BLIS study: a feasibility randomised controlled trial assessing compliance, acceptability and colonisation with different dosing regimens of the probiotic supplement Streptococcus salivarius K12 (Bactoblis) in adults in England.

OBJECTIVES

Streptococcus salivarius K12 (SsK12) is a bacterium used as a probiotic with some evidence for preventing acute sore throat/tonsillitis, but the optimal dosing strategy is unclear. This study aimed to evaluate two dosing regimens of SsK12 to establish (a) the prevalence and duration of colonisation with SsK12 and (b) the acceptability and feasibility of these regimens.

DESIGN

A randomised, non-blinded feasibility trial.

SETTING

Primary care in the south of England.

PARTICIPANTS

Adults with ≥2 episodes of sore throat within the 3 years before recruitment.

INTERVENTIONS

Participants were randomised to take SsK12 lozenges once weekly or daily over 14 days.

MAIN OUTCOME MEASURES

The primary outcome was the prevalence and duration of colonisation with SsK12. This was determined by real-time PCR conducted on self-taken whole-mouth swabs provided by participants at baseline and on days 2, 7, 14, 21 and 35. Secondary outcomes were the compliance and acceptability of the two SsK12 dosing regimens, based on questionnaire data.

RESULTS

53 participants were recruited (26 randomised to weekly and 27 to daily dosing) between 26 April and 5 December 2023. All swabs were returned by 65.4% (17/26) and 70.4% (19/27) of the weekly and daily groups respectively. Swabs at all timepoints from participants with PCR positives observed at baseline (two and four from the weekly and daily group, respectively) were excluded. Therefore, swabs from 23 participants in the weekly and 22 in the daily group did not have evidence of baseline colonisation and were included in the microbiology analysis. SsK12 colonisation was found in 59.1% (13/22, 95% CI 38.6% to 79.6%) of samples in both groups on day 2; in 13.6% (3/22, 95% CI 0.0% to 28.0%) and 85.7% (18/21, 95% CI 70.8% to 100.0%) of the weekly and daily groups, respectively, on day 7; in 19.1% (4/21, 95% CI 2.3% to 35.8%) and 59.1% (13/22, 95% CI 38.6% to 79.6%), respectively, on day 14; and in only one participant (weekly group) on days 21 and 35. The dosing regimen was reported as easy to follow by 85.0% (17/20, 95% CI 69.4% to 100.0%) of the weekly and 96.2% (25/26, 95% CI 88.8% to 100.0%) of the daily dosing groups.

CONCLUSIONS

SsK12 colonisation was more prevalent with daily dosing; however, colonisation was not maintained when dosing stopped. Both dosing regimens were acceptable to participants. These findings support the use of daily dosing in a future trial to evaluate the efficacy of SsK12 in preventing recurrence of sore throat/tonsillitis.

TRIAL REGISTRATION NUMBER

NCT04297878.

© Author(s) (or their employer(s)) 2026. Re-use permitted under CC BY. Published by BMJ Group.