There are plenty of medicinal plants with antibacterial activity. However, it seems that garlic has the most powerful natural antibiotic effect.

Garlic is a plant with many virtues. We use it not only to prepare delicious dishes but also to prevent and treat different diseases and health disorders. Researchers have demonstrated that garlic can be useful in treating and preventing multiple bacterial infections. This is due to the broad-spectrum activity and efficacy of its natural antibiotics against multiple drug-resistant bacteria.

Things you should know about bacteria

Bacteria are simple organisms formed of a single cell. They colonize every corner of our planet and are essential to maintain the equilibrium of its ecosystems.

The number of bacterial cells in our body is much more important than the number of human cells. The majority of bacteria in our bodies are harmless. There are even some species of bacteria that help us keep our bodies healthy and enhance our ability to recover from illnesses. A relatively small number of bacterial species cause disease. We use antibiotics to fight such harmful microorganisms.

What about antibiotics?

An antibiotic or antibacterial is an antimicrobial drug that we use to prevent and treat of bacterial infections. There are two types of antibiotics. There are antibiotics that kill bacteria and other antibiotics that only inhibit their growth.

Antibiotics and vaccination, helped medicine nearly eradicate many diseases throughout the world. However, their effectiveness and easy access have also led to their inappropriate use and the development of resistance. That means that someday we will not find antibiotics capable of treating infections that nowadays we consider common and easy to cure.

This problem is so threatening that the World Health Organization classifies antimicrobial resistance as a serious threat. It can affect anyone of any age and in any country. Natural antimicrobials are the solution to this problem. They are highly effective against bacteria and succeeded in staying effective for thousands of years.

Garlic as a medicinal plant

Dietary factors were believed to develop or treat several diseases since ancient times. People of different civilizations believed in the power of Garlic (Allium sativum) and its ability to promote health. This plant is renowned in various traditions as an excellent medicinal plant, not only for its prophylactic but also for therapeutic benefits.

Garlic is a bulbous plant. It belongs to the family of liliaceae. It is easy to grow even in harsh climates. There are several varieties such as white, purple, or pink garlic.

The virtues of this medicinal plant are mainly due to the bioactive substances present in the bulbs. Allicin is the most important among these substances. It is normally present in an inactive form called alliin. Allinase is the enzyme that transforms alliin into allicin when garlic cloves are ground. We can find allicin essentially in aqueous extracts or homogenates of fresh bulbs.

There are many other types of garlic preparations such as aged garlic extract. It has many medicinal properties. To make this extract you have to put some slices of dried bulbs in 15-20% ethanol for a year and a half. This process modifies garlic composition and causes the loss of a considerable amount of allicin. However, new water-soluble bioactive components with better stability and powerful antibacterial activity appear.

How powerful is the antibacterial activity of garlic?

Among the Allium species, garlic has the best antimicrobial activity against a large number of microorganisms. It showed activity against both gram-positive and gram-negative bacterial pathogens. That means that garlic has broad-spectrum antimicrobial activity.

In fact, researchers have studied the antibacterial activity of garlic against multiple bacterial strains. They found that aqueous garlic extract exhibited antibacterial activity against gram-positive (Bacillus subtilis, Staphylococcus aureus) and gram-negative (Escherichia coli, Klebsiella pneumoniae) strains. The methanol extract was less effective than the aqueous extract. Extracts of hexane, chloroform, and ethyl acetate did not show any antimicrobial activity. The minimum inhibitory concentration of aqueous and methanol extracts against tested bacterial strains was 100-150 µg/ml.

Another study on Escherichia coli, Shigella sp, Salmonella sp, and Proteus mirabilis showed that gram-negative pathogens responsible for diarrhea were highly sensitive to garlic. They even had better sensitivity to garlic than to other synthetic antibiotics.

Researchers have also demonstrated that allicin, one of the active principles of freshly crushed garlic homogenates, has a variety of antimicrobial activities against a wide range of Gram-negative and gram-positive bacteria, including multidrug-resistant enterotoxigenic strains.

