Multi-Criterion In Vitro Profiling of Probiotic Strains for Preliminary Gut–Skin-Axis-Oriented Candidate Prioritization

The gut-skin axis is a promising target for oral probiotics, yet strain choice is often empirical, rather than aligned to defined, skin-relevant functional readouts. Here, we performed a predefined multi-criterion in vitro screening of lactobacilli and bifidobacteria to prioritize candidate strains for gut-skin-axis-oriented development. The screening combined four complementary readouts: antagonistic activity against selected skin-associated pathobionts, targeted liquid chromatography-tandem mass spectrometry (LC-MS/MS) profiling of metabolites in cell-free supernatants (CFS), a simple surface-binding assay based on binding to polystyrene, and transepithelial electrical resistance (TEER) monitoring in Caco-2 intestinal epithelial monolayers during early monolayer maturation. Antimicrobial activity was strongly strain dependent and most pronounced against Staphylococcus aureus and Cutibacterium spp., with Lacticaseibacillus rhamnosus SCN01 and Limosilactobacillus fermentum LF160 showing the broadest inhibition profiles. Replicated metabolomics revealed distinct, reproducible extracellular signatures: lactate dominated across lactobacilli, B. breve SCN03 showed the clearest acetate increase, and L. fermentum LF160 displayed a coordinated arginine-to-ornithine/citrulline shift with high succinate. Nicotinic acid (vitamin B3) accumulated most in Lactobacillus acidophilus LA120 and B. breve SCN03, whereas pyridoxal (vitamin B6) and GABA were most enriched in L. plantarum SCN02; in the shortlisted strains, selected biogenic amines remained low in the replicated targeted panel. Functionally, L. rhamnosus SCN01 produced the strongest sustained TEER increase without detectable changes in cellular metabolic activity. Collectively, these data support a transparent, hypothesis-generating framework for preliminary in vitro prioritization of oral probiotic candidates with complementary antimicrobial, metabolic, surface-binding and epithelial-resistance-associated profiles. Further mechanistic, community-based, skin-cell, preclinical and clinical studies will be required to determine whether these in vitro profiles translate into gut-skin-axis-relevant benefits.