Biology Reference
In-Depth Information
Disruption of quorum sensing was suggested as a new anti-infective
strategy, as a consequence of its importance in virulence development
in pathogenic bacteria (Finch et al., 1998). Several techniques have
been developed for this purpose, such as inhibition of signal molecule
biosynthesis, application of quorum sensing antagonists or agonistic
analogues, chemical or enzymatic inactivation and biodegradation of
quorum sensing molecules.
Disruption of quorum sensing might constitute an alternative
approach in aquaculture for preventing or combating infections caused by
pathogens that regulate virulence factor expression by a quorum sensing
system (Defoirdt et al., 2004). Halogenated furanones produced by the
marine red algae
Delisea pulchra
(Manefi eld et al., 1999) protected rotifers,
Artemia
and rainbow trout from the negative effect of vibrios when added
in adequate concentrations (Rasch et al., 2004; Defoirdt et al., 2006; Tihn
et al., 2007). Furanones show structural similarity with AHL molecules
and thus the mechanism of action would be based on binding to LuxR
proteins (Manefi eld et al., 1999) present in pathogens as
V. harveyi
(Henke
and Bassler, 2004).
The introduction of potential probiotic bacteria able to degrade quorum
sensing molecules might be useful as a biocontrol agent in aquaculture,
but the exploitation of these kind of bacteria remains a challenge for
future research (Tihn et al., 2008). It has been suggested that the positive
effect of
Bacillus
spp. strains used as probiotics in aquaculture (Moriarty,
1998; Rengpipat et al., 2003) might partly be due to inactivation of
quorum sensing molecules, apart from the production of antagonistic
substances (Dong et al., 2000; Molina et al., 2003; Dong et al., 2004). A
direct immunomodulatory activity was produced in several mammalian
systems by a quorum sensing molecule from
Pseudomonas aeruginosa
(Hooi
et al., 2004; Ritchie et al., 2005; Thomas et al., 2006).
The importance of quorum sensing
in situ
gene expression regulation
is becoming more evident for pathogenic bacteria, but hardly for putative
probiotic bacteria. Some problems could arise, such as the development of
resistances (Zhu et al., 1998), or lack of specifi city, as not all bacteria that
are found to contain quorum sensing systems are pathogens. Therefore,
we need to know more about the importance of quorum sensing molecules
on their
in vivo
metabolism and their interaction with the non-pathogenic
microbial community and with the host.
Acting on Host-Microbe Interactions
Immunostimulants
Fish are intimately in contact with a complex and dynamic microbial
world, and a large fraction of these microbes cling to and colonize epithelial
surfaces. In rare circumstances microbes cause disease, either directly, by
