Effect of Incubation Temperature and Human Serum on Yeast to Hyphal Morphogenesis in Vaginal Candida albicans and its Correlation to Virulence Markers

Aims: To investigate the effect of human serum, starvation and /or variation in incubation temperature on yeast and pseudo-hyphae and/ or hyphal cell differentiation in vaginal Candida albicans strains and, its correlation to exoenzymes productivity.

Study Design: A total of 31 C. albicans strains previously isolated from high vaginal swab specimens of pregnant Saudi women, as well as the C. albicans QC strain ATCC 10231 were recruited from Brain Heart Infusion-glycerol stock cultures(-80ºC) & included in the study.

Place and Duration of Study: Department of Clinical Laboratory Sciences, College of Applied Medical Sciences, King Saud University, Riyadh, Saudi Arabia, between September 2013 and December 2013.

Methodology: Each of thirty one vaginal C. albicans strains and the QC strain (ATCC 10231) was grown in Modified Sabouraud Broth (MSB) at 25ºC and at 37ºC with or without addition of 20 % human serum; and morphological growth was observed at 2 hours intervals by phase contrast microscopy. Selected C. albicans strains that showed ability and/or weak-ability of yeast-hyphal transition were also tested for their exo-hydrolytic enzymes of phospholipase, and proteinase as caseinase, & gelatinase, and coagulase, virulence markers.

Results: Showed that at 25ºC 28/31(90.3%) strains were non filamentous, 3/31(9.6%) strains were moderately filamentous, and 0.0% strong filamentous, in comparison, at 37ºC those numbers were 19/31(61.3%), 10/31(32.3%), and 2/31 (6.4%) respectively, suggesting that mere increase in temperature from 25ºC to 37ºC remarkably increases yeast morphogenesis to filamentous forms. Such increase was significantly (P<0.001) more pronounced upon the addition of 20% serum at either incubation temperature of 25ºC or 37ºC as expected. Generally the presence of serum and/or incubation at high temperature (37ºC), speeds off hyphal growth formation. Additionally, results also showed that 8/31 (25.8%) strains exhibited transition to hyphal forms only in presence of serum, whereas 7/31 (22.6%), apparently lost their capacity to switch to hyphal forms even in presence of serum and/or at temperature of 37ºC incubation. In contrast three strains 3/31, (9.7%) expressed such ability of filamentous growth in presence or absence of serum at 37ºC as well as 25ºC. These strains also showed enhanced secretion of exoenzymes. Therefore, these strains would be the most virulent ones. Whereas those strains (7/31, 22.6%) that did not show filamentous growth at any of the examined growth conditions would be considered as less virulent strains. However, considering the limited number of strains tested in this study, these findings require further substantiation by large sample size and in vivo animal studies.

Conclusion: Results obtained suggest that vaginal C. albicans strains are heterogenous in their potency to switch from yeast to hyphae. Strains which show morphogenesis in absence of serum and/or at low temperature (25ºC) exhibit higher exoenzymes activity suggesting that these strains are more pathogenic