I have decided the survival of the fittest is not a very fair concept. Whoever dreamt that one up should try surviving in the human gut.

I am one of around 400 species of tiny microorganisms living inside the human gastro-intestinal tract.

In healthy humans, most of us are friendly types and we are also known as probiotics.

The bifidobacteria and lactobacilli are among the most commonly known.

Each probiotic strain has developed its own little niche, supporting its host by improving the gut's ecosystem.

We carefully patrol our patch and try to prevent pathogenic (disease-causing) bacteria, parasites and yeasts from taking over.

I see no reason for these punks to invade our space and breed continuously so we are crowded out.

Beneficial bugs deserve some respect, for we work around the clock to keep our owners optimally healthy, unlike the other lot who like to create persistant bellyache.

Just take a look at some of the jobs we do: We aid digestion by breaking down proteins and sugars and help to evacuate the bowel by promoting smooth muscle contractions.

We produce certain B vitamins and vitamin K (important for healthy bones) and increase the bioavailablity of mineral salts, including calcium.

We boost immune function and increase resistance to infection by coating the intestinal wall and secreting special agents to make it less permeable.

We even manufacture biochemical weapons of our own to fend off the yobs responsible for stomach upsets, yeast infections and immune-related problems.

Ever since Louis Pasteur discovered some of us have the potential to cause serious illness, our human hosts have regarded us with suspicion, trying to wipe us all out with antibiotics and other drugs.

Chronic stress, chemicals such as chlorine and poor dietary habits (refined food, excess sugar and meat) have also resulted in heavy losses on our side.

Meanwhile, the bad guys are becoming increasingly resistant.

Will we surrender? Not a bit of it.

A hundred years ago, Elie Metchnikoff, a researcher working at the Pasteur Institute in Paris, realised human health largely depends on the condition of our intestines.

He noted that Bulgarians drink fermented milk and have a remarkably long and healthy lifespan.

Since then, microbiologists and food scientists have been trying to find ways of recolonising the gut with "friendly" bacteria to enhance immunity and prevent disease.

Live yoghurt is a great natural source of beneficial bacteria but daily consumption may not be sufficient to replenish the intestines.

How much an individual requires depends on the extent of microbial depletion and presence of harmful species.

Nutritionists routinely advise supplementing with a full spectrum of "friendly" bacteria in capsule or powder form.

Probiotics are perfectly safe for pregnant women, babies, children and pets.

In fact, your good health just wouldn't be the same without us.