WS02.8 Altered therapeutic susceptibility of mucoid Pseudomonas aeruginosa in artificial sputum medium

Abstract

Objectives The relevance of antimicrobial susceptibility testing of Pseudomonas aeruginosa isolates from cystic fibrosis (CF) patients has recently come into question as the traditional in vitro test conditions used have little in common with the in vivo environment. To improve our understanding of mucoid P. aeruginosa infection in the CF lung, an artificial sputum medium (AS) was used to mimic the nutritional environment in CF sputum. OligoG, a low molecular weight alginate oligomer, is a novel therapeutic that has been shown to disrupt pseudomonal biofilms and potentiate antibiotic effects. Its therapeutic effect in an environment mimicking the lung however has not previously been tested. Methods Growth curves and susceptibility testing of colistin +/– OligoG of the CF clinical isolate Pseudomonas aeruginosa NH53788A were compared in Mueller-Hinton broth (MH) and AS. Anti-biofilm effects were visualised using LIVE/DEAD® confocal laser scanning microscopy (CLSM) and scanning electron microscopy. Results CLSM confirmed the dose-dependent biofilm disruption properties of OligoG, with an enhanced combined antimicrobial effect observed when tested in conjunction with colistin, characterised by cellular aggregation and decreased bacterial viability in MH. Growth in AS was considerably lower compared to MH, with minimum inhibitory concentrations (MICs) for colistin increased 4-fold (0.4 compared to 0.1 mg/L in MH). A dose dependent reduction in biofilm microcolony size was also seen when treated with OligoG in AS. Conclusion The contrasting results obtained in the individual medium reflect the role of local environment on the effectiveness of antimicrobial therapy.