Probiotics: dead or alive?

Counting the studies that have been done on probiotics is like counting the organisms in a gram of yoghurt.

Probiotics are live microbial ingestible supplements that can benefit the host (ingesting) organism by favourably altering its intestinal microbial balance.1 Given the assumption that these microbial supplements must be living, substantial research and development has been dedicated to processes and agents that can prolong their stability and viability throughout the food, beverage and dietary supplements value chain. These include cryo-preservation; prebiotics; microencapsulation; and novel delivery vehicles such as protein-based microparticles, and sausages, along with strain selection.2,3,4,5

But do the organisms need to be alive to be effective?

A number of basic and clinical research studies have been conducted with a heat-killed, freeze-dried, human gut-derived strain (LB) of Lactobacillus acidophilus (Lacteol Fort, Homdan, France, first isolated in 1907) with a fermented culture medium. Earlier studies conducted among paediatric and adult populations showed efficacy in acute diarrhoeal episodes.6,7 A double-blind, placebo-controlled crossover trial in a population of 18 inflammatory bowel disease patients revealed significant clinical efficacy with a daily dose of 10 billion organisms taken twice daily.8 Although a research-validated symptom score was not used, the crossover design (with a two-week washout) augments the rigor of the trial.

A more recent study among 73 paediatric patients (ages 3-24 months) with acute watery diarrhoea and mild to moderate dehydration revealed that a dose of 10 billion LB cells, taken as Lacteol Fort (twice daily), produced significant reductions in the duration of diarrhoea, especially among infants who had not received prior antibiotic therapy.9 The LB strain/culture medium that comprises Lacteol Fort exhibits gut cell adhesive and pathogen excluding properties, which appear to be thermostable.10,11

Collectively, these data demonstrate a 'probiotic' effect with dead organisms. The ideal assessment would be a head-to-head comparator study assessing a heat-killed strain against a live probiotic strain.

One study did just that. It was a multi-centre, randomised, open-label four-week study that assigned 137 adults with chronic diarrhoea to receive Lacteol Fort (10 billion organisms twice daily) or a live Lactobacillus acidophilus chewable tablet that contained 400mg of skimmed fermented milk per tablet (five tablets thrice daily; strain not specified and viability not validated; Lacidophilin brand, Tai Ge Pharma, China).12,13 The Lacteol group showed significantly superior efficacy in symptom scores and overall efficacy.

The obvious major weaknesses of this study include the complete lack of characterisation of the 'live' probiotic strain, the absence of a placebo control, and the lack of blinding. A definitive and rigorous head-to-head comparator study is warranted, including assessment of the efficacy of the Lacteol Fort fermented culture medium alone.