Science Diction Podcast | Bacteriophages

Transcript – Bacteriophages: A Possible Alternative or Supplement to Antibiotics

Dr. Amy Manning-Boğ
Welcome to season two of Science Diction from MRIGlobal. We’re so excited to be back in 2024 and really appreciate you listening to our first season.

Imagine that you are host to the deadliest viruses on the planet. Your body is theirs. They colonize your hands, the inside of your mouth, lungs, and even your gut. And without so much as a sneeze or cough, you’re transmitting these viruses to everyone around you. But you don’t have to imagine, because it’s true.

My colleague Kristen Bates is a researcher specializing in infectious disease and biothreat detection. In addition to specialties and high containment laboratory work and select agents, she also has experience in food, microbiology, and a passion for bacteria.

Today on the show – bacteriophages – how they are such effective killers of bacteria, their role in disease diagnostics, and how they might one day serve as an alternative or supplement to antibiotics. I’m Amy Manning- Boğ and this is Science Diction from MRIGlobal.

Kristin Bates
Bacteriophages or phages for short, are viruses that infect and replicate within bacteria. So a little etymology there. The word bacteriophage comes from the Greek words of bacterium, meaning small staff and phage in meaning to eat. These viruses are the natural predators of bacteria, and they’re the most numerous viruses in the world.

Dr. Amy Manning-Boğ
So what comprises the bacteriophage?

Kristin Bates
So bacteriophage is just a really simple structure. They have their genetic material, either DNA or RNA, which is encased in a protein coat, and then they have a tail. There are two different types. There are lysogenic bacteriophage and lytic bacteriophage. The lysogenic ones integrate their genetic material into the bacterial genome and become a prophage. The bacterium continues to replicate normally, and the viral genes are passed on to daughter cells during cell division. And that is how the virus just continues to replicate within the bacteria without destroying the bacterial cell.

In a lytic bacteriophage, the phage will attach to the bacterial cell through a viral protein on the phage surface to receptors on the bacterial cell surface. The phage then will inject its genetic material, but it takes over all of the bacterial machinery and it will just replicate itself and create new viral particles until eventually causing the cell to lyse, which is just destroying the cell. It will break apart and release all of the viral progeny out into the environment to then kind of continue that cycle.

Dr. Amy Manning-Boğ
So these sound really simple, really small. How were they first discovered?

Kristin Bates
So it’s very interesting the history of them. So it’s generally accepted that bacteriophages were discovered simultaneously by two researchers. We have Frederick Twort and Félix d’Herelle. In 1915, Twort wrote about all of his observations about what he called a factor that killed bacterial cultures. Twort did not have the funding to look further into his discovery.

And it was d’Herelle that came up two years later in 1917 with his own individual discovery of bacteriophage. He published his research into a monograph that he and he called “The Bacteriophage and its Behaviour” and it reads like a lab manual. You have all of his techniques for isolation, purification, titration.

But it did spark a great deal of controversy. First and foremost, d’Herelle had no formal education. This lack of education meant he did not have a stable position at any institute and did not have a lab or financing until later in his life. His discovery met opposition from immunologists, most notably Jules Bordet who refused to believe that bacteriophage were independent viruses, and he tried to instead fit d’Herelle’s data into his own interpretation based on the interaction between antibodies and the complement system being able to lyse bacterial cells.

Dr. Amy Manning-Boğ
So we had mentioned about the fact that bacteriophages kill bacteria. How is this done?

Kristin Bates
So lytic bacteriophage and that lytic cycle is what actually kills the bacteria. The phage will just commandeer the protein and nucleic acid synthesis machinery to replicate those phage components, making more viral particles in the cell. Eventually, that host’s bacterial cell will burst, which is lysis, and then release all those new phage particles.

Dr. Amy Manning-Boğ
Got it. Lytic. So, I’m curious what first interested you in bacteria and more specifically bacteriophages.

