Interactions between Candida and bacteria in polymicrobial biofilms

Research Summary: This study demonstrates that indwelling urinary catheters in ICU patients predominantly harbor polymicrobial biofilms. Flow-based assays revealed increased biofilm viability, thickness, and structural complexity compared to static conditions and mono-species biofilms.

Author interview: Purvi Joshi, a PhD student at The M. S. University of Baroda, researches on polymicrobial biofilms of Candida and bacteria using flow system to investigate virulence, antimicrobial resistance; and interactions with mammalian cells, including adhesion and invasion.

Linkedin – https://www.linkedin.com/in/purvi-joshi-9486ab1a9/

Twitter/X – https://x.com/purvijoshi_

Google Scholar- https://scholar.google.com/citations?user=gxY11ccAAAAJ&hl=en

Lab: Prof. Devarshi Gajjar, The Maharaja Sayajirao University of Baroda

Lab website: https://www.dgl-msubaroda.com/

What was the core problem you aimed to solve with this research?

The study was initially driven by a curiosity to investigate microbial colonization on catheters collected from ICU patients. Preliminary findings revealed that most catheters were colonized by multiple microbial species— a relatively under reported finding—majorly encountering complex polymicrobial communities comprising both fungal (Candida spp.) and bacteria. Recognizing the clinical significance and the relative lack of in-depth research on these polymicrobial interactions, especially under physiologically relevant flow conditions, we aimed to explore their biofilm-forming capabilities, virulence potential and impact on catheter-associated infections.

How did you go about solving this problem?

We started by collecting the catheters followed by isolating and identifying catheter microflora. This led to a very interesting observation regarding poly-microbial microflora. Later, after a few assays we selected the isolates for further studies- Candida albicans / Candida tropicalis each with either bacteria – K. pneumoniae / P. aeruginosa or E. coli. After studying biofilm under static condition, we wanted to mimic the biofilm formed under flow condition, hence established the flow system, which lead to the comparison between static and flow conditions.

How would you explain your research outcomes (Key findings) to the non-scientific community?

This article addresses the occurrence of polymicrobial biofilms on urinary catheters from ICU patients, particularly mixed Candida and bacterial colonisation. We studied their behaviour under dynamic (flow) conditions that mimic real physiological environments. Traditional studies often focus on mono-species colonization and static conditions, which fail to capture the complexity and clinical relevance of catheter biofilms.

Key findings:

1. Predominant Polymicrobial Colonization:

The majority of indwelling urinary catheters from ICU patients were colonized by polymicrobial biofilms, primarily involving Candida spp. and uropathogenic bacteria.

• Discrepancy Between Culture and Metagenomics:

Traditional culturing detected only a few organisms, while metagenomic analysis revealed a more diverse and complex microbial community.

• Enhanced Biofilm Formation in Co-cultures:

In vitro assays showed that Candida–bacteria combinations formed more robust and adherent biofilms compared to single-species biofilms.

• Flow Conditions Promote Biofilm Maturation:

Biofilms formed under flow conditions were thicker, more uniform and contained a higher proportion of viable cells than those formed under static conditions.

• Increased Pathogenic Potential of Polymicrobial Biofilms:

The structural complexity and viability of polymicrobial biofilms under flow suggest a greater risk of persistence, resistance, and infection severity in clinical settings.

“The coexistence of Candida and bacterial species in urinary catheter biofilms fosters a protective and cooperative environment, complicating treatment and contributing to persistent infections.”

What are the potential implications of your findings for the field and society?

This study proves to be a critical reporting of polymicrobial biofilms on urinary catheters. It could help in in-depth assessment of urinary catheters or urine cultures in case of complicated UTI.

This study highlights the clinical significance of polymicrobial biofilms on catheters, emphasizing the need for improved diagnostics and targeted therapies. Findings may lead to better infection management by in-depth assessment of urinary catheters or urine cultures in case of complicated UTI and improved patient outcomes.

What was the exciting moment during your research?

The entire study was completely new for me personally and in our lab as well. As these combinations are rarely studied, we had to trouble-shoot various aspects, but that I assume was the ‘exciting’ part of this study as it helped me and dissertation students learn a lot. The most amazing part was set-up of flow- be it the system or the flow rate. We had established the flow system from scratch using easily available and budget-friendly options- hence we used volumetric infusion pumps to maintain the flow, as they are precise in maintaining the flow rate and were a good alternative to peristaltic pumps usually used in flow systems. We replaced luer-adapters and silicone tubing with sterile one-time use IV sets, which served the purpose and were not very heavy on our pockets.

Paper reference: Joshi, P., Bhattacharjee, R., Sahu, M., & Gajjar, D. (2025). Insights into urinary catheter colonisation and polymicrobial biofilms of Candida-bacteria under flow condition. Scientific Reports, 15(1), 15375. (link – https://rdcu.be/ekoVq )

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