What Disease Does Lactobacillus Cause? Infections, Urine and Risk

In a healthy person, none is documented. Lactobacilli are normal residents of the gut, mouth and vagina, and in pooled trials live cultures caused no more adverse events than placebo. The rare exception is a bloodstream or heart-valve infection in someone already seriously ill: in a Finnish series of 89 patients with lactobacilli in their blood, 82% had severe or fatal underlying disease, and a review of over 200 reported cases worldwide found endocarditis and bacteraemia the most common. This page is one spoke of the Wellgard probiotics guide. It cannot interpret anyone's own test result; that is a GP's job.

Evidence at a glance

• Evidence: two case series (89 bloodstream cases; a review of over 200 reported infections); two urine studies (142 healthy women; 48 hospital isolates); safety data pooled from 36 antibiotic trials (9,312 adults) and 23 respiratory trials (6,950 people).
• Largest safety pool: 9,312 adults across 36 randomised trials, adverse events with live cultures the same as placebo (relative risk 1.00).
• Strongest measured outcome: mortality in Lactobacillus bacteraemia, 26% at one month and 48% at one year, predicted by the severity of the underlying disease (odds ratio 15.8).
• Not available in any study we found: a rate of infection per person taking a live-culture supplement; case series have no denominator.

Sources checked on 16 October 2026.

What disease does Lactobacillus cause?

Rarely, and almost only in people who are already seriously ill, lactobacilli reach the blood. In the Finnish series, 89 patients had Lactobacillus bacteraemia; the species was identified in 53% of cases, 25 of them L. rhamnosus. In 82% the patient had severe or fatal underlying disease, and the predisposing factors were immunosuppression, prolonged hospital stays and recent surgery. Mortality was 26% at one month and 48% at one year, driven by the underlying illness (odds ratio 15.8); antibiotics that the laboratory showed to be effective were associated with lower mortality (odds ratio 0.22). In 11 cases the strain was identical to a widely used supplement strain.¹

A 2005 review of over 200 reported Lactobacillus infections found endocarditis (infection of a heart valve) and bacteraemia the most frequent, with peritonitis, abscesses and meningitis also described; L. casei and L. rhamnosus were the species most often involved, and overall mortality was nearly 30%, higher where other bacteria were present in the same infection.² A systematic review in people with cancer, 17 studies and 1,530 people, found five case reports of bacteraemia or fungaemia linked to live-culture products and concluded they "may be a rare cause of sepsis".³ Set against that, 36 randomised trials in 9,312 adults on antibiotics found no more adverse events with live cultures than with placebo (relative risk 1.00),⁴ and 23 respiratory trials in 6,950 people found the same (1.02).⁵ Trials exclude the people in the case series, which is why both sets of numbers are needed.

What is Lactobacillus?

A genus of rod-shaped lactic acid bacteria. In March 2020 it held 261 species; that year, on whole-genome evidence, it was split into 25 genera. The emended Lactobacillus keeps the species adapted to living in people, including L. acidophilus, L. crispatus, L. jensenii and L. johnsonii, while L. rhamnosus and L. casei became Lacticaseibacillus and L. reuteri became Limosilactobacillus. The organisms and their trials are unchanged, and "lactobacilli" remains the group word for all of them.⁶ The species with trial records have their own pages: L. acidophilus, L. rhamnosus and L. reuteri; the lactobacilli of the vaginal flora are on what intimate flora is.

Is Lactobacillus good or bad?

Both questions have numbers. On the harm side, the case series above: rare infections in people with serious illness, and no documented case in a healthy adult taking a supplement. On the trial side, live cultures caused no excess of adverse events across 9,312 adults on antibiotics,⁴ and in the same analysis cut antibiotic-associated diarrhoea by 38%.⁴ The NHS page on live cultures, last reviewed November 2022 and past its review date, says that "for most people, probiotics appear to be safe", that there is "little evidence to support many health claims made about them", and that anyone with an existing health condition or a weakened immune system should talk to a doctor first.⁷ A 2015 safety review says the same: a long history of safe use, inconsistent safety reporting in trials, and theoretical risks "in susceptible individuals".⁸ What the trials found, outcome by outcome, is on do live cultures work.

Who is at risk of a Lactobacillus infection?

The people the case series describe: those whose immune system is suppressed, including by chemotherapy, corticosteroids or immunosuppressant medicines; people in hospital for long periods or after surgery; the critically ill; people with a central venous line or feeding tube; and premature or hospitalised babies.^{1, 3, 8} The NHS sepsis page, reviewed 14 May 2026, lists who has a higher chance of sepsis from any infection: a baby under 12 months, anyone over 75, pregnancy and the six weeks after it, an immune system weakened by a condition or by chemotherapy, corticosteroids or immunosuppressants, a wound, a skin infection or a urinary catheter.⁹ Those groups ask their clinical team before taking any live culture. The full list is on who should take care with live cultures.

What does Lactobacillus in urine mean?

