Intelligent Living

Antibiotics that kill gut bacteria also stop new brain cells growing

Antibiotics used to kill gut bacteria also hinder the growth of new brain cells in the hippocampus, a part of the brain associated with memory, reports a study in mice published on May 19th, 2016 in Cell Reports.

Bacteria are living organisms existing as single cells. They are everywhere and most don’t cause any harm, and in some cases may be beneficial. One bacteria, Lactobacillus, for example, lives in the intestine and helps digest food.

There are over 100 trillion bacteria in your gut, some good some not so good, some big and some small. These bacteria have an impact on your health.

Good and bad bacteria diagram
Credit: rob3000 / Fotolia


The harmful ones can cause illness by invading the human body, multiplying, and interfering with normal bodily processes. Antibiotics are effective against bacteria because they work to kill these living organisms by stopping their growth and reproduction.

262 million prescriptions are written for antibiotics in 2011 in the US alone, an estimated 30% of these were inappropriate.

Scientists from the Max-Delbrueck-Center for Molecular Medicine in Berlin, Germany, found that prolonged use of antibiotics decreases neurogenesis and cognitive function. The researchers found that mice who lost their healthy gut bacteria performed worse on the memory tests.

Researchers also uncovered a clue to why, Ly6Chi monocytes, a type of white blood cell that seems to act as a correlator between the brain, the immune system, and the gut.

“Antibiotics, though remarkably useful, can also cause certain adverse effects. We detected that treatment of adult mice with antibiotics decreases hippocampal neurogenesis and memory retention. Reconstitution with normal gut flora (SPF) did not completely reverse the deficits in neurogenesis unless the mice also had access to a running wheel or received probiotics. In parallel to an increase in neurogenesis and memory retention, both SPF-reconstituted mice that ran and mice supplemented with probiotics exhibited higher numbers of Ly6Chi monocytes in the brain than antibiotic-treated mice. Elimination of Ly6Chi monocytes by antibody depletion or the use of knockout mice resulted in decreased neurogenesis, whereas adoptive transfer of Ly6Chi monocytes rescued neurogenesis after antibiotic treatment. We propose that the rescue of neurogenesis and behaviour deficits in antibiotic-treated mice by exercise and probiotics is partially mediated by Ly6Chi monocytes.”

Luckily, the adverse side effects of the antibiotics could be reversed. Mice who received probiotics or who exercised on a wheel after receiving antibiotics regained memory and neurogenesis. “The magnitude of the action of probiotics on Ly6Chi cells, neurogenesis, and cognition impressed me,” says senior author Susanne Asu Wolf. “For us, it was impressive to find these Ly6Chi cells that travel from the periphery to the brain, and if there’s something wrong in the microbiome, Ly6Chi acts as a communicating cell,” says Wolf.

Antibiotic overuse has caused certain bacteria to become resistant to even the most powerful antibiotics available today. Antibiotic resistance is a widespread problem, and one that the CDC calls “one of the world’s most pressing public health problems.”

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