Probiotics as a Barrier Against Salmonella enterica and Escherichia coli in Contaminated Rice-Protein-Based Infant Formulas

Background/Aims: The presence of pathogens such as Salmonella enterica and Escherichia coli in infant formulas, even at concentrations below the detection threshold, poses a health risk. Probiotics have been proposed as a strategy to limit pathogen proliferation. This study evaluated two probiotic strains (Lacticaseibacillus rhamnosus HN001 and Bifidobacterium longum subsp. infantis IM-1) to inhibit the growth of these pathogens under simulated conditions. Methods: Assays were conducted using reconstituted infant formula supplemented or not with the probiotics combination and challenged with E. coli or Salmonella enterica at low inoculum levels (1 or 10 CFU/10 g). A total of 112 samples were analyzed across eight trials, with two time points (T0h and T18h). Microbial composition was characterized by sequencing the V4 region of the 16S rRNA gene followed by bioinformatic analysis using QIIME2 and the SILVA database. Results: In the absence of probiotics, E. coli and Salmonella enterica showed a marked increase in relative abundance under the tested conditions (samples C1 and C10), reaching high relative abundances at T18h. In contrast, formulas supplemented with Bifidobacterium longum subsp. infantis IM-1 and Lacticaseibacillus rhamnosus HN001 were associated with markedly lower pathogen relative abundances of both pathogens, which were either undetectable or reduced to <1% in most conditions. A concurrent increase in beneficial bacterial genera such as Lacticaseibacillus and Lactobacillus was observed, indicating competition for ecological niches and nutrients. Conclusions: The probiotics Bifidobacterium longum subsp. infantis IM-1 and Lacticaseibacillus rhamnosus HN001 exerted a reduced proliferation effect against E. coli and Salmonella enterica in infant formulas contaminated at low inoculum levels, limiting pathogen proliferation and promoting the stability of beneficial microbiota. These findings suggest that incorporating probiotics may limit pathogen proliferation in infant formulas under the experimental conditions evaluated.