Probiotics: studied strains, when they help, when they don’t

Probiotics are the pharmacy category with the biggest gap between advertising and clinical evidence. "The balance of the gut flora", "immunity", "a healthy colon" — slogans repeated without a reference to the specific strain. And the strain matters enormously: Lactobacillus rhamnosus GG and Lactobacillus casei Shirota have consistent studies; a "generic probiotic 10 billion CFU" has almost none.

The definition that matters

According to the WHO/FAO definition from 2001, updated by ISAPP 2014: live microorganisms that, administered in adequate amounts, confer a health benefit on the host. Three key elements: live, an adequate amount (usually ≥10⁹ CFU/dose, but strain-dependent), a demonstrated benefit (through studies on that specific strain).

The strains with the best evidence

Products on the Romanian market — examples

• Enterol 250 — pure S. boulardii. The first choice for antibiotic-associated diarrhoea.
• Linex Forte — L. acidophilus + Bifidobacterium — a classic combination.
• Bioflorin — Enterococcus faecium SF68 — acute diarrhoea.
• BioGaia ProTectis — L. reuteri DSM 17938 — infant colic.
• Florasan-D — multi-strain.
• Multilac, Yovis — multi-strain combinations.
• Yoghurt with probiotic cultures (Activia, Actimel) — relatively small doses, a dietary support, not a therapeutic equivalent.

All are OTC. Prices differ significantly — Catena, Dona, Help Net, Farmacia Tei, Dr.Max, Mattca, Springfarma. Check on HartaFarmacii.

The indications with real evidence

1. Antibiotic-associated diarrhoea (AAD)

Cochrane meta-analyses: S. boulardii and L. rhamnosus GG reduce AAD by ~50%. Start within the first 48h of the antibiotic, continue for 1-2 weeks after the last antibiotic. A 2-hour gap between the antibiotic and the probiotic (the antibiotic could destroy the strain).

2. Acute infectious diarrhoea in children

Reduces the duration by ~24 hours (S. boulardii, L. rhamnosus GG, L. reuteri). Combined with oral rehydration — the gold standard.

3. Infant colic

L. reuteri DSM 17938 — the Sung et al. meta-analysis — a significant reduction in crying time. A clearer benefit in breastfed infants.

4. Irritable bowel syndrome

A modest, strain-variable benefit. L. plantarum 299v, Bifidobacterium infantis 35624 (Align) — more studied. It requires personal trials of 4-8 weeks; what works for one does not for another.

5. Inflammatory bowel disease (IBD)

VSL#3/Vivomixx — pouchitis after colectomy for UC; maintenance of remission. Not first line in active Crohn's.

6. H. pylori eradication

Adding S. boulardii to triple therapy slightly increases eradication and reduces side effects.

Poorly supported or unproven indications

• Generic "immunity" — marginal evidence, small and inconsistent effects.
• Bacterial vaginosis — some evidence, but the first line remains metronidazole/clindamycin.
• Atopic eczema — inconclusive meta-analyses.
• Gut "detox", generic "debloating" — a myth.
• Weight loss — firm evidence is non-existent.

How to read a probiotic label

1. The complete strain name: genus + species + subspecies / code (e.g. Lactobacillus rhamnosus GG, not just "L. rhamnosus").
2. CFU guaranteed at the expiry date (not just "at manufacture").
3. Studies cited on that strain — if the brand cannot reference anything, be sceptical.
4. Storage conditions — in the fridge or at room temperature (microencapsulation?). S. boulardii is heat-resistant; many Lactobacillus and Bifidobacterium need refrigeration.

Safety and contraindications

Probiotics are generally safe in healthy people. Caution with:

• Immunocompromised patients (chemotherapy, transplant, advanced HIV) — a rare risk of bacteraemia/fungaemia with the probiotic strain.
• A central venous catheter — a risk of fungaemia with S. boulardii.
• Severe acute pancreatitis — the PROPATRIA 2008 study suggested increased mortality with a combined probiotic. Avoid in the acute scenario.
• Premature infant — a specific strain selection, a medical indication.

Frequently asked questions

If I eat yoghurt daily, do I still need a pharmacy probiotic?

For general health — yoghurt is enough. For a clinical indication (AAD, IBS), you need the proven strain and dose.

Why S. boulardii and not Lactobacillus with an antibiotic?

Because S. boulardii is a yeast — insensitive to the bacterial antibiotics. It passes through unaltered.

Can I take a probiotic indefinitely?

Generally yes, but without a clear indication the benefit falls. For AAD — the antibiotic course + 1-2 weeks.

Does the probiotic "colonise" the gut?

