Objective: Polymicrobial biofilms consisting of a combination of various bacteria and/or fungi are generally much more resistant than monomicrobial biofilms formed by these species alone. In this study, it was aimed to investigate how Candida albicans biofilms were affected in the presence of Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii or Pseudomonas aeruginosa or supernatants of these bacteria.

Method: C. albicans with Gram-negative polymicrobial biofilms were formed on sterile microplates by using control strains of C. albicans SC 5314, E. coli ATCC 25922, K. pneumoniae ATCC 700603, A. baumannii ATCC 19606 and P. aeruginosa PA01. The number of C. albicans in biofilms was determined in the presence of both Gram- negative bacteria and sterile supernatants.

Results: According to our results, all Gram negative bacteria displayed an antagonist effect against C. albicans in the biofilm and a three log decrease was observed compared to the control. Sterile supernatants were shown to have an inhibitory effect on the C. albicans biofilms and reduce the number of yeasts by at least one log. MTT assay and fluorescence microscopy images also confirmed the results.

Conclusion: In C. albicans-Gram-negative polymicrobial biofilms that can occur in many infections, bacteria affected C. albicans biofilm cells as antagonist agents, both with their cells and sterile cell-free supernatants.