Probiotics deliver benefit in a variety of different ways some of which are better understood than others. Competitive exclusion has already been covered elsewhere on this blog and is the process whereby ‘good’ bacteria crowd out the ‘bad’ or pathogenic bacteria through sheer weight of numbers. Also previously mentioned is the complicated process of immunomodulation whereby some probiotic bacteria interact with the human immune system to reduce inflammation and so improve the symptoms of certain digestive conditions. A third mechanism of action revolves around particular characteristics of certain bacteria which release substances which in tiny quantities are harmless to humans, but toxic to other bacteria nearby including pathogenic bacteria.
For this mechanism to be effective, probiotic bacteria with a particular affinity for attaching to the surface of the bowel are required. Once attached (by tiny fingers known as fimbria) and depending on the species or strain of bacteria involved, substances including lactic acid, hydrogen peroxide and other bacteriocins (toxic to bacteria) are released which directly attack pathogenic bacteria preventing them from gaining a foothold.
A typical bowel contains trillions of bacteria from hundreds of different species, so the number of possible interactions between one species and another or several others is vast. It’s true to say that no two bowels are the same, and everyone on the planet will have a subtly different population of bacteria occupying their digestive tract, this presents a problem when deciding on what probiotic bacteria are the best to add since this might be different from one person to another
One way around this is to choose a probiotic which contains multiple strains of bacteria so that there is more than one chance of adding a strain which will be beneficial for that particular individual. It’s important that the probiotics are alive and healthy when consumed to give them the best possible chance of passing through the stomach and into the lower digestive tract where they can attach to the gut wall and begin to divide.