ABSTRACT
Stenotrophomonas maltophilia is a multidrug-resistant opportunistic pathogen. S. maltophilia quorum-sensing system is mediated by the diffusible signal factor (DSF), which synthesis depends on rpfF. It has been reported that rpfF disruption in S. maltophilia K279a leads to a loss of DSF synthesis, reduced levels of extracellular protease, swarming motility and virulence in the Galleria mellonella model. The aim of this work was to attain a deeper knowledge of the role of the rpf/DSF signalling system in S. maltophilia biofilm formation, phenotypic traits associated with biofilm development and virulence and antimicrobial susceptibility. To this end, comparative studies were conducted on S. maltophilia K279a and K279arpfF. The results presented here put in evidence the positive role of DSF in bacterial growth, biofilm formation, swimming and twitching motilities, DNAse, lipases and siderophores production as well as resistance to oxidative stress. Interestingly, DSF seems to be essential for the development of the spatially organised structure seen in mature biofilms. Therefore, DSF from S. maltophlia K279a positively regulates biofilm formation and virulence. Furthermore, DSF is necessary for the induction of L1 and L2 ß-lactamase production in K279a. This is the first evidence of the role of the rpf/DSF signalling system in S. maltophilia ß-lactam resistance.
Subject(s)
Bacterial Proteins/metabolism , Biofilms , Stenotrophomonas maltophilia/metabolism , Virulence Factors/biosynthesis , beta-Lactamases/metabolism , Animals , Bacterial Proteins/genetics , Gene Expression Regulation, Bacterial , Gram-Negative Bacterial Infections/microbiology , Humans , Moths/microbiology , Siderophores/metabolism , Stenotrophomonas maltophilia/genetics , Stenotrophomonas maltophilia/growth & development , Stenotrophomonas maltophilia/pathogenicity , Virulence , Virulence Factors/genetics , beta-Lactamases/geneticsABSTRACT
Stenotrophomonas maltophilia is a nosocomial pathogen of increasing importance. S. maltophilia K279a genome encodes a diffusible signal factor (DSF) dependent quorum sensing (QS) system that was first identified in Xanthomonas campestris pv. campestris. DSF from X. campestris is a homologue of farnesoic acid, a Candida albicans QS signal which inhibits the yeast-to-hyphal shift. Here we describe the antagonistic effects of S. maltophilia on C. albicans on filamentation as well as on its planktonic and biofilm modes of growth. To determine the role of the DSF-mediated quorum sensing system in these effects, C. albicans ATCC 10231 and C. albicans tup1 mutant, locked in the filamentous form, were grown with K279a or with its rpfF deletion mutant (DSF-). A significant reduction in viable counts of C. albicans was observed in planktonic cocultures with K279a as well as in mixed biofilms. Furthermore, no viable cells of C. albicans tup1 were recovered from K279a mixed biofilms. Fungal viability was also assessed by labeling biofilms with SYTO 9 and propidium iodide. Confocal images showed that K279a can kill hyphae and also yeast cells. Light microscopic analysis showed that K279a severely affects hyphae integrity. On the other hand, the presence of K279a rpfF did not affect fungal morphology or viability. In conclusion, we report for the first time that S. maltophilia interferes with two key virulence factors of C. albicans, the yeast-to-hyphal transition and biofilm formation. DSF could be directly responsible for these effects or may induce the gene expression involved in antifungal activity.
Subject(s)
Biofilms , Candida albicans/physiology , Hyphae , Plankton , Quorum Sensing , Stenotrophomonas maltophilia/physiologyABSTRACT
Stenotrophomonas maltophilia is a nosocomial pathogen of increasing importance. S. maltophilia K279a genome encodes a diffusible signal factor (DSF) dependent quorum sensing (QS) system that was first identified in Xanthomonas campestris pv. campestris. DSF from X. campestris is a homologue of farnesoic acid, a Candida albicans QS signal which inhibits the yeast-to-hyphal shift. Here we describe the antagonistic effects of S. maltophilia on C. albicans on filamentation as well as on its planktonic and biofilm modes of growth. To determine the role of the DSF-mediated quorum sensing system in these effects, C. albicans ATCC 10231 and C. albicans tup1 mutant, locked in the filamentous form, were grown with K279a or with its rpfF deletion mutant (DSF-). A significant reduction in viable counts of C. albicans was observed in planktonic cocultures with K279a as well as in mixed biofilms. Furthermore, no viable cells of C. albicans tup1 were recovered from K279a mixed biofilms. Fungal viability was also assessed by labeling biofilms with SYTO 9 and propidium iodide. Confocal images showed that K279a can kill hyphae and also yeast cells. Light microscopic analysis showed that K279a severely affects hyphae integrity. On the other hand, the presence of K279a rpfF did not affect fungal morphology or viability. In conclusion, we report for the first time that S. maltophilia interferes with two key virulence factors of C. albicans, the yeast-to-hyphal transition and biofilm formation. DSF could be directly responsible for these effects or may induce the gene expression involved in antifungal activity.
