The aim of this study is to explore the effects of probiotics in individuals with a clinically relevant depression on psychiatric symptoms and cognition, inflammatory parameters, as well as gene-expression. The study is conducted as a placebo-controlled, randomized, double-blind, prospective, monocentric clinical study, with a two-arm parallel group design. Individuals in the intervention group receive the multispecies probiotics "Omnibiotics Stress Repair" in addition to vitamin B7, while individuals in the control group receive "Placebo" in addition to vitamin B7.

The study takes places at the Medical University of Graz, Department of Psychiatry and Psychotherapeutic Medicine. Individuals that start inpatient treatment at the ward in the first floor of the Department because of a major depressive episode are eligible. After inclusion into the study, the participants are asked to fill in different self-rating questionnaires (Becks-Depression Inventory-II BDI-II, Symptom Checklist-90-Revised SCL-90-R, Manie-Selbstbeurteilungsskala german adaptation of Self-Report manic inventory (SRMI) - MSS, food frequency questionnaire). General data are explored routinely, as well as a diagnostic interview (MINI - mini international neuropsychiatric interview, German version 5.0) is performed during the stay at the hospital. Participants are asked to provide a stool probe as soon as possible.

At the day after admission, fasting blood is taken (100ml). Routine parameters are further analyzed at the local laboratory, while the rest is stored at -80 degree for later analyzes. Afterwards a cognitive test-battery is performed to measure verbal learning and memory, information processing speed, cognitive flexibility and working memory capacity.

After one week a further stool probe is taken, to measure possible changes in dietary habits due to the stay at the hospital. Antidepressive treatment at the hospital is continued as treatment as usual.

At the end participants go through a similar cognitive test battery as at the beginning and are asked to fill in the same self-rating questionnaires. If participants are discharged before day 28 they are given their own preparation and instructed to take it at home in the exact same manner. An outpatient appointment at the end of the preparation intake is arranged to collect the fasting blood and stool sample and to perform the cognitive assessment.

Inclusion Criteria:

• diagnosis of mood (affective) disorders (ICD 10 F3xx)
• or neurotic, stress-related and somatoform disorders (ICD 10 F4xx),
• inpatient treatment at the ward in the first floor of the Department of Psychiatry and Psychotherapeutic Medicine in Graz
• written informed consent

Exclusion Criteria:

• acute suicidality and potential dangers for themselves or other persons
• intake of antibiotics during the last month
• intake of food supplement with probiotic cultures or butyrate during the last year
• persons who are incapable of giving consent
• dementia (Mini Mental Status Examination ≤ 20)
• mental retardation
• misuse of laxatives and diuretics
• acute or chronical gastrointestinal infection or diseases
• pregnancy or breastfeeding period
• acute tumor or autoimmune diseases
• organic brain/mental disorders
• active drug or alcohol abuse