Kristin Bates
So I have a background in food microbiology. The majority of my undergrad was at Iowa State University, where I worked in the meats lab on campus. So I was around around a lot of the food safety aspects. And I know that the dairy industry works hard to ensure a safe, quality milk supply, but biofilm formation is a persistent issue. And that can really add to antimicrobial resistance, as you have these really hardy biofilms on equipment that can then be transferred to cows and make cows sick, which of course we don’t want. So, kind of looking into that and reading about it, I was reading that there are some researchers looking into developing products that you can spray on surfaces that include bacteriophage that will prevent biofilms from forming in the first place.

Dr. Amy Manning-Boğ
That’s fascinating. So, beyond the use of bacteriophages in preventing the formation of biofilm, what are some other applications of this tool in the animal health industry?

Kristin Bates
So, another direction that I stumbled upon and kind of went further into researching is the ability to engineer a bacteriophage, to be a reporter, and you can use it in diagnostics. So rather than just trying to prevent or treat bacterial infections, they can be used to identify them in the first place.

Dr. Amy Manning-Boğ
What are some of the advantages of using bacteriophages in this regard?

Kristin Bates
So the best diagnostic is definitely what is going to be simplest and most cost effective to run. And the good thing about bacteriophages is they are very simple. They are very specific. They target bacteria down to the species or even just the strain level. They are self-replicating. So that will allow for a signal amplification with very minimal preparation or work on a technical level.

Bacteriophages are also unique as they only detect viable cells. That’s a difference between bacteriophage detection methods and things like PCR, where it will detect any DNA or RNA related to the bacteria in question. But that doesn’t necessarily mean that that was alive bacteria. So you don’t know if that’s actually an active infection or if it’s something that in the past that has already been cleared out. So then you’re identifying the wrong thing.

Bacteriophages can also be produced in really high quantities at a pretty minimal cost. And a lot of studies have gone into the stability of them and they do have a very long shelf life and the ability to be freeze dried. So that would just make it a powdered form, which also is very useful kind of for on site, on field usage.

They also generally have a really rapid readout and that can vary depending on how the phage is produced. But generally, it can be within like 1 to 4 hours. There are some studies that manage to get a readout within 10 to 30 minutes, which is really great for a diagnostic.

Dr. Amy Manning-Boğ
That’s an incredible time to result. So, you’ve mentioned diagnostic possibilities in animal agriculture. What about therapeutic ones?

Kristin Bates
Yeah. So bacteriophages have been explored and used in veterinary medicine to treat bacterial infections in animals. This goes back to what we just discussed. Bacteriophages can infect and replicate within bacteria leading to their destruction. This property makes them potential candidates for targeted antibacterial therapy. In veterinary medicine, bacteriophages have been investigated as an alternative or complementary treatment to antibiotics.

The critical factor here is to use bacteriophages that specifically target and kill pathogenic bacteria without affecting beneficial bacteria or causing resistance issues. Research and experimental use of bacteriophages in animals have shown promising results in some cases. Bacteriophage therapy has been studied in various animal species, not just livestock, but also aquaculture and even in house pets.

Dr. Amy Manning-Boğ
So this is really exciting because it seems like this helps address the issues of bacterial antibiotic resistance.

Kristin Bates
Yes, but it’s not all blue skies. While bacteriophage therapy holds potential, there are challenges and considerations. We need to carefully match the bacteriophage to the specific bacterial strain causing infection and further, like antibiotics, there is the possibility of the development of bacteria that are resistant. There are also potential issues of immune response.

Dr. Amy Manning-Boğ
The immune response. Let me pull that thread a bit. Activation of the animal immune system in response. Do you mean like cytokine release syndrome from immune activation?

Kristin Bates
No, bacteriophage is generally considered to have a narrow host range and are specific to bacterial targets only. They do not naturally infect animal cells and their replication is restricted to bacterial hosts. So direct induction of cytokine release by bacteriophages in animals is unlikely. That said, if bacteriophage therapy is used to treat bacterial infections in animals, the release of bacterial components and endotoxin as a result of bacterial lysis by the phages could potentially trigger an inflammatory response. But this response would be a reaction to the bacterial components being released rather than the phages themselves.

Dr. Amy Manning-Boğ
Thinking about antibiotic resistance, can bacteria develop resistance mechanisms to bacteriophages?

