Given that each strain has specific attributes, different strains will offer varying benefits in different disease states. Thus, there is no one universal ‘probiotic’; each bacterium may help resolve symptoms in specific circumstances. It is also worth noting that generic health claims (such as improving well-being or health) made by probiotic manufacturers are unlikely to be substantiated by evidence. It is highly debatable whether good health can be further improved simply by modulating the gastrointestinal microbiota. The European Food Standards Agency (EFSA) is currently reviewing health claims made by food manufacturers so in future claims will not be allowed unless supported by sound evidence. As of 2013, no probiotic product has had a health claim approved by this body.

2.3.2 Safety

Probiotics in food products are generally regarded as safe in healthy populations, as demonstrated by their extensive use over centuries, with few reported adverse consequences. However, there are specific at-risk groups.

Probiotic bacteria can cause infective episodes if they translocate from the gastrointestinal tract to extraintestinal sites, such as regional lymph nodes, spleen, liver, bloodstream, heart valves or other tissues. Bacterial translocation is caused by a defective intestinal barrier, immunosuppression or gastrointestinal prematurity, and may result in bacteraemia, sepsis and multiple organ failure [5]. However, cases of probiotic administration leading to bacteraemia or fungaemia are rare. In 2003 an expert panel concluded that ‘Current evidence suggests that the risk of infection with probiotic Lactobacilli or Bifidobacteria is similar to that of infection with commensal strains, and that consumption of such products presents a negligible risk to consumers, including immuno-compromised hosts’ [6]. More recently, a systematic review of probiotics and nutritional support identified reports of 32 patients with infections of L. rhamnosus GG or Saccharomyces boulardii but this is most probably due to their extensive use rather than particular virulence [7]. The review identified the risks for probiotic-related infections as central venous catheter in situ and critical illness or impaired immune function leading to increased likelihood of bacterial translocation. Delivery of large doses of bacteria via postpyloric feeding tubes was also identified as a possible risk factor due to an increase in non-infectious complications [8] and mortality [9] in severely ill patients. Nevertheless, other trials have delivered probiotic bacteria via jejunal feeding tubes with no reported adverse events [7].

Three other recent reviews have explored the safety of probiotics in all patient groups [5,10,11]. L. rhamnosus GG, L. casei and Bacillus subtilis are species and strains that have caused bacteraemia and S. boulardii has caused fungaemia. Immunocompromised adults and neonates are identified as at risk, but there is no clear description of how to precisely define immunocompromise. The presence of a central venous catheter, impaired intestinal barrier, postpyloric delivery of the probiotic and cardiac valve disease are also highlighted as increasing the risk of infection. However, the reviews also note that infections are very rare and are not reported in most trials of probiotics, even those studying immunocompromised groups, such as those with HIV and neonates.