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To answer the question of whether a probiotic supplement can reduce the number of infections in care home residents, to reduce antibiotic use in this vulnerable group and help curb antiobiotic drug resistance.

Why this is important

Other than vaccination and good hygiene, there are few proven ways to prevent infections in older care home residents - so they represent an important target in efforts to combat antibiotic resistance. Our study should answer the question whether or not daily probiotics prevent infections. - Professor Chris Butler, University of Oxford.

Other than vaccination and hygiene methods, there are few methods proven to prevent infection in care home residents. This group are prescribed far more antibiotics than the general population because they get more infections due to weakened immunity, close proximity living and other multiple illnesses. High antibiotic use increases the risk of resistance to antibiotics, and this resistance to antibiotics can spread within care homes and to hospitals and the community. This will become more of a problem with the UK's ageing population.

Probiotics are friendly live bacteria that may give health benefits by improving the immune system of care home residents, and reducing the spread of harmful bacteria. The study product (probiotic or matching placebo) will be taken as a capsule or sprinkled on food.

The PRINCESS trial will look at a widely available probiotic containing Lactobacillus rhamnosus and Bifidobacterium animalis to see whether it will prevent infections over 12 months.  We chose this specific probiotic due to previous research that found probiotics reduced duration of infections and enhanced immune response, including to flu vaccination. Probiotics are readily available and already used by some. However, evidence for their effectiveness in preventing infections is lacking.


We will assess total days on antibiotics for infections, immune items (including influenza vaccine response), and changes in antibiotic resistance detected in stool samples.

We will test to see if probiotics reduce antibiotic administration days by 10% or more. We will recruit 330 care home residents from about 20 care homes in Wales and England (which have around 30 residents) into an individually randomised trial of probiotic vs placebo. 

Trial participants would be expected to take a once daily dose of study product for 12 months. They will provide (optional) blood, saliva and stool samples at the start of the study, 3 and 12 months. Participants will also complete some questionnaires at these same timepoints either by themselves or with the help of someone else. A subgroup of trial participants will have additional immunological work done with regards to the routine influenza vaccine.

How could this benefit patients?

The most common reason for care home residents to be hospitalised is due to infection. Infections due to antibiotic resistance are more serious and costly in older people. Reduction in antibiotic use and antibiotic resistance could improve quality of life, save money, and help preserve the usefulness of existing antibiotics.

If positive, the study will identify a cheap food supplement intervention that may reduce infections in care home residents. If negative, then it will help inform people's decisions on whether or not to take probiotics.

Further Information:

Full project title:

A double blind placebo controlled trial to evaluate the efficacy of probiotics (Lactobacillus rhamnosus, LGG and Bifidobacterium animalis subsp. lactis, BB12) in reducing antibiotic administration for infection in care home residents.

Length of project:

July 2015 for 39 months.

Funded by:

Efficacy and Mechanism Evaluation (EME) Programme, an initiative of the Medical Research Council and the National Institute for Health Research.

External collaborators:

  • Cardiff University
  • Public Health Wales
  • University of Southampton
  • South East Wales Trials Unit

This study is coordinated by the University of Oxford's Primary Care Clinical Trials Unit.