Gut Bacteria Enzyme Can Change Blood Type A Into Much-Needed Type O

gut bacteria enzymes can convert blood types

Story at-a-glance -

  • Although human blood looks the same, it is not identical from one person to another; this fact is an important element in ensuring safety during blood transfusions
  • There are four major blood groups, types A, B, AB and O; type O is considered the universal donor as it does not contain either antigen A or B; type AB is considered the universal receiver as it contains both and can safely accept all blood types
  • A recent study found a gut bacteria enzyme capable of removing the A antigen from red blood cells, effectively making it type O; researchers are moving forward in their search for cost effective and safe ways to use this in a clinical setting
  • Currently, blood donation is the only method to ensure every blood type is available for emergencies; the procedure is safe, effective and may help balance your own iron stores, preventing conditions associated with high iron levels

By Dr. Mercola

While all human blood is red when exposed to air, not all human blood is identical in nature. Every individual has a specific blood group inherited from your parents in much the same way you inherit other characteristics, such as eye color.

Your blood group is determined by the presence or the absence of specific antigens on the surface of every red blood cell. These antigens determine several characteristics in your blood, including blood type, and may be either proteins or complex sugar molecules.1

There are four major blood groups determined by the presence or absence of two antigens, A and B. Additionally, there is an Rh factor that may be present or absent. The combination of the A or B antigen and Rh factor create the eight most common blood types.2

However, there are 600 other known antigens potentially present on the surface of the red blood cell and the presence or absence of these create a "rare blood type" unique to specific ethnic groups.

Blood without either the A or B antigen and without the Rh factor, called blood type O negative, is commonly called the universal donor type and is highly sought after. Researchers have now discovered an enzyme secreted by specific gut bacteria transforms type A blood to type O.3

Blood Typing Necessary for Donation and Transfusion

To fully appreciate the impact this may have on emergency care, it's important to address the challenges of transfusion. In order to be successful, donated blood must match the individual receiving the blood in both blood type and Rh factor, as explained in this short video.

Although blood type distribution may differ in specific ethnic groups, the approximate distribution in the U.S. is:4

Blood type Percent of population


38 percent


7 percent


34 percent


6 percent


9 percent


2 percent


3 percent


1 percent

As you can see, the most common blood type is O-positive followed closely by A-positive. Someone who is A-positive may receive A-positive, O-positive or O-negative blood, but someone who is A-negative may only receive A-negative or O-negative blood.

In other words, blood cells without any antigens — blood type O — may give to type A or type B blood. If the blood is Rh negative it may be used in a transfusion for someone with Rh negative or RH positive, but the reverse is not true.

The antigens on the blood cells are a substance to which the immune system may respond, triggering a severe and immediate attacked by neutrophils. When a patient receives a blood transfusion containing antigens different from their own, the immune system attacks the donor red blood cells in a response that may be lethal.5

By increasing the amount of blood available for transfusion, it reduces the number of potential fatalities when the right blood type is not available. According to the National Blood Data Resource Center, those over 69 receive half of all transfusions of whole and red blood cells given.6 The demand for blood is only increasing as the aging population grows.

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Gut Bacteria May Change Blood Type

The idea of transforming blood type using enzymes is something scientists have been exploring for years. This new research presented at the American Chemical Society national meeting in Boston represents the most promising option discovered thus far.7

In laboratory testing, the enzymes were able to completely convert blood type A to blood type O.8 Enzymes discovered in the past had been able to change type B blood to type O but the process was too expensive and inefficient for real world use.9

Lead author, Stephen Withers, Ph.D., from the University of British Columbia (UBC) remarked scientists have been pursuing the idea of adjusting donated blood for years but have yet to find efficient, selective enzymes that would also be economical and safe. To analyze enzymatic candidates more quickly, Withers and colleagues used metagenomics to study ecology.10

Using this process to cast a wide net allowed the team to sample genes from millions of microorganisms without using individual cultures. They ultimately found successful candidates from bacteria in the human gut microbiome. Withers is now working with colleagues at the Center for Blood Research at the UBC to validate the enzymes and test them on a larger scale. Withers commented:11

"I am optimistic that we have a very interesting candidate to adjust donated blood to a common type. Of course, it will have to go through lots of clinical trials to make sure that it doesn't have any adverse consequences, but it is looking very promising."

How May This Process Benefit Real-World Problems?

Although previous enzymes discovered were able to change type B blood to type O blood, this new process is 30 percent more effective. Dr. Alyssa Ziman, director of transfusion medicine at UCLA Health, believes the challenge is to make the procedure more economical and safe on a unit by unit basis.12

In targeted situations where type O blood is scarce, the ability to transform one type of blood to another could save lives. However, the process would necessarily be limited to how much blood could be effectively transformed and the speed in which it could occur.

