The Role of Alginate in P. aeruginosa PAO1 Biofilm Structural Resistance to Gentamicin and Ciprofloxacin

The formation of a biofilm by many opportunistic bacteria such as Pseudomonas aeruginosa has been shown to provide the bacteria with a form of protection from various environmental fluctuations. Biofilm formation through the excretion of an exopolysaccharide matrix has become particularly important in hospital settings where many Pseudomonas infections are resistant to commonly used antibiotics. This study investigated the role of alginate in biofilm structure as a protection mechanism in the ability to resist antibiotic killing by gentamicin and ciprofloxacin. Early and established biofilms were treated and incubated with gentamicin or ciprofloxacin alone and in combination with alginate lyase for four hours. After incubation, all biofilms were physically disrupted and used to carry out an antibiotic resistant plate assay. It was found that after one day of growth, the percent survival of P. aeruginosa after gentamicin treatment was 9%, which decreased to 5% when gentamicin treatment was combined with alginate lyase. After five days of growth, the percent survival was 31% after gentamicin treatment and 0% after treatment with gentamicin and alginate lyase. Correspondingly, after one day of growth, the percent survival of P. aeruginosa after treatment with ciprofloxacin was 100%, but decreased to 3% with the addition of alginate lyase. After five days of growth, P. aeruginosa had a 100% survival rate after ciprofloxacin treatment, but decreased to 0% after treatment in combination with alginate lyase. In conclusion, these results indicate that alginate plays a central role in biofilm resistance to antibiotic killing and it was found that alginate lyase increased bacterial death when used in combination with gentamicin and ciprofloxacin, and a more pronounced effect was seen with ciprofloxacin.