Roseville-based gut-health company Rebiotix has developed what it says is an objective system to measure changes in the intestine that can leave hospital patients vulnerable to deadly "C. diff" infections.

The Microbiome Health Index (MHI), announced on Monday by Rebiotix, is intended to provide the gut-microbe research community with an objective way to measure the effectiveness of experimental treatments developed for gut health.

Specifically, the MHI quantifies the relationship between four key classes of bacteria into a single metric that can identify people who have unhealthy imbalances in the microbial communities in their intestines.

Such imbalances are thought to affect the body's immune system, metabolism, digestive health and even cancer and mental health. The Food and Drug Administration has not granted formal approval to any application of gut-microbiome medicine, although drug candidates are in clinical trials.

Several companies are developing such therapies, but Rebiotix is the furthest along in the process and has generated the most positive data so far.

Separately, the FDA allows doctors to treat patients in clinic for stubborn infections of the bacterium Clostridium difficile, or C. diff, which causes bouts of serious diarrhea in many of the roughly 500,000 people per year who contract infections with it. More than 29,000 people die annually from the disease, which commonly takes root after a patient takes powerful antibiotics that wipe out the natural gut microbes that normally keep C. diff in check.

Rebiotix has already used its MHI tool in a Phase 2 clinical trial for its microbiota drug candidate RBX2660 for recurrent C. diff infection.

The trial found last year that 79 percent of 132 patients who received two doses of RBX2660 had successful results eight weeks after treatment, compared to 52 percent of patients in a historical control arm.

(Common adverse events included diarrhea, abdominal pain, flatulence and constipation.)

MHI will be used on the Phase 3 trial data, once they have been collected, and is also being used in the Phase 1 clinical trial ofRebiotix RBX7455, which is similar to RBX2660 but is administered in capsule form instead of via enema.

The raw microbes that make up both drugs are derived from human stool, which is taken from approved donors and screened for pathogens before being processed into material that the FDA considers a drug. The material is used in what's known as a fecal microbiome transplant, or FMT, in which the recipient's intestine is repopulated with a donor's microbes to fight off infection.

While such a therapy may present an "ick factor" for some observers, doctors and microbiome experts say patients suffering in the throes of long-term, treatment-resistant diarrhea from C. diff are seeking improvement and don't tend to have the same aversion as a healthy person thinking about it.

Rebiotix is a small, clinical-stage company founded with $5 million in seed funding in 2011. It is developing a drug-delivery platform to deliver live human-derived microbes into a patient's intestines using standardized screening and storage processes. Its new-drug applications have received special designations from the FDA that allow for expedited testing.

The MHI tool was developed in partnership with St. Louis-based data analytics firm BioRankings, which has expertise in microbiome data analysis as well as statistical due diligence for health-science investors.

"Our vision is for MHI to become a standard measure for microbiome research, potentially serving as a validated endpoint for clinical trials and providing both a predictive measure and actionable data," said Bill Shannon, managing partner of analytics at BioRankings, in a news release.

Rebiotix CEO Lee Jones said in a recent interview that although her company is leading the small pack of companies working on microbiome therapies today, the field is still young and market interest is likely to kick up over time as the therapies show results in trials.

"This market is at its very early infancy, and the more people involved in this space, the better it is for everyone. Then we're all generating data" and examining it, she said. "I would imagine that there is going to be a lot of competition — and I would expect that, given the opportunities in this industry."