Explorative gene analysis of antibiotic tolerance-related genes in adherent and biofilm cells of Pseudomonas aeruginosa.

Background: Antibiotic tolerance has attracted worldwide attention, as it leads to chronic, refractory, and persistent infections that are difficult to control. Bacterial biofilms are well known to be more tolerant to antibiotics compared to planktonic bacteria. We previously revealed that adherent bacteria on a solid surface also exhibited tolerance to antibiotics before forming a biofilm. However, little is known about the mechanisms of antibiotic tolerance for adherent or biofilm cells.

Objectives: We investigated the mechanisms of antibiotic tolerance in the biofilm life cycle using adherent and biofilm cells, and evaluated the possibility that common mechanisms operate at each stage.

Methods: We constructed transposon mutants of Pseudomonas aeruginosa PAO1 and screened for low-tolerant mutants with two different methods, using adherent cells and biofilm cells.

Results: Fourteen and nine mutants exhibiting low antibiotic tolerance were detected in the adherent cells and biofilm cells, and 14 and 7 candidate genes linked to this tolerance were identified by sequencing, respectively. Eight of the 14 genes related to the antibiotic tolerance of the adherent cells were involved in biofilm formation. Two of the seven genes related to the antibiotic tolerance of biofilm cells participated in the antibiotic tolerance of adherent cells.

Conclusions: The antibiotic tolerance of adherent cells and biofilm formation appear to be under the same regulation mechanism to promote survival in the presence of antibiotics. Antibiotic tolerance shows a complex regulation mechanism at each stage of biofilm formation.