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Microbiol. Mol. Biol. Rev., 06 1997, 136-169, Vol 61, No. 2
BB Finlay and S Falkow
Bacterial pathogens employ a number of genetic strategies to cause
infection and, occasionally, disease in their hosts. Many of these
virulence factors and their regulatory elements can be divided into a
smaller number of groups based on the conservation of similar mechanisms.
These common themes are found throughout bacterial virulence factors. For
example, there are only a few general types of toxins, despite a large
number of host targets. Similarly, there are only a few conserved ways to
build the bacterial pilus and nonpilus adhesins used by pathogens to adhere
to host substrates. Bacterial entry into host cells (invasion) is a complex
mechanism. However, several common invasion themes exist in diverse
microorganisms. Similarly, once inside a host cell, pathogens have a
limited number of ways to ensure their survival, whether remaining within a
host vacuole or by escaping into the cytoplasm. Avoidance of the host
immune defenses is key to the success of a pathogen. Several common themes
again are employed, including antigenic variation, camouflage by binding
host molecules, and enzymatic degradation of host immune components. Most
virulence factors are found on the bacterial surface or secreted into their
immediate environment, yet virulence factors operate through a relatively
small number of microbial secretion systems. The expression of bacterial
pathogenicity is dependent upon complex regulatory circuits. However,
pathogens use only a small number of biochemical families to express
distinct functional factors at the appropriate time that causes infection.
Finally, virulence factors maintained on mobile genetic elements and
pathogenicity islands ensure that new strains of pathogens evolve
constantly. Comprehension of these common themes in microbial pathogenicity
is critical to the understanding and study of bacterial virulence
mechanisms and to the development of new "anti-virulence" agents, which are
so desperately needed to replace antibiotics.
Copyright © 1997, American Society for Microbiology
Common themes in microbial pathogenicity revisited
Biotechnology Laboratory, University of British Columbia, Vancouver, Canada. bfinlay@unixg.ubc.ca
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