Screening clinical Candida albicans isolates for invasiveness by mimicking the human environment

Candida albicans virulence is associated with filamentation, triggered by environmental factors encountered in the host. Here, we monitored the growth behaviour of C. albicans isolated from a patient's abscess. We also established an in vitro screening framework of filamentation to assess the invasiveness potential of 10 clinical isolates.

Routine microbiology testing and convenience sampling were used for patients' selection. We monitored the colony appearance time of one abscess isolate ex vivo using time-lapse imaging. Filamentation patterns of 10 isolates were followed >14 days using 48 variations of growth conditions (glucose and nitrogen concentrations, pH, and temperature) to mimic host environment fluctuations. An automated image analysis pipeline was developed to quantify filamentation. Filamentation was also tested by growing isolates on modified filtration membranes, mimicking physical human body barriers.

The abscess isolate displayed heterogeneous colony appearance times and filamentation morphologies, indicating phenotypic heterogeneity within a growing population. Filamentation of all isolates was growth parameter- and isolate-dependent. Based on their filamentation response to environmental changes, the isolates clustered into three distinct groups, reflecting their site of isolation in the host. Colony transmigration on modified filtration membranes was a predictor for filamentation on agar.

We observed diverse filamentation morphologies in all isolates, indicating a phenotypically heterogeneous behaviour. Using our newly established screening framework, we could group isolates based on their isolation site, showing a link between filamentation morphology and invasive potential of C. albicans isolates.