In our heyday, we host trillions of microbes in perfect harmony. But some of our resident microbes are opportunistic and can become potential threats, especially to infants, the elderly, and immunocompromised people. Thus, Candidiasis, caused by pathogenic fungi of the Candida family, is a major cause of infections in hospitalised patients undergoing immunosuppressive drug therapies. 

Candida infections are aggressive due to their ability to form slimy aggregates called biofilms. In the biofilm mode, they can colonise diverse surfaces, escape host defences, and even show enhanced resistance to targeted drugs by sequestering them. As a result, Candida biofilms can grow on medical devices, like vascular catheters, prosthetic heart valves, and joint prostheses. Left untreated, it leads to life-threatening whole-body infection requiring the removal of the devices as well. 

Biofilm research is mostly done in vitro, in artificial conditions for better control and ease of work. Nonetheless, it requires a close simulation of the natural environment. Anil Thakur, Assistant Professor, Regional Centre for Biotechnology, Faridabad, recently reported an in vitro method for culturing fungal pathogens of the Candida family on gelatin-coated coverslips. 

Candida auris is an emerging pathogen of global concern. Initially, the research group found that known growth platforms are not producing the ideal multi-layered biofilm of C. auris. So, the first challenge was to create the necessary platform that closely mimics human skin. Thakur says, ​“Existing research methods often fail to capture the full spectrum of biofilm development and its interaction with a human-like environment.”

Hence, driven by the compelling need to unravel the intricacies of C. auris biofilm formation, our journey began with the goal of introducing a robust methodology that mirrors the conditions C. auris encounters in the human host.

Following rigorous screening, they selected a gelatin-based platform with several advantages. Derived from bovine skin, gelatin closely mimics human skin without requiring the cumbersome biosafety permissions necessary for working with biological skin. Besides being cost-effective, it can interact with water — a desired quality absent in currently used materials. The method they reported is user-friendly. It involves limited handling which reduces the chance of technical errors and the need for expert hands. These qualities make the method robust and novel. It can thus speed up the entire process of large-scale screening experiments necessary for keeping a line-up of new drugs handy. 

Susan Thomas, Scientist, National Institute for Research in Reproductive and Child Health, Mumbai, studies Candida species to identify novel antifungal drug targets. She comments, ​“C. auris is one of the four fungal pathogens that has been classified by World Health Organisation as ​“critical” in the fungal priority pathogens list released last year. It is a major cause of hospital-acquired multidrug-resistant infections with high associated mortality.” 

Cost-effective, robust models that can mimic clinical biofilms can be immensely useful for the identification of novel therapeutics.

Biofilm researchers working with C. auris also notice varying colony characteristics with varying growth conditions and this heterogeneity was the second challenge to address. Thakur notes, ​“Our study needed to account for this variability while ensuring the reproducibility and consistency of our results and comprehensive understanding of C. auris biofilm heterogeneity and its implications for infection management.” He mentions that this also necessitated sophisticated imaging and analytical techniques to capture and analyse the subtle nuances of biofilm structure and development, pushing the boundaries of existing technological capabilities.

This study was done in collaboration with researchers from Gautam Buddha University, Greater Noida, and Indian Institute of Technology Delhi. Thakur notes, ​“With our collaborators, we have discussed the concepts, optimisation, and tweaking of the system that has helped us to make this substratum a success.” They further showed that the biofilms of other pathogenic Candida species like C. albicans and C. glabrata could be grown successfully by this method. This demonstrates the wider applicability of this approach in probing the defence strategies of pathogenic Candida species.