Since blood is never pooled — it isn't stored by putting all type A blood together, for example — to decrease the risk of spreading infectious diseases, any altering of blood type would have to be done one donation at a time. This new process becomes another step and another cost, according to Ziman.13

As the number of individuals with O-negative blood is relatively rare, transforming type A blood to type O may be effective, especially in large emergency situations. Withers hopes as the investigation for safety moves forward, the process may also progress to an economical and safe means of transforming blood types.

History of Blood Typing

Prior to 1900, scientists believed all blood was the same. Transfusions had been practiced intermittently since the 1600s but the assumption all blood was of the same type often led to catastrophic transfusions between humans or between animal blood and humans in an attempt to transfer certain qualities.14

For instance, a recipient may receive the blood of a lamb in order to become meek like a lamb. For this reason, France and the U.K. banned the practice for more than 100 years.

In 1900, Dr. Karl Landsteiner from the University of Vienna demonstrated that when blood was mixed between two different people the blood cells sometimes clotted, explaining the tragic results of transfusion between unmatched blood types.15

In 1901 he published information about different types of blood cells and blood groups he had detected, leading to the discovery of safe transfusions between people with compatible blood types. He received the Nobel Prize for medicine in 1930 for his work16 and went on to discover the Rh factor experimenting with the blood of rhesus monkeys.

Blood type testing is done using a blood sample. The sample is mixed with antibodies against type A and type B blood and then checked for clotting.17 If the blood clots, it means it reacted with one of the antibodies. In other words, if your blood sample reacts with type A antibodies, your blood does not have type A antigens.

A second step is then done in which the liquid part of your blood, without cells, is mixed with blood known to be type A or type B. People with type A blood have anti-B antibodies and people with type B blood have anti-A antibodies. Type O blood contains both types of antibodies. Using the results of both tests, the laboratory accurately determines your blood type.18

Research carried out in Heidelberg, Germany, in 1911 demonstrated ABO blood types are inherited and determined by genes on chromosome 9. They're not changed as a result of environmental influences during life, but result from the inheritance from each parent. Both A and B are dominant over type O, so those with type O blood type must have both parents with type O blood type.19

Cell Surface Antigens Serve More Functions

More than the A or B antigen reside on the surface of red blood cells. In fact, there are 36 currently recognized blood group systems. Not all are important in the transfusion of blood from one person to another. An interesting example of this is the Duffy protein, named after a hemophiliac patient.20

The Duffy glycoprotein is a receptor for chemicals secreted by blood cells during inflammation.21 Interestingly, it is also a receptor for Plasmodium vivax (P. vivax), the parasite responsible for the development of malaria.22 In 1950, a patient known as "Mr. Duffy" developed an antibody to what is currently called the Duffy A antigen after receiving a blood transfusion.23

Individuals who are Duffy negative are resistant to P. vivax invasion. The antigen may be a scavenger on the red blood cell surface to eliminate toxins produced in some pathologic situations. While P. vivax triggers nearly 80 million cases of malaria each year in the tropical and subtropical world, it is nearly absent from West Africa, where more than 95 percent of the population is Duffy negative.24

Although not one of the major antigens responsible for triggering a transfusion reaction, the Duffy blood group factor has occasionally caused difficulty in transfusions.25 The antigens have also been found on the surface of Purkinje cells in the brain and cells in the colon, spleen and thyroid gland.26

Donating Blood Is Safe and Saves Lives — Including Your Own

A continuous supply of blood is critical to meet the needs of individuals in your geographical area. Blood is only available through volunteer donors and it is unfortunate that less than 5 percent of eligible people actually donate blood.27

Your body replaces the fluid within 24 hours and red cells within approximately five weeks. Blood donations are sanitary and safe for the donor. Most people feel fine after donating, but it's important to remember to eat and drink plenty of fluids afterward to help your body replace plasma, and to avoid any heavy lifting and strenuous exercise for 12 hours.28

Blood donations benefit the community and your own health. Repeated donations help reduce blood viscosity, and limit damage to the lining of your blood vessels, resulting in fewer arterial blockages.29 For every unit of blood you donate, you lose approximately one-quarter of a gram of iron, which is one of the best ways to avoid health risks associated with iron overload.

Iron is essential to health, as it helps form red blood cells, and is a key component in a variety of proteins and enzymes. However, it is important to have a balance of iron as either excess or low levels can cause health problems. Individuals who have too much iron may suffer from nonalcoholic fatty liver disease, which currently affects up to 25 percent of Americans.

Excess iron also increases your risk of liver damage and liver disease, even in the absence of hemochromatosis. You may have a two to three times greater risk of bowel cancer30 with high iron levels, and other research has linked high iron to Alzheimer's disease31 and cardiac arrhythmias.32

Donating blood twice a year is a simple, safe and effective way to help others and yourself. With each donation you'll get a mini physical to determine your eligibility, and your blood will be tested for 13 different infectious diseases. If something comes back positive, you'll be notified. You'll also lower your iron stores if your levels are higher than ideal. To learn more about this, see "Why Checking Your Iron Level Is so Crucial for Optimal Health."