Figure 1. Confocal microscopy of a Streptococcus biofilm; live cells are green, dead cells are red. Magnification: 400x. Photo credit: Katherine Kennedy and Jessica Knoch, Faculty of Veterinary Medicine, University of Calgary.

Figure 2. Confocal microscopy of a Streptococcus biofilm showing film thickness in microns; live cells are green, dead cells are red. Photo credit: Katherine Kennedy and Jessica Knoch, Faculty of Veterinary Medicine, University of Calgary.

Biofilm Imaging

Published: August 24, 2022

Mastitis is a streptococcal infection of the bovine mammary gland that results in udder inflammation and reduced milk production (Zaatout, 2022). The Streptococcus bacterium evades the bovine immune system by multiplying, aggregating, and forming a microbial mat or biofilm (Hirschfield, 2014).

Mastitis biofilms are resistant to antibiotics, and for that reason they are troubling to dairy producers. In 2018, for instance, the cost of treating mastitis was $662 CAD per milking cow (Aghamohammadi et al., 2018).

This summer, while working as an NSERC student research assistant in the Faculty of Veterinary Medicine (University of Calgary), I imaged Streptococcus biofilms using confocal microscopy.

This technique allows the comparison of biofilm characteristics - such as cell viability, cell distribution, and film thickness - across streptococcal biovars.

By treating the microbial mats with fluorescent dye, I demonstrated that biofilms are composed of both live and dead cells (Figure 1).

Interestingly, the dead-cell component of these microbial mats is important: While undergoing apoptosis, dying cells release genomic DNA that enhances biofilm adhesion, durability, and thickness (Figure 2; Bayles, 2007; Wingender et al., 1999).

Literature Cited

Aghamohammadi, M., Haine, D., Kelton, D. F., Barkema, H. W., Hogeveen, H., Keefe, G. P., & Dufour, S. (2018). Herd-level mastitis-associated costs on Canadian dairy farms. Frontiers in Veterinary Science, 5(100), 1-12. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5961536/#:~:text=Mastitis%20costs%20were%20substantial%20

Bayles, K.W. (2007). The biological role of death and lysis in biofilm development. Nature Review Microbiology, 5(9), 721-726. https://pubmed.ncbi.nlm.nih.gov/17694072/#:~:text=Following%20cell%20death%2C%20a%20sub,intercellular%20adhesion%20and%20biofilm%20stability

Hirschfield, J. (2014). Dynamic interactions of neutrophils and biofilms. Journal of Oral Microbiology, 6(1), 1-10. https://www.tandfonline.com/doi/full/10.3402/jom.v6.26102

Wingender, J., Neu, T. R., & Flemming, H. (1999). What are bacterial extracellular polymeric substances? Microbial Extracellular Polymeric Substances, 1-19. https://link.springer.com/chapter/10.1007/978-3-642-60147-7_1

Zaatout, N. (2022). An overview on mastitis-associated Escherichia coli: Pathogenicity, host immunity and the use of alternative therapies. Microbiological Research, 256, 126960. https://www.sciencedirect.com/science/article/pii/S0944501321002676

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