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Symbiotic relationship between Man and Microbes

The gut of humans and animals is verily a microbial ecosystem

Until about 150 years ago, we did not realize that there are over a million life forms on earth, which we could not see with our naked eyes. Thanks to Louis Pasteur, Robert Koch and others, and the use of microscopes as standard equipment in science laboratories, these organisms came to be visualized, identified and classified as (what else) microorganisms or microbes.

First impression

From the very start, they were considered a nuisance-disease-causers and even death-dealers. The eponymous term, Pasteurization, destroys these microbes and makes food and milk safe from their ill effects. Even before Pasteur, Edward Jenner found a way to prevent small pox, through not quite knowing that the villain was a virus, a microbe. And it was Joseph Lister, another Englishman, who showed that the simple act of doctors washing and scrubbing their hands could prevent thousands of deaths in hospitals; this simple act offers antiseptic protection.

Are all microbes a disease spreading nuisance? That there are some which actually help us came to be known by about 1910 or so. The Russian Nobelwinner biologist Ilya Mechnikov was researching on why many Bulgarian peasants live longer and healthier than others, and suggested the secret to be the yoghurt that they consume.

Yoghurt beneficial

Yoghurt contains the bacterial family called Bifido bacterium (earlier called lactobacillus bifidus), which colonize our gut and lower intestines. They not only help us in digesting milk and related food, but also reduce stomach disorders, allergies and even some tumours.

These gut bacteria live in a mutual give and take relationship with us. Such symbiosis has earned the title probiotic agents. Indeed, the stomach upset that we experience when we take antibiotics like erythromycin or penicillin is because these drugs not only target the disease-causing germs, but on the probiotic ones in our body as well. Yoghurt and cheese are given to repopulate our bellies with the bifidus and in severe cases a dose of lactobacillus itself.

It is not just us, Ruminants such as cattle depend for their digestion on the bacteria, fungi and protests that colonize their second stomach for digestion. These help to digest cellulose and several other materials that the cattle have eaten.

Indeed, the gut of animals and humans is verily a microbial ecosystem-akin to a tropical rainforest. Latest estimates reveal that there are hundreds of 200 such microbes colonizing our body.

And we seem to need them just as much for our lives, as they do us. This has led some scientists to suggest that we humans have actually coevolved with many of these essential in-house bacteria. When the human genome was read out, letter by letter, in its3 billion long vocabulary, it was found that several hundred genes in us came actually from bacteria, and hundreds more from viruses.

Not only have we had microbes colonizing our bodies all these years, helping our physiological machinery works smoothly, but we have even snatched off some of their genes and incorporated them into our genome as part of our heritage. How, then, are we different from plants which depend on bacteria (called rhizobium) that offer them nitrogen in an assimilable form? The rhizobium in turn gets its oxygen in assimilable form from the plant.

Such a given and take scenario lets us ask the question: Is bad microbes that causes us trouble always bad, or does it have any redeeming quality at all?


A few years ago, Drs Barry Marashall and Robin Warren showed that stomach and duodenal ulcers are caused not just by stress or by eating hot food alone, but actually because of a bacterium colonizing our gastric system, called Helicobacter pylori.

Now comes a twist to the story. Dr Martin Blaser of the NYU School of Medicine finds that H.pylori could even be helpful to us. It has been living in mammalian stomachs since 150 million years ago, as a symbiont. other materials that the cattle have eaten.

Its actual role, he claims, is to regulate the acidity levels in the stomach, in a way that is helpful both to its host and to itself. It is when one of its genes (called cag) that is activated then toxicity occurs, provoking ulcers.

In a sense then, H.pylori, acts as a regulator or switch. In addition, it appears or switch. In addition, it appears to boost up our immune system to fight other bugs.

Blaser's analysis

Blaser's analysis shows that children infected with H.pylori are far less likely to have asthma and hay fever than those who have been given routine antibiotic treatment for such things as ear infections.

Thus H.pylori is not all bad: it has some saving grace too. The trick is not to annihilate it with antibiotics but control its level. Come to think of it – this is no different from our NRI cousins, whose children fall sick the moment they come here. Their bodies are not as well immune-primed with the microbes abundant in the Indian air and water as ours are.

Given a couple of months here, they can become as resistant as we.

SOURCE : The Hindu, September 18, 2008.

ENVIS CENTRE Newsletter Vol.6,No 3 September 2008 Back 
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