7 research outputs found
Boundary-Value Problems of the Dynamic Behavior of Two-Dimensional Elastic Systems with Moving Objects
Within-host evolution decreases virulence in an opportunistic bacterial pathogen
Background: Pathogens evolve in a close antagonistic relationship with their hosts. The conventional theory
proposes that evolution of virulence is highly dependent on the efficiency of direct host-to-host transmission. Many
opportunistic pathogens, however, are not strictly dependent on the hosts due to their ability to reproduce in the
free-living environment. Therefore it is likely that conflicting selection pressures for growth and survival outside
versus within the host, rather than transmission potential, shape the evolution of virulence in opportunists. We
tested the role of within-host selection in evolution of virulence by letting a pathogen Serratia marcescens db11
sequentially infect Drosophila melanogaster hosts and then compared the virulence to strains that evolved only in
the outside-host environment.
Results: We found that the pathogen adapted to both Drosophila melanogaster host and novel outside-host
environment, leading to rapid evolutionary changes in the bacterial life-history traits including motility, in vitro
growth rate, biomass yield, and secretion of extracellular proteases. Most significantly, selection within the host led
to decreased virulence without decreased bacterial load while the selection lines in the outside-host environment
maintained the same level of virulence with ancestral bacteria.
Conclusions: This experimental evidence supports the idea that increased virulence is not an inevitable
consequence of within-host adaptation even when the epidemiological restrictions are removed. Evolution of
attenuated virulence could occur because of immune evasion within the host. Alternatively, rapid fluctuation
between outside-host and within-host environments, which is typical for the life cycle of opportunistic bacterial
pathogens, could lead to trade-offs that lower pathogen virulence.peerReviewe