Résumé
The use of bacteriophages against pathogenic bacteria in health care and
in the food industry is now being advocated as an alternative to the use
of antibiotics. But what is the evolutionary response for a bacterial
population if both antibiotics and phages are used in combination? We
employ an experimental evolution approach to address these questions and
exposed Pseudomonas fluorescens SBW25 and a related hypermutator strain
(mutS-) to the action of the antibiotic rifampicin and the lytic
bacteriophage SBW25φ2. We then compared the densities, growth rates, and
the mutations at the rpoB locus leading to rifampicin resistance of the
evolved bacterial populations. We observed that the evolutionary response
of populations under different treatments varied depending on the order in
which the antimicrobials were added and whether the bacterium was a
hypermutator. We found that wild type rifampicin-resistant populations
involved in biofilm formation often reverted to rifampicin sensitivity
when stresses were added sequentially. In contrast, when the mortality
agents were added simultaneously, phage populations frequently went
extinct and the bacteria evolved antibiotic resistance. Finally,
populations of the hypermutator mutS- converged to a single genotype at
the rpoB locus. Future investigation on other bacteria and using different
antibiotics and bacteriophage are needed to evaluate the generality of our
findings.