Possibly in these
strains other virulence traits may compensate for the lack
of inhibitory capacity. Another possible explanation for the
lack of in vitro inhibitory phenotype is that expression of
the gene encoding for the growth-inhibiting phenomenon
can be down-regulated by certain signal transduction
systems or regulators (Dupuy and Matamouros, 2006). The
gene for the growth-inhibiting factor might also be located
on a plasmid and the absence of growth-inhibition may be
caused by the loss of this plasmid after in vitro cultivation
(Rood and Cole, 1991).