Complex Human Relationship With Bacteria
The adult human gastro-intestinal tract (GI tract) consists of mainly the stomach and the intestines (small and large). It is 20ft (5m) long. In it live a variety of bacteria (germs) that are single-celled microscopic organisms, one of the basic forms of life. The bacteria are neither animals nor plants. Some of them can survive in boiling and freezing temperatures and can be either beneficial or harmful to human beings.
We know very little about the 10 trillion bacteria that live in our GI tract. They are normally called “microflora”, but it is a misnomer as they are not plants though in the beginning they were regarded as microscopic plants. They are generally useful to us but in certain situations they can be quite injurious to our health. For example: Clostridium difficile bacteria live harmlessly in the gut of many people. Their number is kept in check by other inhabitant bacteria in our gut. However, if their number increases they can cause diarrhoea and other symptoms because of the toxins they produce. This can happen when antibiotics destroy normal bacteria but not them.
While I was in school and college it was customary in Imphal for doctors to prescribe vitamin B-complex along with an antibiotic, presumably to keep the gut bacteria healthy. It was not a practice I found anywhere else in India or abroad.
Most doctors know that antibiotics especially the broad-spectrum penicillin and amoxicillin can cause diarrhoea, especially in children, by destroying the gut flora. Once the antibiotic is discontinued the diarrhoea stops by itself. Infant diarrhoea in the West and the States, is treated simply by giving oral fluid with electrolytes as almost all of them are caused by Rotavirus or milk or fluid intolerance.
In the UK and the USA, probiotic supplements in the diet ie live bacteria and yeasts that are good for you, especially for your digestive system, is very popular. Its use tripled during 1994-2003. Nutritionists and food manufacturers recommend them for a calm stomach and to boost the body’s immune system. The commonest supplement foods are yoghurts containing lactic acid bacteria – the largest group of probiotic bacteria in the intestine. However, there is limited supporting evidence that probiotic supplements help overall good health.
In 2008, the United States National Institute of Health, a government funded organisation, launched the Human Microbiome Project, designed to identify the microbial flora that are associated with healthy and diseased humans. The project is dedicated to sequencing the genomes that is the genetic content of the 900 or so species of microbes found in the body.
In 2010, scientists found how to alter the microbe population of the gut in a spectacular fashion. One 2-year old child at Massachusetts General Hospital in Boston, America, was suffering from life-threatening diarrhoea caused by a strain of Clostridium difficile. Nothing the paediatricians could do seemed to work and the young life was draining away in front of the doctors’ eyes.
As last-resort, they used an antibiotic called vancomycin, but it had failed. So, they turned to experimental, unlicensed antibiotics, but these too had no effect. Running out of time, they decided that rather than trying to get rid of the bacteria that were causing the illness, they
introduced more bacteria found in faecal matter of a healthy individual. Within weeks the child made a full recovery.
The incidence is bizarre, but it has brought out the most important knowledge that the bacteria living in our own human bodies play in human health. They make essential amino acids and vitamins, help regulate our immune response and break down starches and proteins. The total number of species is thought to be in thousands.
Since the beginning of the year 2000 there has been a resurgence of C difficile infection in the US and Europe as a major cause of hospital morbidity. The success of faecal microbiota in restoring “colonisation resistance” for patients with multiple recurrences of clostridium difficile infection, as an adjunct to antimicrobial treatment, is now undergoing trials in the Massachusetts Hospital and others.
Prof Weinstock, a geneticist at Washington University in St Louis, Missouri, explains: millions of years of evolution have seen man and microbe come to depend on each other to a remarkable degree. Their study shows that trillions of microbes inhabit the human body, occupying virtually every nook and cranny. And most of the time, this relationship is a friendly one, with microbes helping to digest food, strengthen the immune system and ward off dangerous pathogens.
But despite their prominent roles, researchers have understood little about which microbes reside in specific sites of the body. Now, a consortium of some 200 U.S. scientists at Washington University School of Medicine in St. Louis and elsewhere, report findings from the most comprehensive census of the microbial make-up of healthy humans.
The research, published in Nature and in several Public Library of Science (PLoS) journals, offers new details and even some surprises.
For example, the researchers found that even healthy people typically carry low levels of harmful bacteria in and on their bodies. But when a person is healthy, these pathogens do not cause disease but simply coexist in an abundance of beneficial microbes. Now, scientists can investigate why some pathogens can suddenly turn deadly, an endeavor that will refine current thinking on how microorganisms cause disease.
The researchers expect to see some important developments in the next few years against a variety of cancers, particularly of the digestive system, as well as Crohn’s disease, psoriasis, and stillbirths due to bacterial vaginosis.
They will also be researching on the bacteria that live inside our mouths as evidence builds up that they can cause inflammation in other parts of the body, and damage organs such as the heart.
Doctors have known for a long time that streptococcal bacteria that live in human mouth causing sore throat, often destroy heart valves, resulting in heart failure. In the West, because of wide-spread use of antibiotics for sore throat, sometimes caused by streptococcal bacteria and often by virus, the disease known as rheumatic fever that was very common when I was a medical student, is now unheard of.
In the 1980’s, the discovery of a bacterium, Helicobacter pylori that lives under the mucosal lining of the stomach and duodenum, causing peptic ulcer, has revolutionised the treatment of this disease by its eradication with antibiotics. Until then, the stomach ulcer was thought to be due to excess of hydrochloric acid and bile in the stomach.
One important link was dramatically demonstrated in July 2010 when researchers in New York University, published the first long-term evidence that gum disease increases the risk of Alzheimer’s disease, associated with dementia in older people (different from senile dementia of old people).
Alzheimer’s disease which of late, has become quite well known, is due to a degenerative condition of the brain. It is suggested that the activity of some bacteria in the gums contributed to brain inflammation and nerve cell destruction.
Meanwhile, British scientists at Imperial College in London, have revealed that our lungs are teaming with different species of bacteria, throwing into question the long held belief that our lower airways are sterile. They have found a few species of bacteria in the lungs of asthma patients, which are often found in throat swabs taken from asthma-prone babies. They think they are on the verge of finding a large group of microbes that are linked to asthma.
Recent research has also discovered that viruses inside the cells of bacteria also play a part in the complex human-microbe relationship. The suggestion is that these viruses could be inserting their own genes into those of the bacteria that live in our gut and other organs, thereby influencing their behaviour.
Finally, Prof Weinstocks says: “looking to the future, I can imagine in 15 years’ time, the goal will be to look at a person’s microbes and ensure the right balance is there and make adjustments if necessary, to keep that person in optimal health.”