Bacterial Pathogenesis, Molecular Basis of
571
in multicellular, sessile, and encapsulated
communities known as bioflms. Evidence
indicates that bacteria in the bioflm mode
oF growth exhibit increased resistance
to antimicrobial agents. It is not clear
whether the resistance is due to a combina-
tion oF the various mechanisms described
earlier, the Fact that the bioflm in en-
closed in a matrix oF extracellular material,
or specifc physiological changes occur-
ring within the organisms that elicit as-yet
undiscovered resistance mechanisms.
As we have seen in previous sections
oF this chapter, the Facility with which
bacteria can exchange genetic inForma-
tion allows For the acquisition oF many
traits by sometimes-unrelated organisms.
Such genetic-transFer mechanisms are also
important For the bacteria to acquire an-
timicrobial resistance.
7
Closing Remarks
As has been briefly outlined above, bacte-
rial pathogenesis involves a large, complex
interplay oF regulatory networks and viru-
lence Factors to allow pathogens to inhabit
their hosts and cause disease. This in-
terplay between host and bacteria has
resulted in many pathogens becoming
specifc For certain host species as they
evolve to profciently colonize and invade
the host. The transFer oF various viru-
lence genes between pathogenic species
increases the ftness oF pathogen popula-
tions and allows them to survive in an
increasing number oF hosts and special-
ized niches. Pathogens adapt to changes
in their environment by being able to
sense changes in their hosts and respond
by producing virulence Factors that aid
in their survival. As one might imagine,
these adaptations require an intricate bal-
ance oF the expression oF certain genes.
±
o
rs
om
eo
Ft
h
ev
i
r
u
l
e
n
c
eF
a
c
t
o
r
s
,d
e
-
tails regarding the mechanisms and ge-
netics have been elucidated. In many
cases, the genetic regulation is poorly
understood. While we have made great
progress in characterizing the molecular
basis oF pathogenesis, we cannot defne
the Full complement oF Factors required
For pathogenicity. The advent oF new
technologies such as DNA microarrays
combined with the sequencing oF ever-
increasing numbers oF bacterial genomes
is allowing For the comparison oF gene
complements and genetic expression be-
tween organisms. Many common products
and motiFs have been discovered between
pathogenic organisms and these observa-
tions are increasing the pace with which
the molecular mechanisms oF pathogen-
esis can be and are being deciphered.
Nonetheless, studies oF the array oF prod-
ucts and strategies that bacterial pathogens
use to survive within their hosts are always
revealing novel and surprising fndings
that illustrate the complexity that is bacte-
rial pathogenesis.
See also
Bacterial Growth and Di-
vision;
E. Coli
Genome; Genetics,
Molecular Basis oF.
Bibliography
Books and Reviews
DaFFe, M., Etienne, G. (1999) The capsule oF
Mycobacterium tuberculosis
and its implications
For
pathogenicity,
Tuberc.
Lung
Dis.
79
,
153–169.
±inlay, B.B., ±alkow, S. (1997) Common themes
in microbial pathogenicity revisited,
Microbiol.
Mol. Biol. Rev.
61
, 136–169.
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