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Abstract
The primary cause attributed to decreased susceptibility of Pseudomonas aeruginosa to antibiotics is its ability to form dense, mucoid microbial communities known as biofilms, of which alginate is an important component. In this experiment we attempted to determine the point at which alginate becomes critical for reducing gentamicin susceptibility of P. aeruginosa PAO1 biofilms. We predicted that treatment of P. aeruginosa with alginate lyase would increase susceptibility, particularly in mature biofilms when alginate becomes a predominant biofilm component. Gentamicin susceptibility was tested on three strains, wild type PAO1, alginate overexpressing mutant Δ mucA, and underexpressing mutant Δ algA. Results showed that although antibiotic susceptibility decreased with increased growth, there was no significant difference between the lyase treated and control samples in any strain. No significant change in susceptibility was observed between wild type PAO1 and Δ mucA, but Δ algA exhibited a higher susceptibility within the 6 to 24 hour time frame. Using the wild type strain only, we showed that alginate concentration increased over time, although the alginate lyase treatment did not appear to have any effect. However, the concentration of reducing sugars showed a significantly higher increase in the enzyme treated biofilms, suggesting alginate degradation. Due to these conflicting results, we were unable to determine whether or not the lyase treatment was effective in decreasing the alginate concentration. Further experiments are required to either support or refute our hypothesis.