Patients with CF lung disease are susceptible to chronic infections by
various pathogens, such as Pseudomonas aeruginosa. This pathogen is
able to adaptat to the environment in CF lungs, characterized by
inflammatory defences, oxygen restriction, and poor nutrient availability. It
is well established that, once P. aeruginosa infection is installed in the
lungs, it is almost impossible to eradicate, due to sophisticated genotypic
and phenotypic adaptation mechanisms that develop according to the
stage of infection. Understanding those changes and the identification of
specific characteristics that allow P. aeruginosa eradication before the
onset of chronic infection is urgent. In this work, P. aeruginosa adaptation
under microaerophilic and anaerobic conditions was assessed in terms of
phenotypic charatceristics, antibiotic susceptibility and expression of
antibiotic resistance mechanisms (mexAB operon). Results showed,
when compared with aerobic conditions, similar growth and emergence of
intermediate resistance profiles for ciprofloxacin and imipenem, but no
significant variation in operon mexAB expression. It was also observed an
increase of colony morphotypes with the decrease of oxygen availability,
mainly in 5% O2. Nevertheless oxygen depletion has no significant effect
on P. aeruginosa growth and mexAB expression, affecting, however, the
phenotypic characteristics and antibiotic susceptibility profiles. Despite
the overall observations, the microaerophilic environment with 5% O2,
seems to demonstrate a transient distinct behaviourwhich can be a point
of evolution into chronic infection and as such a possible treatment target
