<i>Candida albicans</i> enhances meropenem tolerance of <i>Pseudomonas aeruginosa</i> in a dual-species biofilm

BackgroundPseudomonas aeruginosa isan opportunistic bacterium that infects the airways of cystic fibrosispatients, surfaces of surgical and burn wounds, and indwelling medical devices.Patients are prone to secondary fungal infections, with Candida albicans beingcommonly co-isolated with P. aeruginosa. Both P. aeruginosa and C.albicans are able to form extensive biofilms on the surfaces of mucosa andmedical devices.ObjectivesTo determine whether the presence of C. albicans enhancesantibiotic tolerance of P. aeruginosa in a dual-species biofilm.MethodsSingle- and dual-species biofilms were established inmicrotitre plates and the survival of each species was measured followingtreatment with clinically relevant antibiotics. Scanning electron microscopyand confocal microscopy were used to visualize biofilm structure.ResultsC. albicans enhances P. aeruginosa biofilmtolerance to meropenem at the clinically relevant concentration of 5 mg/L. Thiseffect is specific to biofilm cultures and is dependent upon C. albicans extracellularmatrix polysaccharides, mannan and glucan, with C. albicans cellsdeficient in glycosylation structures not enhancing P. aeruginosa toleranceto meropenem.ConclusionsWe propose that fungal mannan and glucan secreted into theextracellular matrix of P. aeruginosa/C. albicans dual-speciesbiofilms play a central role in enhancing P. aeruginosa tolerance tomeropenem, which has direct implications for the treatment of coinfectedpatients.