The generation time of a bacterium is defined as the time taken by it to double its numbers. Whether a bacterial species can work very fast has to do largely to its generation time. One of the proposed modes of action of the probiotic bacteria to exert its beneficial effects is to have a rate of proliferation greater than that of its colonial competitors. Once that is done it can easily achieve its goal to flourish rapidly and outnumber the undesirable or pathogenic bacteria, the so called ‘bad bugs’ of the body. Generally, there are many strains of Lactobacillus and Bifidobacterium that have a very short generation time. The average doubling time of the species of most of these bacteria is mostly in the range of 2-3 hours in the intestinal tract. This is a short enough time to get growth within the food as it moves along through the digestive system. However, there are strains that have a comparatively large generation time in vivo and consequently they are unable to show such colonization of food during its movement. Nonetheless, the bacteria with smaller doubling time can eventually aid in the digestion of the food and even prevent food poisoning. The trait can be put to use in patients with digestive malfunction. But before that a precise characterization of the growth characteristics of the probiotics in use has to be done.
Medium/substrate of growth:
Studies on the growth pattern of different strains of probiotics show a great degree of variability between their substrate specificity. e.g., under in vitro conditions, the lactulose utilization varies between strains of Lactobacillus and Bifidobacterium. Similarly, the growth rate is accelerated upon addition of amino acids or growth factors like ascorbic acid. This goes on to suggest that a mixture of different strains with varied utilizing ability of substrates that might be on offer can be used. The same policy can be adopted to overcome different adverse physiological conditions within the human body.
The form of the probiotics taken:
The probiotics are marketed in a variety of forms-live cells, heat inactivated or dead cells, parts of cells either as lyophilized powder or alongwith yoghurt, curd, whey. While the live cells with their own sets of added advantages may take time to come out of the lag phase as it may be in a lyophilized form and germinate to show their qualities. But once they start growing they can curve out a niche of their own making the conditions congenial for their growth while the same will be harsh for the survival of other microbes. e.g., the release of primary and secondary metabolites like fatty acids lowers the pH which is just perfect for the rapid growth of L. acidophilus but not for the unwanted pathogenic forms. There are several other similar factors that might provide the advantage to the live probiotics. While on the other hand some of the heat inactivated forms may provide quick relief because their action won’t be dependent on the availability of suitable environment. However, these dead cells can provide quick relief only in specific cases where these probiotics will not depend on long term signalling or colonization processes. Also, the cellular parts of the probiotics or their DNA can provide context-dependent fast alleviation of the problems. But these forms of probiotics although quite quick in exerting their beneficial effects, are not long term. To increase the shelf life of the probiotics, they are also available in microencapsulated or other coated types and release of the active form from such encapsulation would require more time than the normal heat inactivated lyophilized form.
Long term benefits of probiotics:
The probiotics with long term benefit takes longer to withstand the difficult conditions within the host body and colonize the gut, colon or the small intestine. The process may take days to months with the least reported being 2-3 weeks (Patel et al., 2012). Such long time is a reflection of the underlying mechanism that might be involved in the colonization process. A research group headed by Dr. Tabrizi at the Royal Women’s Hospital, Australia went on to determine the colonization process in the infants gut using high throughput quantitative polymerase chain reaction technique (qPCR). One of the major reasons behind the process involves the receptor-ligand interaction between the probiotics and the surface epithelia of the host GI tract. The research group of Patel found that probably the probiotic bacteria can modulate the regulatory intestinal barrier through Claudin 3.
The choice according to needs:
Therefore, the probiotics can work as early as 2-3 hours or may even take weeks. The choice then depends on the recipient of the probiotics according to the needs, i.e., whether the need is quick time short, term or prolonged and long term. e.g., the DNA or the cellular parts of the bacteria might provide quick relief but they may be treated foreign and excreted out rapidly by the host body although they can stimulate the immune system during that brief stay. some reports (Kurmann et al.) suggest that the probiotic products sold with the claim of health benefits should be provided in sufficient numbers (a minimum of 106 colony forming units (CFU)/ml of bacteria at the time of expiry with the suggested effective therapeutic dose per day is in the range of 108-109 cells. The safety aspect of the probiotics should be given the ultimate importance even when selecting a fast acting probiotic form-live or dead. Although with the well established live forms of probiotics, no or very little cases of side-effects have been reported. The dead inactivated cells need more thorough scrutiny before they can fit into the scheme of things as a safe probiotic. But the major concern at this moment might be with the use of cellular parts of probiotic cells including the use of DNA. The safety of the recipient with the use of these probiotic products are still under the scanner for which detailed research needs to be carried out in the future. So, both fast and slow acting probiotic types exist and the user needs to be educated before picking up one.