Effects of human blood red cells on the haemolytic capability of clinical isolates of Candida tropicalis

BACKGROUND: Candida tropicalis is an increasingly important human pathogen associated with high mortality rates; however, little is known regarding the virulence properties of C. tropicalis, particularly the production of haemolytic factor. Although Candida spp may acquire iron from human blood red cells (RBCs) by producing a haemolytic factor that promotes cell lyses, at present there are no data regarding the effect of RBCs on the production of haemolytic molecules. The present study was undertaken to evaluate the role of human red blood cells on the production haemolytic factor by C. tropicalis; in addition, the transcription levels of a putative haemolysin-like protein gene (HLPt) were also analysed. RESULTS: C. tropicalis isolates produced a haemolytic factor following growth in either the absence or presence of RBCs; however, distinct levels of haemolysis were observed, with 60% of the isolates exhibiting a significant increase in the production of haemolytic factor when grown in the presence of human RBCs. All isolates in which the putative HLPt gene was up-regulated in presence of human RBCs, ranging from 1.044 to 6.965-fold, also exhibited higher haemolytic activity following growth in the presence of RBCs compared to that observed in the absence of RBCs. CONCLUSIONS: We propose that human RBCs may induce changes in the phenotypic expression of haemolytic factor and in transcriptional levels of the putative C. tropicalis HLPt gene in an isolate-dependent fashion.