Usually that the sample picked up normal vaginal bacteria on its way out. In a Lancet study, mid-stream urine from 142 healthy women grew lactobacilli at 10,000 per millilitre or more in 34.8% and at 100,000 or more in 20.2%; none had urinary symptoms or white cells in the urine, and the authors called them "commensals or contaminants" typical of the lower vagina. Urine taken directly from the bladder by needle in a further 44 women contained no lactobacilli at all, and 26 women with burning or frequency but no conventional pathogen carried lactobacilli at the same rate as the healthy women.¹⁰

There is an exception at the frail end of life. In a French university hospital, 48 patients over three years had L. delbrueckii grown from their urine; their mean age was 84 and almost all were women. 44% were diagnosed with a urinary infection, all with high counts (100,000 per millilitre or more), and the authors conclude the species "should be considered an actual pathogen when it is significantly found in the urine of predisposed patients with clinical and/or biological signs of infection".¹¹ The GP who ordered the test reads the result alongside the symptoms. The NHS urinary tract infection page, reviewed 11 July 2025, lists the symptoms (pain or burning when peeing, going more often or urgently, cloudy pee, blood in pee, lower tummy or back pain, a high or very low temperature) and the routes: a pharmacist for a woman aged 16 to 64 who is not pregnant; an urgent GP appointment or NHS 111 for anyone 65 or over, a child of 15 or under, a very high or low temperature, pain under the ribs, blood in the pee or a weakened immune system; 999 or A&E for confusion, drowsiness or difficulty speaking.¹²

What does Lactobacillus do for the body?

In the gut, lactobacilli are part of the resident community and a transient part of it when swallowed as food or a supplement; the fermented foods that carry them, by species, are on what foods are high in Lactobacillus. In the vagina, a flora dominated by lactobacilli is the healthy state, which is why a lactobacillus in a urine sample is more often reassurance than alarm.¹⁰ The benefit trials, as counts, sit on the Wellgard probiotics guide.

What we don't know

• No study gives a rate of Lactobacillus infection per person taking a live-culture supplement; the case series have no denominator.
• The Finnish series identified the species in only 53% of cases, so the share due to each species is uncertain.¹
• The urinary series comes from one hospital and one species; whether other lactobacilli behave the same way in frail older women is untested.¹¹
• Trials exclude the immunosuppressed and the critically ill, so the trial safety figures do not apply to them.⁸

Frequently asked questions

What is the most common disease caused by Lactobacillus?

Endocarditis and bacteraemia, in the 2005 review of over 200 reported cases; both occurred almost entirely in people with serious underlying illness.²

What is the treatment for a Lactobacillus infection?

It is a hospital matter. The team chooses antibiotics on the laboratory's susceptibility results; in the Finnish series, antibiotics shown to be effective in the laboratory were associated with lower mortality.¹ Sepsis is managed in hospital, and the NHS says to call 999 or go to A&E for the symptoms its page lists.⁹

What happens if you have too much Lactobacillus?

No clinical condition of that name exists. Swallowed lactobacilli pass through the gut rather than settle, and in the vagina lactobacillus dominance is the healthy state.¹⁰

Can you catch a Lactobacillus infection from someone else?

The case series describe infections arising in seriously ill patients from their own flora or, in 11 of the 89 Finnish cases, a supplement strain they were taking; none describes spread from one person to another.¹

Sources

1. Salminen MK, et al. Clinical Infectious Diseases, 2004. Case series of Lactobacillus bacteraemia, 89 patients, Finland. PubMed 14679449.
2. Cannon JP, Lee TA, Bolanos JT, Danziger LH. Pathogenic relevance of Lactobacillus: a retrospective review of over 200 cases. Literature review of case reports. European Journal of Clinical Microbiology and Infectious Diseases, 2005. PubMed 15599646.
3. Redman MG, Ward EJ, Phillips RS. The efficacy and safety of probiotics in people with cancer: a systematic review. Systematic review, 17 studies, 1,530 people. Annals of Oncology, 2014. PubMed 24618152.
4. Liao W, et al. Probiotics for the prevention of antibiotic-associated diarrhea in adults. Pooled analysis, 36 randomised trials, 9,312 people. Journal of Clinical Gastroenterology, 2021. PubMed 33234881.
5. Zhao Y, Dong BR, Hao Q. Cochrane review of live cultures and acute upper respiratory tract infections. 23 randomised trials, 6,950 people. Cochrane Database of Systematic Reviews, 2022. PubMed 36001877.
6. Zheng J, et al. A taxonomic note on the genus Lactobacillus: description of 23 novel genera. Taxonomic study, 261 species. International Journal of Systematic and Evolutionary Microbiology, 2020. PubMed 32293557.
7. NHS. Probiotics. nhs.uk/conditions/probiotics. Page last reviewed 24 November 2022 (review overdue).
8. Doron S, Snydman DR. Risk and safety of probiotics. Narrative review. Clinical Infectious Diseases, 2015. PubMed 25922398.
9. NHS. Sepsis. nhs.uk/conditions/sepsis. Page last reviewed 14 May 2026.
10. Brumfitt W, Hamilton-Miller JM, Ludlam H, Gooding A. Lactobacilli do not cause frequency and dysuria syndrome. Microbiological study, 142 healthy women, 26 symptomatic women and 44 bladder specimens. Lancet, 1981. PubMed 6115160.
11. Guérin F, et al. Lactobacillus delbrueckii subspecies as emerging human uropathogens in elderly patients. Case series, 48 urinary isolates, one French hospital, 2014 to 2016. Journal of Clinical Microbiology, 2025. PubMed 40265910.
12. NHS. Urinary tract infections (UTIs). nhs.uk/conditions/urinary-tract-infections-utis. Page last reviewed 11 July 2025.

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