Not permanently. Probiotic strains transit the gut — they disappear within 1-3 weeks after stopping. The effect is rather transient and through local immune modulation.

Why "synbiotic"?

A combination of a probiotic (microorganisms) with a prebiotic (fermentable fibres, e.g. inulin, FOS). The logic: food for the bacteria. Modest additional evidence.

A probiotic for a child on an antibiotic?

Yes. S. boulardii (Enterol) or L. rhamnosus GG. They reduce paediatric AAD.

The microbiota: what we know and what we don't

The human gut hosts 10¹³-10¹⁴ microorganisms with >1000 bacterial species, plus archaea, fungi, viruses. Microbial diversity is associated with metabolic health, immunity, behaviour (the gut-brain axis). What we do with this knowledge is still an open question.

Reasonably confirmed things:

• Antibiotics reduce diversity for months to years.
• A diet rich in plant and fermented fibres (yoghurt, kefir, sauerkraut, kimchi) supports diversity.
• Chronic stress and poor sleep affect the composition.
• Certain probiotic strains modulate local inflammation and gut permeability.

Things still uncertain:

• "Dysbiosis" as a clinical diagnosis — a popular concept, an unclear definition.
• Commercial microbiome tests (uBiome, Viome, etc.) — uncalibrated results, not translating into therapeutic recommendations.
• "Personalised" probiotics — still a research field.
• Faecal microbiota transplant — demonstrated effective only in recurrent C. difficile; active research for other indications.

Probiotic vs. prebiotic vs. postbiotic vs. synbiotic

Practical cases — what you should take

• Adult starting a 7-day Augmentin course: Enterol (S. boulardii) 250 mg twice a day from day 1, continued for 1-2 weeks after the last antibiotic dose. A 2-hour gap between the antibiotic and the probiotic.
• 6-week-old infant with colic: BioGaia ProTectis (L. reuteri DSM 17938) 5 drops/day, 3-4 weeks. Check weight, breastfeeding, technique.
• A child with acute diarrhoea at daycare: S. boulardii (Enterol 100 mg/ml solution) or L. rhamnosus GG, plus oral rehydration.
• Adult with diarrhoea-type IBS: a 4-8 week trial with Bifidobacterium infantis 35624 or L. plantarum 299v; document the symptoms, assess the real benefit.
• International travel with a risk of "traveller's diarrhoea": S. boulardii 250 mg/day starting 5 days before and throughout the trip.
• Patient on a chronic PPI + metformin, a 65-year-old man: not a first indication for a probiotic; check B12 annually, consider it in intermittent diarrhoea.

Myths debunked

• "The probiotic cleans the colon" — the colon does not need to be "cleaned"; purgatives are not probiotics.
• "The probiotic treats acne" — minimal evidence for topical and oral; some studies suggest a modest benefit, not first line.
• "Activia yoghurt makes you regular every day" — the marketing was sanctioned by the FTC in the US for exaggerated claims; the transit effect is real, but of a modest magnitude.
• "Probiotics are destroyed by gastric acid" — the nuanced truth: many strains are sensitive, but microencapsulation and modern forms (gastro-resistant tablets) increase survival. S. boulardii is intrinsically resistant.
• "The more billions of CFU, the better" — above a strain-specific threshold, more does not equal more effective.

How to check a product before buying

1. Identify the complete strain on the packaging — genus, species, sub-code (L. rhamnosus GG, S. boulardii CNCM I-745, B. infantis 35624).
2. CFU guaranteed at the expiry date, not just at manufacture.
3. Specific indications — if the claim is generic ("gut health"), suspect.
4. Refrigeration needed? Check the instructions; transport in a car in summer at 35°C can destroy sensitive strains.
5. Cited studies — search PubMed for the strain name + the indication.
6. Price per active dose — compared on HartaFarmacii between the RO chains.

Sources

• ISAPP — probiotic definition and classification 2014/2019
• Cochrane — Probiotics for the prevention of pediatric AAD; for C. difficile (Goldenberg et al.)
• WGO (World Gastroenterology Organisation) — Global Guidelines Probiotics and Prebiotics 2023
• ESPGHAN — pediatric probiotic guidelines
• Sung et al. — L. reuteri for infantile colic meta-analysis
• ANMDMR — SmPCs for products authorised as medicines (Enterol, Linex Forte etc.)
• EMA — review on probiotic medicines
• AGA — practice guidelines on probiotics in gastrointestinal disorders 2020

Curat de echipa HartaFarmacii — informații sintetizate din surse publice (ANMDMR, EMA, BNF, CNAS), revizuit periodic. Acest material nu înlocuiește consultul medical.