A Functional Medicine Perspective

Author: Victoria Tyler

If you’ve been dealing with bloating, irregular bowel movements, diarrhoea, or ongoing gut symptoms, you may wonder whether you’ve picked up some form of “bad bacteria” — such as Salmonella or E. coli.

So how do you get rid of it? In this guide we will discuss the different types of bacteria that you can pick up and how you can naturally kill bad bacteria in the gut.

What Naturally Kills Bad Bacteria in the Gut? (Quick Answer)

There are many natural supplements that can reduce harmful bacteria include:

• Garlic (allicin)
• Oregano oil
• Berberine
• Uva Ursi
• Herbal compounds such as clove and thyme

However, these do not selectively kill only harmful bacteria, and overuse can disrupt the balance of the gut microbiome and of your good bacteria.

What Is “Bad Bacteria” Called?

Firstly, it’s important to understand that there isn’t one single type of “bad bacteria.”

In clinical practice, we tend to group them into:

• Pathogenic bacteria
• Opportunistic bacteria
• Dysbiosis (imbalance)

Pathogenic Bacteria

Pathogenic bacteria are those known to cause infection and disease.

Examples include certain strains of Escherichia coli, Salmonella, and Campylobacter.

These bacteria are not usually present in high amounts in a healthy gut and can lead to acute symptoms such as diarrhoea and inflammation.

In clinic, patients can often trace the onset of symptoms to:

• Food poisoning
• Travel
• A stomach bug

These types of bacteria are often self-limiting meaning that you do not normally need to treat them.

Common Pathogenic Bacteria

E. coli (pathogenic strains)
While many strains are harmless, some can cause infection. Symptoms typically begin within a few days and may include diarrhoea, abdominal pain, and nausea.

Salmonella
Often linked to undercooked poultry or eggs. Symptoms usually develop within 6–48 hours and include diarrhoea, fever, and abdominal cramps.

Campylobacter
One of the most common causes of food poisoning in the UK. It is also a well-known trigger for post-infectious IBS.

Shigella
A highly infectious bacterium that spreads easily through contaminated food or water.

Yersinia enterocolitica
Can cause abdominal pain and diarrhoea and, in some cases, longer-term complications such as joint pain.

Vibrio species
Typically linked to contaminated seafood and can cause diarrhoea, cramps, and dehydration.

Opportunistic Bacteria

Opportunistic bacteria are more commonly what we see in practice.

These bacteria are normally present in small amounts but can become problematic when they overgrow.

Examples include:

• Klebsiella
• Streptococcus
• Enterococcus

These may increase after:

• Antibiotic use
• Chronic stress
• Low stomach acid

When they overgrow, they can contribute to symptoms such as bloating, gas, and fermentation.

Dysbiosis

In most cases, gut symptoms are not caused by a single pathogen, but by:

Dysbiosis — an imbalance in the gut microbiome

This involves:

• Too many opportunistic bacteria
• Too few beneficial bacteria such as Lactobacillus
• Reduced microbial diversity

Symptoms of Gut Bacteria Imbalance

Common symptoms include:

• Persistent bloating (especially after eating)
• Gas and belching
• Constipation or diarrhoea
• Brain fog and fatigue
• Food intolerances
• Skin issues such as acne or eczema

What Naturally Kills Bad Bacteria in the Gut?

Clinically, I am seeing more patients trying to “kill bad bacteria” using supplements such as oregano oil, berberine, and garlic.

While these can be effective when used correctly, some patients experience worsening symptom, increased sensitivity to foods, recurring gut issues.

The reason is that the gut is not something you can simply “clean out.”
It is a complex ecosystem, and if approached incorrectly, it can become further imbalanced.

Garlic (Allicin)

Garlic contains allicin, a potent antimicrobial compound that acts against bacteria, fungi (including Candida), and parasites.

It is commonly used in SIBO protocols, although it may not be well tolerated in IBS patients.

Oregano Oil

Oregano oil contains carvacrol and thymol, which have strong antimicrobial properties.

It is also often used in SIBO protocols but acts as a broad-spectrum antimicrobial, meaning it can also affect beneficial bacteria.

Berberine

Berberine has antimicrobial, anti-inflammatory, and metabolic benefits.

It is widely used in protocols for SIBO, Candida, and dysbiosis, although some patients may experience digestive side effects.

Green Tea and Polyphenols

Polyphenols offer a gentler approach.

They help to:

• inhibit harmful bacteria
• support beneficial bacteria
• reduce inflammation

Herbal Combinations

In some cases, combinations of herbs such as oregano, berberine, neem, clove, and cinnamon are used in structured protocols.

Does Killing Bad Bacteria Actually Work?

While antimicrobials can reduce bacterial overgrowth in the short term, they often do not address the underlying cause.

Many patients experience temporary improvement, followed by relapse. This is because

herbal supplements reduce both harmful and beneficial bacteria, which can lower microbial diversity.

This is important because a diverse microbiome is strongly linked to gut health and resilience. When diversity is reduced, it can create space for opportunistic bacteria or yeast to overgrow.

Bacteria Can develop resistance

Microbes can become more resistant over time, especially with repeated use of antimicrobials.

When antimicrobials are used frequently, they eliminate weaker bacteria first, allowing more resistant strains to dominate. This can contribute to a more imbalanced microbiome and recurring symptoms.

Biofilms Protect Bacteria

Some bacteria form protective layers known as biofilms, making them harder to eliminate completely.

