By Abbie Davis, MSc Candidate and TMED 801 Student
On Thursday, September 22nd our class, Profession of Medicine (TMED 801), was enthralled by Dr. Prameet Sheth’s medical grand rounds (MGRs) presentation. Dr. Sheth highlighted the roles of our bodies' bacterial communities (microbiota) and their genomes (microbiome) and his group’s work on a bacterial-derived protein that has the potential to translate into the treatment of humans with antibiotic-resistant bacterial infections.
It is widely recognized that the “good bacteria” in all our bodies play a role in competing with the disease-causing bacteria, and this balance is critical to human health.1 There are so many bacteria in your gut right now that experts do not even know what exactly the microbiome is made of. Clostridiodes difficle (C. diff) is just one of these disease-causing bacteria that can cause problems from diarrhea and intestinal inflammation to whole-body infection (sepsis).1 Dr. Sheth mentioned that carrying C. diff is not enough to cause health disturbances, in fact, the asymptomatic establishment of C. diff colonies has been seen in 3–5% of healthy adults.2 Rather, the toxins (Toxin A and B) C. diff produces are the main culprits, which change the cell membrane, causing cell rounding and ultimately death.3
The key cause of C. diff disease is antibiotics, which disturb the balance of good-to-bad microbes. Infection is very difficult to treat, and reoccurrence of the disease is strikingly common (25-30%), which is largely owing to the spores, which provide a stable coating around the bacteria that can allow it to live for months or even years in even the harshest environments.4 A treatment called fecal microbiota transplantation has disease resolution rates of 85%–90% after just one treatment.4,5 Fecal transplants, as Dr. Sheth describes, “re-poop-ulate” the microbiota back to its natural state. However, there are two major limitations. The first involves the strict guidelines for fecal donors, who must pass a series of blood and stool tests6 in addition to not being able to travel. It is not a surprise that many donors fail this stringent screening.
To overcome these limitations, a brilliant paper aimed to administer a sterile fecal filtrate, which was described by Dr. Sheth as a “bacteria cocktail”. This led to the development of a defined microbial community that is now called SER-109.7 Despite the obvious efficacy of both fecal transplantations and SER-109, there is still a second limitation to these treatments; an unknown mechanism.
Cue doctor Sheth and his lab, who have been working tirelessly on the mechanism of a bacteria-derived protein called High-temperature Requirement A protein (HTRA-1). Dr. Sheth created a microbiota cocktail consisting of 18 bacterial members and measured their ability to preserve mouse weight, reduce cell rounding, and decrease toxin levels. Of the 18, four were able to protect the mouse against Toxins A and B, and Parabacteroides distasonis was selected as the best target. Following a series of tests, Dr. Sheth determined that the bacteria was releasing a protein that was able to break down the toxin. Therefore, he separated the proteins and using mass spectroscopy and functional prediction techniques, Dr. Sheth was able to narrow down the protein to 9 candidates. One of these candidates, HTRA-1, was put into Escherichia coli, which reproduces at a much greater rate than Parabacteroides distasonis. Ultimately, Dr. Sheth found that HTRA-1 was able to break down more toxins with increased amounts, and that cell rounding was decreased. HTRA-1 was effective in both in virto and in vivo models. Further, HTRA-1 is a post-translational protein; therefore, this treatment target would not put the selective pressure on bacteria that results in resistance.
Dr. Sheth described the limitations of his research, which involved the use of a mouse model. The course of the disease is much more aggressive in mice and Dr. Sheth was not confident that the oral administration of the protein would withstand the human stomach. Despite this, to our best knowledge, Dr. Sheth and his group’s research was the first to show a mechanism by which the microbiota can restore and protect against C. diff. We are excited to see what is to come of the remaining 8 proteins that need to be investigated.
Following MGRs the TMED 801 class discussed with Dr. Sheth his work in the lab and as a medical microbiologist. A large area of discussion was the overuse of antibiotics for various treatments; it was reassuring to hear this issue is being combatted by medical microbiologists like Dr. Sheth, who ensure doctors are properly prescribing antibiotics. We also discussed Dr. Sheth's diverse background, from education to his time in the industry, and now, in academia. Dr. Sheth's key message to TMED students was “Don’t be afraid to make mistakes”.
Thank you, Dr. Sheth, for the engaging lecture and discussion.
References:
1. Sehgal K, Khanna S. Gut microbiome and Clostridioides difficile infection: a closer look at the microscopic interface. Ther Adv Gastroenterol. 2021;14:1756284821994736. doi:10.1177/1756284821994736
2. Sheth PM, Douchant K, Uyanwune Y, et al. Evidence of transmission of Clostridium difficile in asymptomatic patients following admission screening in a tertiary care hospital. PLOS ONE. 2019;14(2):e0207138. doi:10.1371/journal.pone.0207138
3. Di Bella S, Ascenzi P, Siarakas S, Petrosillo N, di Masi A. Clostridium difficile Toxins A and B: Insights into Pathogenic Properties and Extraintestinal Effects. Toxins. 2016;8(5):134. doi:10.3390/toxins8050134
4. van Nood E, Vrieze A, Nieuwdorp M, et al. Duodenal Infusion of Donor Feces for Recurrent Clostridium difficile. N Engl J Med. 2013;368(5):407-415. doi:10.1056/NEJMoa1205037
5. Ott SJ, Waetzig GH, Rehman A, et al. Efficacy of Sterile Fecal Filtrate Transfer for Treating Patients With Clostridium difficile Infection. Gastroenterology. 2017;152(4):799-811.e7. doi:10.1053/j.gastro.2016.11.010
6. Bibbò S, Settanni CR, Porcari S, et al. Fecal Microbiota Transplantation: Screening and Selection to Choose the Optimal Donor. J Clin Med. 2020;9(6):1757. doi:10.3390/jcm9061757
7. McGovern BH, Ford CB, Henn MR, et al. SER-109, an Investigational Microbiome Drug to Reduce Recurrence After Clostridioides difficile Infection: Lessons Learned From a Phase 2 Trial. Clin Infect Dis. 2021;72(12):2132-2140. doi:10.1093/cid/ciaa387