PRINCESS - A study to examine whether care home patients experience health benefits, such as reduced infections, from taking a daily probiotic supplement.

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.

Principal / Lead Investigator
Type of study

Randomised controlled trial (RCT)


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.

Who is the study sponsor?

University of Oxford

Does the study involve commercial partnership activity?


UKCRN portfolio number 



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

Total grant value


Amount accruing to your group

Details to follow

Start date


End date


Potential benefit to 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

Study website: https://www.princess-study.co.uk/

Study summary on University of Oxford website: http://www.phc.ox.ac.uk/research/infectious-diseases/studies/princess-probiotics-to-reduce-infections-in-care-home-residents