Biofilms allow bacteria to attach to the gut lining and shield themselves from both antimicrobials and the immune system. As a result, bacteria can survive treatment and re-emerge later.

The Root Cause Has Not Been Addressed

While antimicrobial treatments may reduce bacterial overgrowth in the short term, they do not address why the imbalance developed in the first place. If the underlying drivers are not identified and corrected, symptoms are likely to return.

Common underlying causes include:

• Poor diet
  Diets high in sugar and ultra-processed foods can feed opportunistic bacteria and contribute to imbalance.
• Low stomach acid
  Stomach acid plays a key role in controlling bacterial levels. When it is low, bacteria are more likely to survive and colonise the small intestine.
• Poor gut motility (MMC dysfunction)
  The migrating motor complex helps to clear bacteria from the small intestine between meals. When this is impaired, bacteria can accumulate and overgrow.
• Chronic stress
  Stress can affect digestion, motility, and the gut–brain axis, creating an environment where imbalance is more likely.
• Previous infections
  Food poisoning or gut infections can disrupt the microbiome and, in some cases, trigger longer-term issues such as post-infectious IBS or SIBO.
• Long-term use of antibiotics or PPILong-term use of antibiotics or PPIs
  These can significantly alter the gut environment, reducing beneficial bacteria and increasing the risk of imbalance.

Addressing these underlying factors is key to achieving lasting improvement, rather than temporary relief.

Do You Actually Need to Kill Bad Bacteria?

Many patients improve significantly without antimicrobial treatment.

In some cases, simply improving diet. supporting digestion and restoring gut balance is enough to resolve symptoms.

For example, reducing sugar and processed foods can limit the fuel available to opportunistic bacteria, while improving digestion helps prevent fermentation.

This approach focuses on rebalancing the gut, rather than trying to eliminate bacteria.

Targeted antimicrobial treatment is usually only necessary when there is:

• Confirmed SIBO
• Significant opportunitic bacterial overgrowth on stool testing
• Persistent symptoms not improving with diet alone

Our Functional Medicine Approach to get rid of gut bacteria naturally

The approach that we take at our clinic, is not to focus on simply “killing bacteria.” Instead, we take a structured approach to restoring balance in the gut.

This involves:

1. Identifying the problem
Looking at your symptoms, history, and using testing where needed.

2. Targeting overgrowth (if required)
Using carefully selected treatments to reduce imbalance.

3. Rebuilding the microbiome
Supporting beneficial bacteria through diet and targeted support.

4. Addressing the root cause
Focusing on underlying drivers such as digestion, gut motility, and stress.

This approach helps move beyond short-term relief and supports more lasting improvements in gut health.

Patient Case Study

One patient came to us after trying oregano oil and berberine for over a year.

Although she experienced short-term relief, her symptoms kept returning and she admitted to feeling worse not better.

We worked in addressing her diet and her underlying motility issue as well as supporting her microbiome, her symptoms improved significantly within 4 weeks.

Key Takeaways

• Natural antimicrobials can reduce harmful bacteria
• They are not selective and may affect beneficial bacteria
• Killing bacteria alone is rarely a long-term solution
• Addressing the root cause is essential
  
  
  

FAQs

What naturally kills bad bacteria in the gut?
Garlic, oregano oil, berberine, and certain herbs can reduce harmful bacteria, but should be used carefully.

Does oregano oil kill good bacteria?
Yes, it is broad-spectrum and can affect beneficial bacteria.

How long does it take to rebalance gut bacteria?
Most patients see improvement within 4–12 weeks when the root cause is addressed.

Conclusion

While natural compounds can reduce harmful bacteria, the goal should not be to “kill bacteria,” but to restore balance within the gut.

This is where a functional medicine approach makes the biggest difference.

If your symptoms are ongoing or not improving despite diet and supplements, it may be worth looking a little deeper.

Testing and a personalised approach can help identify underlying imbalances and guide the most appropriate next steps.

If you would like support with this, you can book a consultation at our sister clinic ibs-solutions.co.uk to discuss your symptoms in more detail.

Author – Victoria Tyler BSc Hons MBANT

Victoria Tyler owns and runs two busy clinics : Nutrition and Vitality and the IBS and Gut Disorder Clinic.

Nutrition and Vitality, along with the IBS and Gut Disorder Clinic, were founded with the goal of helping patients alleviate IBS symptoms by uncovering and addressing the root causes of their digestive issues.

As a Registered Nutritional Therapist, Victoria holds a BSc (Hons) in Nutritional Therapy and has trained with the Institute of Functional Medicine. She is also accredited by BANT and CNHC.

Before transitioning into health, Victoria earned a degree in Economics and an MBA, working with corporations including Canon and Vodafone. However, her own health challenges led her to pursue a career in Nutritional Therapy.

With a passion for learning, Victoria is committed to staying at the forefront of Functional Medicine. She helps patients manage IBS and other digestive disorders, including SIBO, Candida, and IBD, by identifying and addressing their root causes.

Victoria strongly believes that every symptom has an underlying cause, and there is always a solution to every health condition. To learn more, or to see patient reviews, visit Victoria’s profile on Google.

DISCLAIMER: The information provided in this article is intended for general informational purposes only and should not be construed as medical advice, diagnosis, or treatment. The products and methods mentioned are not a substitute for professional medical advice from a trained healthcare specialist. Always seek the guidance of your doctor or other qualified health professional with any questions you may have regarding your health or a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website. Use of the information and products discussed is at your own risk.

References

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