A new study indicates that microbial diversity in the gut correlates closely with the severity of major depressive disorder. Compared to healthy individuals, the abundance of Bacteroids species was significantly increased in participants with moderate and severe depression, whereas Ruminococcus AND Eubacterium they were mostly depleted in participants with severe depression. The study was published in Translational psychiatry.
Depression, also known as major depressive disorder, is the most common form of mental illness. It is believed to affect more than 350 million people worldwide. The main symptoms of depression include persistent feelings of sadness, loss of interest or pleasure in activities, changes in appetite or weight, trouble sleeping, fatigue, feelings of worthlessness or guilt, difficulty concentrating or making decisions, and recurring thoughts of death or suicide. As such, it creates a huge social cost both on the individual suffering from it and on society.
New studies have led to the discovery of the microbiota-gut-brain axis, a complex network that enables communication between the diverse community of microorganisms residing in the gastrointestinal tract and the brain. Because this communication is bi-directional, researchers have looked at the links between gut microbiota composition and psychological properties, such as cognition and well-being, but also mental health.
Study author Xi Hu and his colleagues wanted to explore differences in gut microbiota composition among people with depression, but with different levels of symptoms. They noted that previous studies have used methods to identify bacterial species with limited accuracy and decided to use metagenome sequencing for this purpose.
Metagenome sequencing is a genomic technique used to analyze the genetic material, DNA or RNA, present in a complex mixture of microorganisms, such as those found in environmental samples or within a human body. Instead of focusing on the genetic material of a single organism, metagenome sequencing allows for the simultaneous analysis of the collective genetic material of an entire microbial community. Since the goal of the procedure, in this case, was to evaluate the microbial composition of the participants\’ intestines, it was used on stool samples.
Study participants were 138 people with depression of varying severity from mild to severe and 155 healthy individuals who served as controls. Depression severity was rated using the HAMD-17 scale. Participants who were pregnant or breastfeeding, had used antibiotics within one month prior to sampling, had a history of alcohol or substance abuse, or chronic somatic illnesses or other serious psychiatric disorders were excluded from the study.
Stool samples were collected at the clinical site where the study was conducted. This was done in the morning between 7am and 10am. Samples were stored in sterile tubes at 4°C, then transferred to a refrigerator at 80°C. Processing was done within 6 hours.
Results showed that, overall, at the household level, Bacteroidaceae, Lachnospiraceae, Ruminococcaceae, and Prevotellaceae were the major bacterial taxa with high abundance in all healthy participants and those with depression. At the genus level, Bacteroides, Faecalibacterium, Blautia, Prevotellaceae were the main bacterial taxa with high abundance in both groups.
Compared to the healthy control group, bacteria from the Bacteroides group were much more abundant in participants with moderate and severe depression. Faecalibacterium AND Escherichia were decreased in the group with moderate depression symptoms, while Ruminococcussand Eubacterium they were decreased only in the group with severe depression symptoms.
When enterotypes, distinct types of bacterial communities within the human gut microbiota, were examined, the results showed that an enterotype dominated by Faecalibacteriumwas more abundant in the healthy group, while two enterotypes were dominated by Bacteroids were more abundant in the group of patients with depression.
In this study, we found that the gut microbiota of patients with moderate and severe major depressive disorder was characterized by the enrichment of BacteroidetesWhile Ruminococcus AND Eubacterium were depleted in severely ill patients. Consistently, the major enterotype of the healthy controls was Faecalibacterium. Furthermore, we also identified a panel of microbial markers that can distinguish patients with major depressive disorder with different severities,\” concluded the researchers.
The study provides an important contribution to the scientific understanding of the links between gut microbiota composition and mental health. However, it should be noted that the study design does not allow for cause and effect conclusions to be drawn. Additionally, all specimens were collected from the same regional clinical center. Results on people from other regions or countries may not be the same.
The study, Gut microbiota changes reflect severity of major depressive disorder: A cross-sectional study, was written by Xi Hu, Yifan Li, Jing Wu, Hanping Zhang, Yu Huang, Xunmin Tan, Lu Wen, Xingyu Zhou, Peijun Xie , Oluwatayo Israel Olasunkanmi, Jingjing Zhou, Zuoli Sun, Min Liu, Guofu Zhang, Jian Yang, Peng Zheng and Peng Xie.
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