Resist-Me-Not: Meet Deinococcus radiodurans, the Bacteria Fighting Against Antibiotic Resistance

By: Micah Reiter '23 and Eva Volckova

D. radiodurans is one of the world’s toughest bacteria. It is resistant to incredible amounts of radiation, and it can survive in outer space. It has the potential to be used in radiation cleanup and can even be used as a model for life in space! But, in addition to these extreme environments, D. radiodurans has found a home in another surprising place: our skin. Do we want D. radiodurans on our skin? Could we become radiation-resistant thanks to our cohabitants? Well, not quite.

Figure 1. Deinococcus radiodurans tetrad, where each section is a bacterium, as seen by electron microscopy

D. radiodurans might not turn us into superheroes, but it does have the potential to play a pretty heroic role in the treatment of a terrifying variety of microbes known as antibiotic-resistant bacteria. We have all heard of antibiotics. Maybe you have known someone who contracted strep throat or a urinary tract infection. They probably went through their prescription and came out of it infection free. But with antibiotic-resistant bacteria, the antibiotics we typically use to treat infection can be ineffective. S. aureus is an example of an antibiotic-resistant bacteria that has developed a defense mechanism against many common antibiotic treatments. Unfortunately, infections with S. aureus have a mortality rate of 25%, so it is important we find a way to treat these antibiotic-resistant strains. Scientists speculate that it is S. aureus’s ability to secrete a biofilm that increases its antibiotic resistance. You can see the biofilm secreted by S. aureus covering an agar plate in Figure 2, shown in fluorescent green (but we won’t go into detail about this part of the experiment).

Figure 2. S. aureus biofilms were visualized by confocal laser scanning microscopy

The interactions between D. radiodurans and pathogenic bacteria such as S. aureus are the focus of the study we will tell you about today. D. radiodurans has been found in higher concentrations on the skin of healthy individuals than on those with S. aureus infections. Scientists began to wonder why—could D. radiodurans potentially have an effect on S. aureus populations? This is the question Chen et al. (2021) sought to answer: they wanted to know if D. radiodurans, the hearty bacteria that has been the star of many popular science articles, could disrupt biofilm formation of S. aureus and make it more susceptible to treatment.

And the answer was yes! This is highlighted in their first experiment, which shows that biofilm formation is decreased in the presence of D. radiodurans. Of course, the next logical question was: how does D. radiodurans disrupt the biofilm? After looking at various different cell components, they determined that the exopolysaccharides secreted from D. radiodurans are responsible for its incredible bacteria-busting effects. But how does the exopolysaccharide disrupt the bacterial biofilm? Well, it turns out that the D. radiodurans exopolysaccharides don’t actually kill S.aureus. Instead, they prevent the communication between S. aureus cells that is necessary for the biofilm to grow. And how do they do that? Well, that question is getting beyond the scope of this study, but you can learn more here.

Once the researchers determined that D. radiodurans is able to inhibit the formation of biofilms, they started looking into the implications of this breakthrough on human health. Seeing the effects play out in a controlled environment such as a petri dish is impressive, but there is still a long way to go between discovering these exciting properties and applying them to a person. One important step in this process is determining if D. radiodurans is able to break up biofilms of harmful bacteria in live cells. The researchers tackled this new question using mice. (The animals were numbed for the following procedure.)

For the control, the mice were burned on the back of their necks and S. aureus was applied to the wound. This burn disrupted the natural barriers of the skin and allowed the infection of S. aureus to take hold. The two experimental groups had Deinococcus radiodurans exopolysaccharide (called DeinPol from here on out) added in different concentrations in addition to S. aureus. In Figure 3A, you can see that there are more colony forming units (CFU, which is an estimate of the number of viable bacteria) of S. aureus in the control (bar 1) than in the experimental groups with our favorite bacterial exopolysaccharide applied (bars 2 and 3).

This result can actually be seen in the tissue samples of infected mice shown in Figure 3B. Notice the 3rd and 4th columns in the grid. On top is a big picture image (40x magnification), and on the bottom is a close up view (400x magnification) of the same sample. In column 3, where only S. aureus was added, you can see large, dark purple splotches on the surface of the tissue sample. This is S. aureus, a Gram positive bacteria. Now, look at column 4, where DeinPol was added along with S. aureus. You can see that there is noticeably less dark purple in this tissue sample, showing that there is less S. aureus growth. Figure 3B allows you to visualize the difference that D. radiodurans can make in preventing population growth.

Figure 3. A) The effect of S. aureus in combination with DeinoPol treatments on colony forming units. B) Mouse tissue sections after various treatments, imaged by a microscope after Gram-staining.

Showing the effectiveness of D. radiodurans in living tissues is one step in the right direction. Another big consideration for this incredible microbe is its ability to play well with others. Essentially, researchers wanted to know how D. radiodurans would interact with antibiotics. Chen et al. looked at how D. radiodurans worked against biofilms when combined with four different antibiotics: penicillin, vancomycin, oxacillin, and cefazolin.

Figure 4A-D all have the same experimental design, but use different antibiotics. You can look at the entire figure at the end of the article, but we will only look at two parts of it. Let’s focus on Figure 4A for now, penicillin (Peni).

