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

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