The human body’s microbiota — the rich community of bacteria and other microorganisms colonizing the skin and the gut — plays a crucial role in one’s ability to accept transplanted organs, a new study reveals.

The type of bacteria present in the donor and recipient, for instance, can affect the acceptance or rejection rate of a transplant.

Researchers from the University of Chicago demonstrated that treating both donor and recipient mice with antibiotics prior to the procedure upped the amount of time that skin grafts survived on the animals – a two-fold increase compared with mice that didn’t receive the medication.

The antibiotic treatments appeared to kill some kinds of bacteria, prompting the transplants to survive for a longer time. Data suggested that while some bugs induce faster rejection, those that survive antibiotics do not retain the same ability.

"The species that form the community of microbes colonizing the mice — and supposedly humans too — have different effects," said senior study author and medicine professor Dr. Maria-Luisa Alegre.

In newborn human babies, microbes from the mothers rapidly colonize their bodies, slowly increasing and maturing as the youngsters grow up. From there a distinct set of gut microbiome develops, with functions that go beyond digestion and include the immune system.

In both humans and lab animals, success rates of skin, lung and intestinal transplants — involving organs exposed to the external world — fare much worse than internal organ transplants, such as hearts and kidneys. It is hypothesized that the difference lies in that these externally exposed organs are colonized by microbiomes, while sterile internal ones aren’t.

The team treated the donor and recipient mice with antibiotics for 10 days before they performed skin transplants, which had a survival time of 53 days. In contrast, a survival period of 27 days was noted in the untreated group.

They also tested the impact of fecal microbiota transplants from the treated and untreated mice groups on germ-free mice, seeing that those getting fecal transplants from untreated mice rejected grafts sooner than those getting fecal transplants from treated mice.

They saw similar results with heart transplants, with transplants surviving longer for antibiotic-treated mice.

Based on genetic analysis of skin bacteria on antibiotic-treated mice, the total bacterial load was the same in untreated mice but with substantially fewer unique species. Alegre explained that the bacterial composition — not really the total number — made the difference.

These findings are deemed promising in producing better strategies for improved transplant results in humans. More narrow-spectrum antibiotic drugs, for instance, could target only a single bacteria triggering a rejection response.

"We have evolved to cohabit effectively with our microbes, and they are very beneficial. We need them,” reminded Alegre, encouraging good microorganism balance in the body.

The findings were published June 20 in The Journal of Clinical Investigation.

Photo: Azat Akhyarov | Flickr

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