Real-time Imaging and Quantification of Fungal Biofilm Development Using a Two-Phase Recirculating Flow System

Summary

We describe the assembly, operation, and cleaning of a flow apparatus designed to image fungal biofilm formation in real time while under flow. We also provide and discuss quantitative algorithms to be used on the acquired images.

Abstract

In oropharyngeal candidiasis, members of the genus Candida must adhere to and grow on the oral mucosal surface while under the effects of salivary flow. While models for the growth under flow have been developed, many of these systems are expensive, or do not allow imaging while the cells are under flow. We have developed a novel apparatus that allows us to image the growth and development of Candida albicans cells under flow and in real-time. Here, we detail the protocol for the assembly and use of this flow apparatus, as well as the quantification of data that are generated. We are able to quantify the rates that the cells attach to and detach from the slide, as well as to determine a measure of the biomass on the slide over time. This system is both economical and versatile, working with many types of light microscopes, including inexpensive benchtop microscopes, and is capable of extended imaging times compared to other flow systems. Overall, this is a low-throughput system that can provide highly detailed real-time information on the biofilm growth of fungal species under flow.

Introduction

Candida albicans (C. albicans) is an opportunistic fungal pathogen of humans that can infect many tissue types, including oral mucosal surfaces, causing oropharyngeal candidiasis and resulting in a lower quality of life for affected individuals¹. Biofilm formation is an important characteristic for the pathogenesis of C. albicans, and numerous studies have been done on the formation and function of C. albicans biofilms^2,3,4,5, many of which have been conducted using static (no flow)....

Protocol

1. Assemble the Flow Apparatus

1. Configure the parts listed in the Table of Materials according to the schematic in Figure 1 with the considerations discussed below.
   NOTE: For convenience, the flow apparatus is divided into two sides, the green side (everything upstream of the slide to the media flasks), and the orange side (everything downstream of the slide to the media flasks).
   1. Ensure that all of the flow apparatus is air tight to prevent leak.......

Discussion

Using the flow system as outlined above allows for the generation of quantitative time-lapse videos of fungal biofilm growth and development. To allow for comparisons between experiments it is of critical importance to ensure that the imaging parameters are kept the same. This includes ensuring that the microscope is set up for Köhler illumination for each experiment (many guides are available online for this process). Aside from imaging parameters, there are some important steps to keep in mind when working with th.......

Materials

Name	Company	Catalog Number	Comments
Pump	Cole Parmer	07522-20	6
Pump head	Cole Parmer	77200-60	6
Tubing	Cole Parmer	96410-14	N/A
Bubble trap adapter	Cole Parmer	30704-84	3
Bubble trap vacuum adapter for 1/4” ID vacuum line	Cole Parmer	31500-55	3
In-line filter adapter (4 needed)	Cole Parmer	31209-40	8,9
Orange-side Y	Cole Parmer	31209-55	7
Green-side Y	ibidi	10827	2
* Slides	ibidi	80196	4
* Slide luers	ibidi	10802	4
Vacuum assisted Bubble trap	Elveflow/Darwin microfluidics	KBTLarge - Microfluidic Bubble Trap Kit	3
Media flasks	Corning	4980-500	1
0.2 µm air filter	Corning	431229	1
Threaded glass bottle for PD and filter flask (2 needed)	Corning	1395-100	5,10
Ported Screw cap for PD and filter flask (2 needed)	Wheaton	1129750	5,10
Screwcap tubing connector	Wheaton	1129814	5,10
Tubing connector beveled washer	Danco	88579	5,10
Tubing connector flat washer	Danco	88569	5,10
Clamps for in-line filters and downstream Y (7 needed)	Oetiker/MSC Industrial Supply Company	15100002-100	7,8,9
Clamp tool	Oetiker/MSC Industrial Supply Company	14100386	N/A
20 micron in-line media filter	Analytical Scientific Instruments	850-1331	8
10 micron in-line media filter	Analytical Scientific Instruments	850-1333	9
2 micron inlet media filter	Supelco/Sigma-Aldrich	58267	10
* 0.22 µm media filter	Millipore	SVGV010RS	11
* 0.22 µm media filter “adapter”	BD Biosciences	329654	11
Rubber stopper	Fisher Scientific	14-131E	1
Hotplate stirrer with external probe port	ThermoFisher Scientific	88880006	N/A
Temperature probe	ThermoFisher Scientific	88880147	N/A