Acinetobacter baumannii does not affect Candida albicans Susceptibility to Fluconazole in vitro

Candida albicans is the most common human fungal pathogen and is difficult to treat due to the scarcity of and increasing resistance to fungicidal drugs. C. albicans is commonly isolated with bacterial pathogens such as Pseudomonas aeruginosa and Acinetobacter baumannii that also cause multidrug-resistant hospital-acquired infections. We have recently described how the presence of P. aeruginosa makes the antifungal drug fluconazole (FLC) more effective and switches it from fungistatic to fungicidal against C. albicans , a process sensitive to iron chelation. Although different P. aeruginosa isolates enhance fluconazole sensitivity, it is unknown if other bacterial species have a similar effect. A. baumannii is similar to P. aeruginosa : it is gram-negative, drug resistant, produces siderophores and causes intractable nosocomial infections. In this study, we investigated if A. baumannii has a similar bacterial-drug synergy against C. albicans . We found that A. baumannii shows little to no enhancement of FLC against C. albicans in vitro. Our work indicates that not all opportunistic bacterial pathogens have the same effect on Candida drug susceptibility as P. aeruginosa . It further suggests that P. aeruginosa produces unique molecules that drive its interactions with C. albicans and contribute to the clearance of C. albicans in the presence of FLC. This work addresses the need to understand how microbe-microbe interactions regulate virulence and antimicrobial susceptibility of fungal pathogens, a still poorly understood aspect of infection and colonization.