Effect of probiotic strain, duration, and dose on preventing ICU-acquired infection: A scoping review

• Strain-specific probiotics affect ICU-acquired infection (ICU-AI) outcomes. • Lactobacillus acidophilus LA-5 showed benefits in multi-strain formulations. • ≥14-day probiotic use linked to reduced ICU-AI incidence. • Doses ≥22 × 10⁹ CFU/day were more effective in ICU settings. • Further trials are needed to explore postbiotic safety and efficacy. Intensive care unit-acquired infections (ICU-AIs) are prevalent among critically ill patients due to multiple invasive procedures. Probiotics have emerged as a potential preventive strategy to lower infection rates in ICU settings. However, studies assessing probiotic effectiveness have reported inconsistent results, suggesting that these discrepancies are due to variations in probiotic strain, intervention duration, and dosage. Despite the growing interest and the existence of several reviews, the optimal probiotic strain, duration, and dosage for ICU patients remain uncertain. This review aims to assess the impact of strain specificity, intervention duration, and dosage on the effectiveness of probiotic supplementation in preventing ICU-AIs. This scoping review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) guidelines. A comprehensive search was conducted in electronic databases for English-language interventional and observational studies published between January 2014 and September 2024. Eligible studies were those that evaluated the efficacy of probiotics in reducing ICU-AIs. Data were extracted using a standardized form that included details on strain designation, intervention duration, and dosage. Findings were synthesized descriptively using narrative text, tables, and figures. Eighteen different probiotic strains were identified. Lactobacillus acidophilus LA-5, particularly in multi-strain formulations, was commonly associated with positive outcomes. Probiotic regimens with intervention durations of 14 days or more and dosages of at least 5 × 10⁹ CFU/day demonstrated greater effectiveness in reducing ICU-AIs. Strain-specificity, intervention duration, and dosage are important factors influencing probiotic effectiveness in ICU-AI prevention. Further studies are needed to confirm the efficacy of promising strains and explore the potential of new ones. Graphical abstract illustrating a proposed mechanistic framework linking probiotic strain specificity, dosage, and intervention duration to infection-related outcomes in ICU patients. The model highlights a dose–duration threshold required to activate functional pathways influencing colonization resistance and infection risk, with differential effects observed across ICU-acquired infections.