Another study showed that aqueous garlic extract exhibited antibacterial effects against 17 multidrug-resistant gram-positive and gram-negative bacterial isolates, including Staphylococcus aureus, Salmonella typhi, Pseudomonas aeruginosa, Escherichia coli, and Proteus spp. The minimum inhibitory concentration (MIC) was in the ranges of 6–11 mg/mL and 7–21 mg/mL, in Gram-positive and Gram-negative organisms respectively.

The study also revealed that the antimicrobial efficacy of aqueous garlic extract is time and temperature-dependent. In fact, the extract maintained its efficacy at room temperature for 7 days. At -20℃ temperature, the activity lasts for 90 days.

I tested it!

I heard a lot about garlic’s antibacterial activity and I was so curious to prove it myself that I decided to run a small test at my school’s microbiology laboratory.

Procedure

I crushed garlic bulbs with a sterilized mortar. I then recovered the extract with filter paper. By adding sterilized water, I was able to obtain 4 solutions with different concentrations: 25%, 50%, 75%, and 100%.

Solutions with different concentrations of garlic extract

To test the antibacterial activity of the different solutions, I prepared a bacterial solution from a strain of salmonella isolated from a fresh sample.

The bacterial solution was used to test the antibacterial activity of the garlic extract and some conventional antibiotic discs for comparison.

I seeded the culture dishes with the bacterial solution, then I added the solutions prepared from the garlic extract in a dish and the antibiotic discs in other dishes. All the dishes were then cultured at 37 ° C (98.6 ° F) for 24 hours.

Results

Bacteria sensitivity test to different garlic extract concentrations

Normally, when a bacterial solution is cultured in a dish, a bacterial layer appears on the surface of the culture medium. However, when we add an antibiotic that is effective on the bacterial strain, it inhibits its growth. This brings up clear discs around the point of application of the antibiotic. We can then deduce the power of this antibiotic against the bacteria cultured by measuring the appearing inhibition diameter.

In our experiment, all tested concentrations of garlic extract showed potent activity against the salmonella strain:

Result of reading the antibiogram (sensitivity test) based on aqueous extract of garlic at different concentrations

The following table shows the diameters of inhibition and the sensitivity of the strain tested to common antibiotics used for this experiment:

Outcome of antibiotic disc sensitivity testing

By comparing the two tables, we can easily deduce that garlic extract has a superior antibacterial activity to most antibiotics tested.

Bacteria sensitivity test to different common antibiotics

In fact, among the 14 molecules used, only Cefatoxime is highly active (42 mm) on the bacterial strain. Moreover, even at low concentrations (25%), the inhibition diameter of the garlic extract (25 mm) remains higher than that of 71.4% of the active molecules tested!

This experiment allowed me to confirm the powerful antibiotic activity of garlic against Salmonella in particular and bacteria in general. Not only that, but its activity is sometimes even more powerful than some synthetic antibiotics commonly used in medicine! This proves that garlic is a powerful antibiotic that can be relied upon to treat bacterial infections.

How does it affect bacteria?

The main antimicrobial effect of allicin is due to its chemical reaction with thiol groups of various enzymes, e.g. alcohol dehydrogenase, thioredoxin reductase, and RNA polymerase, which can affect essential metabolism of cysteine proteinase activity involved in the virulence of some bacterial strains.

What is important is that no tested strains were resistant to garlic, making it a promising antimicrobial agent.

Things to keep in mind

Garlic has a wide spectrum of activity and appears to satisfy all of the criteria for antibacterial agents. It can help us protect food and consumers from the risk of contamination from pathogenic microorganisms.

Due to its broad-spectrum activity and its usage in our daily diet, garlic can be a potent nutraceutical.

Garlic helps you prevent and treat bacterial infections. However, you should always consult your doctor and follow product instructions.

References:

Antimicrobial Spectrum of Allium Species – A Review

A comparative assessment of the antimicrobial effects of Garlic (Allium sativum) and Antibiotics on diarrheagenic organisms

Antimicrobial properties of allicin from garlic

Insecticidal, antimicrobial and antioxidant activities of bulb extracts of Allium sativum

In vitro Antibacterial Activity and Stability of Garlic Extract at Different pH and Temperature