Conference Coverage

Early evidence shows that surgery can alter gut microbiome



– Surgery appears to stimulate abrupt changes in both the skin and gut microbiome, which in some patients may increase the risk of surgical site infections and anastomotic leaks. With that knowledge, researchers are exploring the very first steps toward a presurgical microbiome optimization protocol, Heidi Nelson, MD, FACS, said at the annual clinical congress of the American College of Surgeons.

It’s very early in the journey, said Dr. Nelson, the Fred C. Andersen Professor of Surgery at Mayo Clinic, Rochester. Minn. And it won’t be a straightforward path: The human microbiome appears to be nearly as individually unique as the human fingerprint, so presurgical protocols might have to be individually tailored to each patient.

Dr. Nelson comoderated a session exploring this topic with John Alverdy, MD, FACS, of the University of Chicago. The panel discussed human and animal studies suggesting that the stress of surgery, when combined with subclinical ischemia and any baseline physiologic stress (chronic illness or radiation, for example) can cause some commensals to begin producing collagenase – a change that endangers even surgically sound anastomoses.

Dr. Ben Shogan, a colorectal surgeon at the University of Chicago

Dr. Ben Shogan

Abdominal surgery seems to be a tipping point for changes in some Enterococcus species, causing them to express a collagen-destroying phenotype, said Ben Shogan, MD. He has completed a series of animal studies, capped with some human data, which pinpointed a strong association of these altered forms of normal microflora with anastomotic leaks.

“It’s well known that bacteria can change their function in response to host stress,” said Dr. Shogan, a colorectal surgeon at the University of Chicago. “They recognize these factors and change their entire function. In our work, we found that Enterococcus began to express a tissue-destroying phenotype in response to subclinical ischemia related to surgery.”

The pathogenic flip doesn’t occur unless there are a couple of predisposing factors, he theorized. “There have to be multiple stresses involved. These could include smoking, steroids, obesity, and prior exposure to radiation – all things that we commonly see in our colorectal surgery patients. But when the right situation developed, we can see a proliferation of collagen-destroying bacteria that predispose to leaks.”

The skin microbiome is altered as well, with areas around abdominal incisions beginning to express gut flora, which increase the risk of a surgical site infection, said Andrew Yeh, MD, a general surgery resident at the University of Pittsburgh.

He presented data on 28 colorectal surgery patients, detailing perioperative changes in the chest and abdominal skin microbiome. All of the subjects were adults undergoing colon resection who had not been on any antibiotics at least 1 month before surgery. Skin sampling was performed before and after opening, with additional postoperative skin samples taken daily while the patient was in the hospital recovering. Dr. Yeh had DNA/RNA data on 431 samples taken from this group.

Dr. Neil Hyman, professor of surgery at the University of Chicago

Dr. Neil Hyman

Preoperatively, the species diversity of the skin microbiome was similar on both sites. On the day of surgery, diversity in both sites decreased, probably because of the presurgical antiseptic shower routine employed. On postop day 1 and 2, the chest microbiome recovered its diversity, while the abdominal population stayed suppressed. By postop day 3, however, the abdominal microbiome had bloomed, exceeding both its original population and that of the chest skin.

“We saw increases in Staphylococcus and Bacteroides on the skin – normally part of the gut microflora – in relative abundance, while Corynebacterium, a normal constituent of the skin microbiome, had decreased.”

These are all very early observations, though, and the surgical community is nowhere near being able to make any specific presurgical recommendations to optimize the microbiome, or postsurgical recommendations to manage it, said Neil Hyman, MD, FACS, professor of surgery at the University of Chicago.

While it does appear that good bacteria “gone bad” are associated with anastomotic leaks, he agreed that the right constellation of factors has to be in place for this to happen, including “the right bacteria [Enterococcus], the right virulence genes [collagenase], the right activating cures [long operation, blood loss], and the wrong microbiome [altered by smoking, chemotherapy, radiation, or other chronic stressors].”

“I think it’s safe to say that developing collagenase-producing bacteria at an anastomosis site is a bad thing, but the individual genetic makeup of every patient makes any one-size-fits-all protocol approach to treatment really problematic,” Dr. Hyman said.

None of the presenters had any financial disclosures.

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