Activity of antibiotics against in vitro mono-species biofilms of P. aeruginosa and S. aureus in the context of cystic fibrosis : the influence of the culture medium

Cystic fibrosis is a genetic disease characterized by the accumulation of viscous mucus in the patient's airways, which favors bacterial colonization by bacterial communities named biofilms. The most common pathogens are Staphylococcus aureus in children and Pseudomonas aeruginosa in adults. Our goal was to develop a relevant artificial sputum medium (ASM) that can be used to grow biofilms of each of these bacteria and study the activity of antibiotics administered to the patients. We showed that the rheological properties of this medium were similar to those of sputa from patients. Biofilms from both species were less responsive to antibiotics in ASM than in a conventional medium. In addition, some antibiotics selected small colony variants in ASM, another mode of bacterial growth involved in the pathology. These results show the importance of using a relevant culture medium to study the activity of antibiotics in the context of this pathology.