Physical Disruption and Antibiotic Treatment of Pseudomonas aeruginosa with Gentamicin and Ciprofloxacin Biofilms has No Effect on the Proportion of Rough Small Colony Variants

Pseudomonas aeruginosa is an opportunistic pathogen, armed with multiple resistance mechanisms that render it resistant to many antibiotics. One such mechanism is the ability to form biofilms. A previous study assessed the viability of P. aeruginosa cells within biofilms after physical disruption and antibiotic treatment, and found that there was no difference in cell viability despite physical disruption. However, an increase in green color, thought to be pyocyanin, was observed at higher amounts in the biofilms that had been exposed to both stresses. The purpose of this study was to determine if the lack of change in cell viability during antibiotic treatment and physical disruption was due to an increase in rough small colony variants of P. aeruginosa. The relative proportions of these variants within biofilms were assessed by quantitatively measuring changes in pyocyanin and qualitatively measuring pilin production over a 4-hour antibiotic treatment period following disruption compared to undisrupted biofilms. Antibiotic treatment caused an equal decrease in cell viability, regardless of biofilm disruption, indicating that physical disruption of biofilms was not sufficient to increase susceptibility to antibiotic treatment. Additionally, the results of the pyocyanin and pilin assays showed no relative change between the antibiotic treatment and/ or biofilm disruption conditions over the course of treatment. Therefore, no supporting evidence was generated for the hypothesis that P. aeruginosa within biofilms respond to physical disruption and antibiotic stress by increasing the proportion of rough small colony variants.