Table 1.
Bacterial strains that affect neurotransmitter and stress hormone production- an update from Clarke et al [21]
| Molecule | Probiotic Strain, microbial metabolite | Species | Effects |
|---|---|---|---|
| Tryptophan- precursor to 5-HT | Bifidobacterium infantis | Rats | Aids in combating psychiatric disorders such as depression [84] |
| Lactobacillus johnsonii | In vitro model | Reduces serum kynurenine concentrations and IDO activity in vitro in HT-29 colonic cells, which prevents the breakdown of tryptophan [138] | |
| Serotonin | Lactococcus lactis subsp. Cremoris (MG 1363), Lactococcus lactis subsp. Lactis (IL 1403), Lactobacillus plantarum (FI8595), Streptococcus thermophilus (NCFB2392), Eschericchia coli K-12, Morganella morganii (NCIMB, 10466), Klebisella pneumoniae (NCIMB, 673), Hafnia alvei (NCIMB, 11999) | In vitro model | Produce serotonin [47, 139] |
| Butyrate and acetate produced by bacteria | Mice | Induce serotonin synthesis in a dose-dependent manner by regulating the gene Tph1 that synthesizes serotonin [68] | |
| Dopamine | Bacillus cereaus, Bacillus mycoides, Bacillus subtilis, Proteus vulgaris, Serratia marcescens, S. aureus, E.col, E.coli K-12, Morganella morganii (NCIMB, 10466), Klebisella pneumoniae (NCIMB, 673), Hafnia alvei (NCIMB, 11999) | In vitro model | Produce dopamine [140–142] |
| GABA | Lactobacillus rhamnosus (JB-1) | Mice | Regulates GABA receptor expression and reduced stress-induced corticosterone, anxiety and depression [143] |
| Bifidobacterium dentium DPC6333, Bifidobacterium dentium NCFB2243, B. infantis UCC35624, Bifidobacterium adolescentis DPC6044, Lactobacillus brevis DPC6108, Bacillus mycoides, Bacillus subtiles, Proteus vulgaris, Lactobacillus rhamnosus YS9 | Humans | Lactobacillus brevis DPC6108 was the most effective at producing GABA [8]. | |
| Cortisol | Lactobacillus helveticus R0052; Bacteroidetes longum R0175 | Humans | Reduce urinary free cortisol output [133, 144] |
| Noradrenaline | B. mycoides, B. subtilis, P. vulgaris, S. marescens, E. coli K-12 | In vitro chromatography | Regulates motility and secretions in the ENS. Elevated levels due to acute stress can cause the growth of pathogenic E. coli [140]. |