Not all bacteria are bad for you

Living within us are around 100 trillion bacteria - known as the microbiome - and 95 percent of them live in our gut.

Living within us are around 100 trillion bacteria - known as the microbiome - and 95 percent of them live in our gut.

Published Apr 2, 2013


London - As you scrub your hands with antibacterial soap and gargle with antiseptic mouthwash just think: each of us is more bacteria than we are human.

“People are generally surprised to learn that there are ten times more bacterial cells than human cells in our bodies,” says Professor Philip Calder, a nutritional immunology expert from the University of Southampton. “Actually, in terms of cell count, a person is 90 percent bacteria.”

Living within us are around 100 trillion bacteria - known as the microbiome - and 95 percent of them live in our gut. Other colonies are on our skin and in our respiratory tracts, mouths and genital areas.

Most are harmless and beneficial to us but there are bad bacteria with the potential to cause ill health - so why are we not permanently sick?

The secret lies in the balance of the bugs, which exist in a fragile ecosystem. Knock one out and the system goes haywire.

Imbalances in gut bacteria, for instance, have been linked with diabetes, obesity, autism, eczema, psoriasis, asthma and inflammatory bowel conditions such ulcerative colitis and Crohn’s disease. Latest research suggests the bacteria may even in certain cases cause the immune system to attack the coatings of nerves - causing the symptoms of multiple sclerosis.

Here, we take a look at the other findings being uncovered about the 2kg of bacteria that call you home…



It seems that the type of bugs you have in your body can affect mood. In one study, mice fed lactobacillus (‘gut friendly’ bacteria commonly added to probiotics) were less anxious. It is thought this is because the bacteria affect production of GABA, a brain chemical that has a calming effect.

Microbes make many chemicals that connect to the brain, says Professor Jeremy Nicholson, head of biological chemistry at Imperial College, London. “We don’t know much about them yet, other than they are constantly talking to us.”



It’s a common misconception that the cleaner the skin, the better - and the bacteria that live on our skin have an important role.

“If you wash your hands repeatedly, they dry out - this is partly because you wash away all the oils but also because you remove a large number of the bacteria that help maintain the skin’s condition,” says Professor Mark Fielder, a medical microbiologist at Kingston University.

“If you overuse detergents (soaps), some micro-organisms are removed and others become more dominant, which can lead to problems such as dermatitis.”

He says that acne may also be brought on by a change in the bacterial skin flora: “If some of the ‘good’ bacteria on the skin are killed off - for example, by antibiotics - this allows other bacteria to flourish.” These include the Propionibacterium acnes bacteria, which can lead to spots.



Everyone’s mix of bacteria is as individual as their fingerprints. But if you live with someone, they’ll probably have similar types of gut microbes as you because bacteria can be passed between people.

Professor Nicholson says: “Every time you kiss, for example, you exchange a million bacteria. So your gut microbiology becomes close to that of your loved ones.”



What bacteria you have may influence your chance of having a heart attack or stroke. People with atherosclerosis (fatty deposits in the artery walls that can break off and cause either condition) have different bacteria from those who don’t, a recent study published in Nature Communications revealed.

Last year Swedish researchers found major differences in the gut bacteria of stroke patients compared with those of healthy people. It’s thought the latter have more bacteria that produce carotenoids, a type of antioxidant that may protect against angina and stroke.



Don’t read this while you’re eating, but earlier this year a clinical trial showed that using donor faeces - rich in friendly gut bacteria - was more effective at clearing a recurrent infection than antibiotics.

Sixteen patients with recurrent C. diff - a bacterial gut infection that can cause severe diarrhoea - were given a “transplant” four times a day for four days. The only side-effect was mild cramping on the day of the infusion.

Eighty-one percent were cured, compared with just 31 percent of those given antibiotics instead.

Professor Calder says: “The faeces transplant is screened for harmful bacteria or viruses, and is performed by an enema tube or by putting a tube down through the nose into the intestine.”

The faeces are usually from people in the patient’s family, as this is easier and more “acceptable”, but they could, in theory, be from anyone. Lawrence Brandt, a professor of medicine and surgery at New York’s Albert Einstein College of Medicine, believes the treatment could work for other, non-gastro conditions, such as obesity and Parkinson’s.



Obese people have different bacteria from non-obese people. “The microbes found in the gut of an obese person are more efficient at pulling calories out of food,” says Professor Nicholson.

It is believed they are around 10 to 15 percent better but it is unclear if the bacteria changes as a result of someone becoming overweight or if the bacteria itself causes obesity. However, a study of mice found those who were given gut bacteria from obese mice put on more weight than those who got it from lean mice.

And Professor Nicholson says: “Interestingly, after someone goes through bariatric (obesity) surgery, their gut bacteria undergoes a change. This surgery also acts as a virtually instant ‘cure’ for type 2 diabetes, and there is emerging evidence that gut bacteria are implicated with this, too.”



Gut bacteria can determine the way we react to medication. “They metabolise drugs and change their absorption and toxicity,” says Professor Nicholson. “Individual variations in bug activity change how drugs work - both good and bad effects are possible.”

This may help explain why people react differently to drugs - or why medication sometimes stops working for someone for whom it has previously been effective.



Researchers are looking at whether gut bacteria - in particular Escherichia coli (E. coli) - are linked with colon cancer.

Dr Barry Campbell, a physiologist at Liverpool University, says some E. coli strains can live harmlessly in the gut of healthy people, but problems arise when there is inflammation - which happens from time to time when the gut is damaged.

“This seems to reduce the numbers of beneficial bacteria and increase the presence of E. coli,” he says. “We know inflammation increases the danger of cancer in the bowel but we now believe inflammation increases the numbers and virulence of specific bacteria that support cancer development - it’s a whole new area of research.”



During the first three months of pregnancy, the mother’s bacteria change to pass on beneficial bugs to her baby as it is born, according to a study published in PLOS ONE.

Strains such as Lactobacillus johnsonii - normally found in the upper gastric tract, where it helps with digestion - become abundant in the vaginal tract, while others decrease. During delivery, the baby picks up the bacteria, which is why babies born naturally have a mix of bugs often found in the gut while those delivered by caesarean have a mix of bugs usually found on the mother’s skin.

The gut bacteria are thought to help prime the newborn’s immune system.

A recent US study at the Henry Ford Hospital in Detroit of 12 578 babies over two years found those born by caesarean were five times more likely to develop allergies than those delivered naturally.



A 2011 study found children in Burkina Faso, West Africa - who have a diet low in animal protein and fat - had a different make-up of gut bacteria from those in Florence, Italy - who eat a diet rich in animal protein and sugar, and low in fibre.

“There is the possibility that by eating a diet higher in fat or carbohydrate, we can influence our health. The difficulty is identifying the type of bacteria present and their role,” says Professor Calder.

“You can’t oversimplify it, as it seems to be the mix of bacteria that is important.” - Daily Mail

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