Bacteria Culpable in Gastrointestinal Surgery Complications

Postsurgical intestinal anastomotic leaks are often the result of bacteria in the bowel that elude antibiotics, according to a new study.

Researchers at the University of Chicago (IL, USA) searched for the root cause of intestinal anastomotic leaks by resecting one centimeter of the lower colon in healthy rats, and then reconnecting the two adjoining segments. The leaks that appeared were caused apparently by the breakdown of collagen in the healing intestinal wall, and so the researchers looked for bacteria that might make enzymes capable of such collagen degradation. Then they used genetics to track the bacteria found at the surgical site; of all the bacteria, E. faecalis stood out as the dominant microbe.

They found that by the time leaks occurred, the relative abundance of E. faecalis had increased from baseline 500-fold. They also found that by degrading intestinal connective tissues such as collagen I, the bacteria succeeded in dissolving the scar tissue needed to seal the intestine during healing by creating small holes in the intestine at the anastomosis. E. faecalis also activates the enzyme matrix metalloprotease 9 (MMP9), which degrades collagen IV, another connective tissue involved in wound healing.

Two different strains of E. faecalis were identified. One of them, labeled E1, produced limited collagenase, while the more virulent E2 strain produced a great deal, and began degrading collagen much sooner. When the researchers exposed rats to each of the two strains (via enemas) soon after surgery, those that received the E2 strain all developed leaks at the surgical site within six days. No rats receiving strains that produced negligible amounts of collagenase formed a leak. The study was published on May 6, 2015, in Science Translational Medicine.

“For more than 60 years, surgeons have suspected that intestinal microbes played a causative role in leakage after intestinal surgery,” said senior study author Prof. John Alverdy, MD, of the department of surgery. “But we were never certain how much they contributed, which bacteria were involved, or how to prevent it. Identification of one of the primary microbial culprits points us toward better ways to reduce the risk.”

Postsurgical leaks are a devastating complication of gastrointestinal surgery which can develop days or even weeks after the procedure, allow the bowel's contents to spill into the abdomen and causing pain, fever, sepsis, and even death. High risk surgery, such as in the rectum, can results in leak rates of 30%, compelling surgeons to perform a temporary colostomy to stream stools directly from the intestine into an external bag. This approach protects the newly formed intestinal connection, giving it a chance to heal, but it can be distressing to patients and requires a second operation to restore intestinal continuity.

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