Adaptive resistance to antimicrobials has been widely reported in planktonic studied trough phenotypic
characterization and proteomic analysis. Concerning biofilm adaptation, the response of biofilm-entrapped
cells to chemical stress conditions is not yet well studied. There is evidence that proteins involved in oxidative
stress response, cell envelope synthesis, as well as in synthesis of EPS become up- or down-regulated in
biofilms, indicating that these altered phenotypes might contribute to antimicrobial tolerance. This work
aimed to examine whether exposure of Pseudomonas aeruginosa biofilms to benzalkonium chloride (BC) and
ciprofloxacin (CIP) could induce an adaptive response in bacteria. This was attained by inspection of proteome
alterations of the outer membrane (OMP) in biofilm cells. Biofilms were formed in 6-well plates for 24h being
after submitted to the presence of 0.9 mM BC and 6.0 ug/ml CIP, during 13 days. The obtained biofilm-cells were
separated and the OMP extracted. Protein patterns were analysed by 2-DE and gels by the SameSpot software.
Biofilm-proteome showed that P. aeruginosa adaptation to BC promoted the down-regulation of 36 OMP and
the up-regulation of only one. OMP 2DE of P. aeruginosa adapted to CIP revealed the down-regulation of 29
OMP. Six OMPs were changed in common by both antimicrobials, revealing a possible similar stress response.
Proteins identification is in progress. This study highlighted that there might be an OMP regulation when
bacteria within biofilms are submitted to chemical adaptation. This particular response to the environment can
be one of the causes of the well-known biofilm resistance phenotype
