The ideas that certain microorganisms may have beneficial health effects beyond their nutritional value, or that 'good' bacteria could conquer 'bad' bacteria, are not new.

Russian zoologist and microbiologist Elie Metchnikoff (1845-1916), who shared the 1908 Nobel Prize for Physiology and Medicine with Paul Ehrlich for the discovery of phagocytosis by cells of the immune system, developed an interest in human longevity and spent the last years of his life advocating the consumption of lactic acid bacteria. Metchnikoff was the first to propose the cellular theory of immunity.

With credentials like those, why have mainstream clinicians largely ignored probiotics, the term, meaning 'for life', given to health-producing bacteria and yeasts?

I am well placed to supply the answer as I am one of those clinicians, having been engaged in clinical immunology research for about 25 years. Until recently, I would have counted myself among the vast majority of sceptics within my peer group when it came to the so-called benefits of probiotics.

The reason for such scepticism is that clinical researchers are trained to assess the quality of the available evidence before accepting any claims regarding a new drug or treatment. It is critical that we provide our patients with the best available health care, which depends in turn on our using therapies which have been proven in rigorous clinical trials and which have undergone close scrutiny from regulatory agencies such as the US Food and Drug Administration and, in Australia, the Therapeutic Goods Administration.

The problem is that products based on probiotics are not subject to such scrutiny. They are not classified as drugs and are consequently available over the counter at pharmacies or off the shelf at supermarkets as components of 'functional foods' and 'nutriceuticals'. This lack of regulatory requirements for probiotics opens the way for unsubstantiated claims to pass unchallenged. No wonder there were so many doubters in the medical profession.

Conversion

But I, for one, have changed my mind. I am a convert. Through Good Health Solutions, a workplace health and well-being company, we have commenced recruiting subjects for a clinical trial on the potential for probiotics to enhance the effectiveness of flu vaccines and I have accepted a position as director of Australian biotechnology company Probiomics, whose business is the development of probiotic products to treat a variety of diseases.

I first heard about probiotics and their effects on the immune system through a colleague, Dr Peter French, innovation and business development manager of Probiomics. My conversion came when I reviewed the company's scientific data.

French showed me convincing evidence that Probiomics' proprietary strain of lactobacillus, called PCC L.Fermentum, had actions throughout the body, rather than in the gut alone, which could be beneficial in a number of diseases of immunity and inflammation. The data were published in peer-reviewed scientific journals. As far as I was concerned, here was the evidence that had been lacking.

It has only been in recent years that such rigorous evidence has become available for the health benefits of probiotics, and then only for relatively few members of the large group of lactobacilli microorganisms - in excess of 400 - that are described by this term.

One thing that has become patently clear is that not all probiotics are the same, even within one type of organism, such as the lactobacilli. For example, they differ in their ability to survive in the acidic environment of the stomach, to colonise the gut and to produce beneficial responses in the regional immune system of the gut.

Most of the probiotics that have been studied scientifically have actions in the gastrointestinal tract, where they have been found to stimulate local immune reactions to improve the symptoms of diarrhoea caused by pathogen infections and conditions such as irritable bowel syndrome.

A truly unusual finding with PCC, and a key point of difference, is that it produces systemic effects on the immune system when taken orally. This potent response was unexpected. It was this feature of PCC that so captured my interest that it set me off on a new direction in my career.