Figure 4A. S. aureus was grown on plates with DeinoPol (10µg/ml) for 24 hours, then incubated for 6 hours in the presence or absence of penicillin (Peni) (3, 10, or 30µg/ml)

Bar 1 has no Peni and no DeinoPol, showing how S. aureus would grow with no intervention. Bar 2 shows the effects of only DeinoPol, which reduces the biofilm.

Now we get into the really interesting combinations. If you look at bar 3, you will see that there is a bracket at the top connecting it to bar 6. What this means is that bar 3 is the control: it has Peni at a concentration of 3 µg/mL without DeinoPol. This makes bar 6 the experimental group: it has 3 µg/mL Peni and DeinoPol. The single star at the top of the bracket means that there is a significant difference between the two groups. In other words, adding DeinoPol to Peni makes a treatment that is more effective at inhibiting the biofilm. Plus, if you compare bar 6 (DeinoPol+Peni) to bar 2 (DeinoPol only) you can see that the combo is also more effective than DeinoPol alone.

Why does this matter? To simplify, combining antibiotics with DeinoPol (remember, this means the exopolysaccharides from D. radiodurans) shows a promising ability to decrease the biofilm of S. aureus, an antibiotic-resistant bacteria. DeinoPol+Peni is better than Peni alone—this confirms that adding our bacteria to typical antibiotics might make treatments more effective!

Figuring out exactly what antibiotic/D. radiodurans cocktail works the best is going to be a big process. Chen et al. started working through this by testing each antibiotic at three concentrations: 3 µg/mL, 10 µg/mL, and 30 µg/mL. Let’s look at Figure 4C, which is testing the antibiotic oxacillin (OXA).

Figure 4C. S. aureus was grown on plates with DeinoPol (10 µg/ml) for 24 hours, then incubated for 6 hours in the presence or absence of oxacillin (OXA) (3,10, or 30 µg/ml)

There are only two concentrations that make a significant difference in the ability of the antibiotic to inhibit the biofilm. It seems that 3 µg/mL of oxacillin isn’t significantly improved by the presence of D. radiodurans (there is no bracket connecting them). However, at 10 µg/mL and 30 µg/mL of oxacillin, our friendly bacteria is able to improve the treatment.

The research of Chen et al. has big implications for human health. As we mentioned earlier, it can be difficult to treat MRSA or other bacterial infections as a result of antibiotic resistance. By adding D. radiodurans to a traditional antibiotic, we may be able to stop antibiotic resistance and make treatments more effective. However, while the research is promising, ensuring that this incredible microbe is safe for human use will be a long process. And, as seen in Figure 4C, there is still considerable work to be done to determine which combinations and concentrations of D. radiodurans and antibiotics are effective. Still, we have hope that in the coming years this incredible microbe might make its way into clinical settings and help save lives of people infected by antibiotic resistant microbes like S. aureus.


Figure 4A-D. S. aureus was grown on plates with DeinoPol (10 µg/ml) for 24 hours, then incubated for 6 hours in the presence or absence of (A) penicillin, (B) vancomycin, (C) oxacillin, or (D) cefazolin. Biofilms were determined by crystal violet assay.


About the Authors: 

Eva and Micah, lab partners and blog partners!

Left: Micah, class of 2023, is a Biological Science and Religion double major pursuing a career as a Nurse Practitioner. They have worked as a nursing assistant and can tell you first hand what various pathogenic microbes can do to a person…and what they smell like (hint: bad). Micah’s favorite smelling microbes, on the other hand, are Streptomyces species, which help give soil its distinctive petrichor smell after it rains.

Right: Eva, class of 2022, is a Biological Sciences major and Chemistry minor hoping to go into cancer research. In their free time, they love spending time outdoors hiking and birdwatching. They prefer non-pathogenic microbes that are either purple or yellow.


Works Cited:

Chen, Fengjia, et al. “Deinococcus Radiodurans Exopolysaccharide Inhibits Staphylococcus Aureus Biofilm Formation.” Frontiers in Microbiology, vol. 12, 2021, https://doi.org/10.3389/fmicb.2021.712086.

Lewis, Kim. “Persister Cells.” Annual Review of Microbiology, vol. 64, no. 1, 2010, pp. 357–372., https://doi.org/10.1146/annurev.micro.112408.134306.

Singh, R., et al. “Penetration of Antibiotics through Staphylococcus Aureus and Staphylococcus Epidermidis Biofilms.” Journal of Antimicrobial Chemotherapy, vol. 65, no. 9, 2010, pp. 1955–1958., https://doi.org/10.1093/jac/dkq257 .

Singh, Rachna, et al. “Role of Persisters and Small-Colony Variants in Antibiotic Resistance of Planktonic and Biofilm-Associated Staphylococcus Aureus: An in Vitro Study.” Journal of Medical Microbiology, vol. 58, no. 8, 2009, pp. 1067–1073., https://doi.org/10.1099/jmm.0.009720-0 .

Slade, Dea, and Miroslav Radman. “Oxidative Stress Resistance in Deinococcus Radiodurans.” Microbiology and Molecular Biology Reviews, vol. 75, no. 1, 2011, pp. 133–191., https://doi.org/10.1128/mmbr.00015-10 .

Wenzel, Richard. “The Impact of Hospital-Acquired Bloodstream Infections.” Emerging Infectious Diseases, vol. 7, no. 2, 2001, pp. 174–177., https://doi.org/10.3201/eid0702.010203.