Inhibitory effect of lactobacilli supernatants on biofilm and filamentation ofC. albicans, C. tropicalis, andC. parapsilosis

AbstractProbioticLactobacillusstrains had been investigated for the potential to protect against infection caused by the major fungal pathogen of human,Candida albicans. Besides antifungal activity, lactobacilli demonstrated a promising inhibitory effect on biofilm formation and filamentation ofC. albicans. On the other hand, two commonly isolated non-albicansCandidaspecies,C. tropicalisandC. parapsilosis, have similar characteristics in filamentation and biofilm formation withC. albicans. However, there is scant information of the effect of lactobacilli on the two species. In this study, biofilm inhibitory effects ofL. rhamnosusATCC 53103,L. plantarumATCC 8014, andL. acidophilusATCC 4356 were tested on the reference strainC. albicansSC5314 and six bloodstream isolated clinical strains, two each ofC. albicans, C. tropicalis, andC. parapsilosis. Cell-free culture supernatants (CFSs) ofL. rhamnosusandL. plantarumsignificantly inhibitedin vitrobiofilm growth ofC. albicansandC. tropicalis. L. acidophilus, conversely, had little effect onC. albicansandC. tropicalisbut was more effective on inhibitingC. parapsilosisbiofilms. NeutralizedL. rhamnosusCFS at pH 7 retained the inhibitory effect, suggesting that exometabolites other than lactic acid produced by theLactobacillusstrain might be accounted for the effect. Furthermore, we evaluated the inhibitory effects ofL. rhamnosusandL. plantarumCFSs on the filamentation ofC. albicansandC. tropicalisstrains. Significantly lessCandidafilaments were observed after co-incubating with CFSs under hyphae-inducing conditions. Expressions of six biofilm-related genes (ALS1, ALS3, BCR1, EFG1, TEC1, andUME6inC. albicansand corresponding orthologs inC. tropicalis) in biofilms co-incubated with CFSs were analyzed using quantitative real-time PCR. When compared to untreated control, the expressions ofALS1, ALS3, EFG1, andTEC1genes were downregulated inC. albicansbiofilm. InC. tropicalisbiofilms,ALS3andUME6were downregulated whileTEC1was upregulated. Taken together, theL. rhamnosusandL. plantarumstrains demonstrated an inhibitory effect, which is likely mediated by the metabolites secreted into culture medium, on filamentation and biofilm formation ofC. albicansandC. tropicalis. Our finding suggested an alternative to antifungals for controllingCandidabiofilm.