How do Bacteria Keep People Healthy?

Bacteria are living things made up of just one cell, but they come in all kinds of shapes and sizes. Bacteria are so tiny that they cannot be seen without a microscope, but they can be very different from each other, allowing them to live in lots of different places and perform many jobs. Bacteria are everywhere, from deep in the ocean to active volcanoes, in the air, and on every plant and animal on the planet—even people! Even though you cannot see them with your eyes, bacteria are responsible for supporting life on Earth. They can break down nutrients in the soil to help plants grow, and they help you digest the food in your gut [1].

Bacteria often get a bad reputation, as some species (specific types of bacteria) can make people sick—which is why it is important to always wash your hands! But there are many other species that actually help you to stay healthy. Many bacteria and other microbes live in and on your body, and they can protect you from harmful bacteria (called pathogens) and help your immune system. In your intestines, you have many types of bacteria all working together and performing important jobs. Intestinal bacteria help you digest the food you eat, produce essential vitamins, and fight against harmful bacteria or microbes you accidentally ingest (Figure 1). In fact, the human gut hosts approximately 100 trillion microbes, which play a vital role in human health [2]. This bacterial community is important not just for your physical health [3]—some studies have even shown that the bacteria in and on your body can affect your mental health, too [4]. Now that you know how bacteria work in your body to keep you healthy, let us look at how scientists are trying to change the job of bacteria to help fight diseases!

How do we use Bacteria to Treat Disease?

Scientists can take two main approaches if they want to use bacteria to treat diseases. The first is to use bacteria that exist in the environment naturally, either on their own or working together in groups. The second is to engineer bacteria in a laboratory to carry out a specific task. Many foods contain natural bacteria that help to keep people healthy—for example, the bacteria in natural yogurt break down food in the gut, which helps the body to access the nutrients it needs to grow. These natural bacteria can also be taken as a tablet, called a probiotic, to make sure people get enough of the helpful bacteria. Probiotics are currently being tested in humans, to help researchers discover new ways of helping patients [5].

Every cell in the body has a job, whether it is making the hair on your head or forming the muscle in your heart, so every cell contains a set of instructions called DNA that tell the cell what to do. Researchers can edit the DNA of bacteria to give them new instructions, so they can perform specific tasks for people, and this is called genetic engineering. For example, if your body does not produce enough of a protein it needs, we can take the gene (a section of DNA that performs a specific function) that produces that human protein and add it to the DNA of bacteria. Once the bacteria have the new instructions, they will produce the lacking protein, and we can use those bacteria to make a medicine that you can take when your body needs it. In this way, we can work with bacteria so that they can make the medicine people need [6]. This allows scientists to correct errors in people’s bodies and prevent patients from getting sick.

To design engineered bacteria to combat disease, there are many questions that we need to consider. Firstly, depending on the disease we want to treat, we can use different species of bacteria. For example, if we want to treat a disease in the gut, we could use bacteria that already live inside the intestines.

Some commonly used species are Escherichia coli Nissle 1917 [7], which was discovered in the gut of a First World War soldier, and Lactobacillus bacteria, which are often found in the yogurt at your local supermarket. Once the right bacteria for the job are chosen, we need to engineer their DNA to produce the medicine or drug we want, and then check that everything is working as expected (Figure 2).

Why Use Bacteria When We have Medicine Already?

Normally, when you are sick, you might take medicine to make you feel better or to fight the disease. Unfortunately, there are diseases that do not yet have medicines that can treat them, and many current treatments can cause unpleasant side effects. For example, the medicines used to kill harmful bacteria often kill the helpful bacteria at the same time and then those helpful bacteria cannot do their jobs. Instead of using medicine made from plants or chemicals, scientists can change the DNA of bacteria so that they can produce the medicine for us. Let us take diabetes as an example. Diabetes occurs in people who cannot make the chemical insulin, which regulates blood sugar, and so they need to take insulin as a drug. In the past, insulin from cattle and pigs was used to treat diabetes in humans, but it caused allergic reactions in many patients [8]. Scientists have since engineered bacteria to include the gene for making human insulin. Today, these bacteria are grown in large containers where they make insulin, which can be collected and used for diabetes treatment, instead of taking it from animals!

Using bacteria in this way offers many advantages over traditional drugs: bacteria are cheaper, grow quickly, and can make lots of the medicines we need. Scientists are even working on making engineered bacteria in a pill form—where the helpful bacteria go into your body and make the medicine right where it is needed. In the future, doctors might give patients special bacteria to treat diseases, so we will not always need to rely on regular drugs or chemicals to feel better.

Looking Forward

Scientists have now engineered many bacteria to treat human diseases, but none of these engineered bacteria have been approved for use in humans yet. This is because they are still new therapies and need to be tested in properly designed experiments in humans called clinical trials, to prove they are safe and effective for patients to use. If helpful bacteria escape into nature, they might spread in ways that we cannot control and cause problems. Also, if they grow too much in patient’s bodies, they might make people sick instead of helping them. That is why scientists are careful when using bacteria as medicine. How can we make sure that engineered bacteria only go where we want them to? How can we make sure patients feel comfortable taking these new treatments? If they pass clinical trials, would you feel safe about using engineered bacteria to help treat disease?

While there are still many questions left to be answered, engineering bacteria to help treat disease is an amazing technology that has the potential to transform how patients are treated in the future. Without the bad side effects of some of the medicines used now, and with increased creation of medicines that only go where they need to go in the body, people could get better a lot faster—and that leaves more time for the fun things in life!

Glossary

Species: ↑ A group of similar organisms that can exchange DNA.

Pathogen: ↑ Harmful microorganisms, like bacteria, that can cause disease.

Probiotic: ↑ Beneficial bacteria or other microorganisms that help keep your body healthy, especially your digestive system.

DNA: ↑ Genetic material that contains instructions for how living things look and function.

Genetic Engineering: ↑ A way scientists change an organism’s DNA to give it new traits or abilities.

Gene: ↑ A section of DNA that controls a specific trait, which is inherited from your parents.

Clinical Trials: ↑ Carefully designed scientific studies that test whether new medicines or treatments are safe and effective in people.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

JR was supported by an EPSRC grant (EP/W004674/1). CC was supported was supported by the Biotechnology and Biological Sciences Research Council [grant number BB/T008709/1]. KO was supported through an EPSRC253 studentship (2505625). CB and LD were supported through the European Research Council (ERC) under 254 the European Union’s Horizon 2020 research and innovation programme (grant no. 770835). CB was also supported by the Wellcome Trust (grant no. 209409/Z/17/Z).

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