Bacterial lipopolysaccharides variably modulate in vitro biofilm formation of Candida species

Abstract

The objective of this study was to evaluate the effect of the bacterial endotoxin LPS onCandidabiofilm formationin vitro. The effect of the LPS ofPseudomonas aeruginosa,Klebsiella pneumoniae,Serratia marcescensandSalmonella typhimuriumon six different species ofCandida, comprisingCandida albicansATCC 90028,Candida glabrataATCC 90030,Candida kruseiATCC 6258,Candida tropicalisATCC 13803,Candida parapsilosisATCC 22019 andCandida dubliniensisMYA 646, was studied using a standard biofilm assay. The metabolic activity ofin vitro Candidabiofilms treated with LPS at 90 min, 24 h and 48 h was quantified by XTT reduction assay. Viable biofilm-forming cells were qualitatively analysed using confocal laser scanning microscopy (CLSM), while scanning electron microscopy (SEM) was employed to visualize the biofilm structure. Initially, adhesion ofC. albicanswas significantly stimulated byPseudomonasandKlebsiellaLPS. A significant inhibition ofCandidaadhesion was noted for the following combinations:C. glabratawithPseudomonasLPS,C. tropicaliswithSerratiaLPS, andC. glabrata,C. parapsilosisorC. dubliniensiswithSalmonellaLPS (P<0.05). After 24 h of incubation, a significant stimulation of initial colonization was noted for the following combinations:C. albicans/C. glabratawithKlebsiellaLPS,C. glabrata/C. tropicalis/C. kruseiwithSalmonellaLPS. In contrast, a significant inhibition of biofilm formation was observed inC. glabrata/C. dubliniensis/C. kruseiwithPseudomonasLPS,C. kruseiwithSerratiaLPS,C. dubliniensiswithKlebsiellaLPS andC. parapsilosis/C. dubliniensis/C. kruseiwithSalmonellaLPS (P<0.05). On further incubation for 48 h, a significant enhancement of biofilm maturation was noted for the following combinations:C. glabrata/C. tropicaliswithSerratiaLPS,C. dubliniensiswithKlebsiellaLPS andC. glabratawithSalmonellaLPS, and a significant retardation was noted forC. parapsilosis/C. dubliniensis/C. kruseiwithPseudomonasLPS,C. tropicaliswithSerratiaLPS,C. glabrata/C. parapsilosis/C. dubliniensiswithKlebsiellaLPS andC. dubliniensiswithSalmonellaLPS (P<0.05). These findings were confirmed by SEM and CLSM analyses. In general, the inhibition of the biofilm development of LPS-treatedCandidaspp.was accompanied by a scanty architecture with a reduced numbers of cells compared with the profuse and densely colonized control biofilms. These data are indicative that bacterial LPSs modulatein vitro Candidabiofilm formation in a species-specific and time-dependent manner. The clinical and the biological relevance of these findings have yet to be explored.