Kristin Bates
Yes. That’s also a possibility that the targeted bacteria can develop resistance to the bacteriophage itself. This is also another reason why phage cocktails are recommended. If you only use one phage and there is at least one bacteria with resistance that hangs on, it can then proliferate and the new bacterial population growing from that cell will all have resistance.

Using multiple phages increases the chances of elimination of the bacterial population, even if there are a small number resistant to one of the phages used. The other phage in the cocktail will take care of it instead. Another option is also to combine the usage of bacteriophages with the usage of antibiotics. Research has shown that when a bacteria develops resistance to a bacteriophage, it tends to shed its resistance to antibiotics.

Through this mechanism, bacteria are then susceptible to antibiotics. This makes combination therapy with bacteriophage and antibiotics a great option.

Dr. Amy Manning-Boğ
The role of bacteriophages in diagnostics and potential therapeutics for animal health, while critical, scratches the surface of bacteriophage usage. Indeed, these applications can readily translate to the realm of human health.

Kristin Bates
Bacteriophages can be used as diagnostic tools for human diseases in certain contexts. You may have heard of phage display technology.

Dr. Amy Manning-Boğ
Yes, I have. But please tell us more.

Kristin Bates
Phage display involves expressing foreign peptides or proteins on the surface of bacteriophages. These displayed peptides or proteins can then be used to bind specific targets for diagnostic purposes. Displaying antigens or epitopes on phages can be used to detect the presence of specific antibodies and patient serum samples obtained from blood. In the past ten years, technology has been developed to use bacteriophages, engineered to act as biosensors by displaying protein that gives off a signal which it specifically binds to a target molecule.

These phage-based biosensors can be used for rapid and highly specific detection of disease markers or pathogens, enhancing the accuracy of diagnosis and could improve the speed of diagnosis as well, leading to an improved clinical outcome. Research shows that diagnostic assays using this technology outperform conventional culture based and molecular detection methods.

Dr. Amy Manning-Boğ
So, Kristin, we talked about diagnostic and therapeutic bacteriophages in animal health and for diagnostics for human health. What about bacteriophages for therapeutics for humans?

Kristin Bates
Phage therapy has been explored for various bacterial infections, and I think I know where you’re going with this, including those caused by antibiotic resistant bacteria, research and clinical trials have investigated the use of phage therapy in wound infections, respiratory infections, urinary tract infections, as well as others, but…

Dr. Amy Manning-Boğ
Caveats exist.

Kristin Bates
Yes. For therapeutics for animals, the specificity of the bacteriophages for the correct strains, the immune response, the impact of endotoxin from lysed bacteria in the bloodstream, development of a neutralizing antibody. As with any potential human therapeutic, the full gamut of non-clinical and clinical trial testing for safety and efficacy must be evaluated.

Dr. Amy Manning-Boğ
So, Kristin, if we’ve known about phages for a hundred years, what made them fall out of favor?

Kristin Bates
In the 1940s, there are a number of phage products developed for human use in the U.S. that were marketed for a wide range of bacterial infections, but they did not work particularly well, and it is suspected that this is due to improper purification and storage at the time, as it wasn’t well understood, as well as we didn’t have as much knowledge of just how selective the bacteriophages were at the time. So they weren’t sure which ones were actually be useful against the specific bacterial infections. Once antibiotics hit the market as well, then we didn’t really have a need to continue research into phage therapy specifically.

There is also a political component that this was during the time of World War II. So Western countries, including the U.S., had a lot of access to antibiotics, whereas antibiotics were not as easily accessed in the east, namely Russia, Poland and the Republic of Georgia at the time. So those countries continued research into phage therapy, and that is where a lot of background research actually still is.

Dr. Amy Manning-Boğ
So what do you find most exciting about the use of phages?

Kristin Bates
What excites me most about bacteriophages is the idea that antibiotics have been a really useful tool. But we talked about that caveat that bacteria develop resistance to antibiotics. Bacteriophages, on the other hand, can co-evolve as bacteria develop their resistance mechanisms. Phages have to do this just to survive, as they can only replicate in a bacterial host. So if you think about it, Amy bacteriophages in a way, are nature’s antibiotic, and we’re just capitalizing on it.