|Microscopy image of Enterococcus. <SOURCE>|
Biofilms have five phases of development, as you can see in the figure below. The bacteria attach to the surface (phases 1 and 2) and proceed to multiply, thereby contributing to growth of the biofilm (phases 3 and 4). Once the biofilm has grown and matured, some of the biofilm bacteria are released to travel to new substrates and establish new biofilm infections (phase 5). Often this dispersal is mediated by quorum sensing molecules, which are molecules used by bacteria to sense the presence of other bacteria, as well as the population size of the bacterial community. Put plainly, a single bacteria knows there are a lot of other bacteria present in the community when the quorum sensing molecule concentration is high in the environment.
|Five stages of biofilm development: (1) Initial attachment,|
(2) Irreversible attachment, (3) Maturation I,
(4) Maturation II, and (5) Dispersion. <SOURCE>
The study focused on Enterococci, which are gut commensals (meaning they harmlessly live with you all the time) as well as very serious potential-pathogens that can cause very severe biofilm infections. The research group showed these bacteria do in fact produce, and are sensitive to, the AI-2 quorum sensing molecule. The presence of AI-2 on an Enterococcus biofilm indeed caused disruption of the biofilm, which affects phase 5 of the biofilm formation as discussed above. Interestingly, the group used both RNA-sequencing and molecular techniques to show that this Enterococcus biofilm dispersion was mediated by prophages that were integrated into the bacterial genomes, and that this dispersion could not occur without the prophages. This is really important because it provides us with further insight into how these pathogenic bacteria infect humans, and because it further illustrates the crucial roles phages have in bacterial virulence.
|Bacteriophages, like this one infecting a bacterial cell, can|
transfer virulence genes and make the bacterial host
This paper is super interesting because it really highlights the roles for bacteriophages in bacterial pathogenesis, virulence, and infection. These findings are particularly important to the microbiome field where we are very interested in the medical benefits of probiotics, prebiotics, and fecal microbiome transplants. One question that came to mind while reading this study was how commensal phages might be impacting administered probiotics? Additionally, what kind of phage screening might we see in the future as we use more and more fecal microbiome transplants? I am not saying that these therapies are dangerous because of bacteriophages, but I want to highlight these important questions and the fact that phages certainly play complex roles in bacterial pathogenicity and our health. Of course, further research is going to be needed to tease this apart further, so we will have to stay tuned.
For the whole story, feel free to check out the paper. It is open access, which means anybody can access and read it. It is actually a pretty straightforward read so definitely check it out. Additionally, always feel free to drop me a comment below with any questions, comments, or opinions about the topic I covered above.
Rossmann, F., Racek, T., Wobser, D., Puchalka, J., Rabener, E., Reiger, M., Hendrickx, A., Diederich, A., Jung, K., Klein, C., & Huebner, J. (2015). Phage-mediated Dispersal of Biofilm and Distribution of Bacterial Virulence Genes Is Induced by Quorum Sensing PLOS Pathogens, 11 (2) DOI: 10.1371/journal.ppat.1004653