995, 1996). However, in situ application of
these fusion strains is less feasible as these strains are no
longer capable of synthesizing functional virulence genes.
In addition, for some fusion strains such as the β-galactosidase
constructs, there is a risk that lactose using nonsalmonellae
background microflora would also be capable
of synthesizing β-galactosidase enzyme and, thus, masking
the amount synthesized in vivo by the fusion strain.
Consequently, for effective in vivo examination of individual
virulence gene expression, more direct quantitative
measurement of gene response is required. Ideally,
monitoring instantaneous fluctuations of individual
genes as they are induced would provide a more realistic
picture of foodborne pathogen response during exposure
to food and feed processing conditions and possible antimicrobial
amendments.