C. difficile and Antibiotic Resistance

I am currently taking BIOL 676, Genetics of Microorganisms with Dr. Revathi Govind. During this class, we've gotten to learn a little bit about her research on Clostridium difficile. Commonly referred to as C. diff, this bacteria is gram-negative, anaerobic, spore-forming, and identified as one of the most prevalent causes of nosocomial antibiotic-associated diarrhea and colitis (Govind, et al. 2020). These spores reside within the large intestine as part of the microbiome, but are inactive in the presence of a normal gut microbiome. However, oftentimes in hospital settings, when patients are prescribed broad-spectrum antibiotics the normal gut microbes are killed off allowing the C. diff spores to germinate into vegetative C. difficile cells and begin wreaking their havoc. When the spores become viable cells, they begin to release toxins into their environment known simply as toxin A and toxin B, which target the epithelial cells of the inner intestinal wall, causing damage, and allowing for fluid leaks to accumulate in the colon (Govind et al. 2020). The image below is part of the study by Feher, Soriano, and Mensa and visually displays this process of how a healthy gut can become damaged by C. difficile. 

A review paper by Freeman et al., showed that the National Hospital Discharge Survey (representing 500 hospitals in the U.S.) found that cases of C. difficile had doubled between 1996 and 2003. If we look back on the history of antibiotics, we know that antibiotics first began to be administered around the 1930s, continuously increasing their widespread use up until the 1960s where antibiotic resistance really started to become a problem. As the perhaps overuse of antibiotics became more prevalent, the susceptible strains of bacteria were eliminated, but mutant strains of antibiotic resistant bacteria began to procure a fitness advantage, making it more and more difficult for us to control unwanted harmful bacterial strains (Freeman et al., 2010). To combat the development of C. diff without excessive use of antibiotics, Dr. Govind's lab experimented with gene regulation of the toxin producing genes in the C. diff genome. The production of RepR protein was induced into bacterial cells via transformation with a plasmid expressing the gene coding for RepR. Following the transformation, it was found that, "RepR specifically represses the tcdA and tcdR promoters when TcdR is coexpressed," (Govind et al., 2020). To simplify, they found that RepR controls the expression of the promotor region (ptcdA) for the toxin producing gene (tcdA); thus, repressing toxin production by C. diff, but only when TcdR is also coexpressed. This new method of gene regulation could prove to be a potential alternative to antibiotic use, hopefully decrease antibiotic resistance in C. difficile, and decrease hospitalization cases from the bacteria. 

Fehér, C., Soriano, A. & Mensa, J. A Review of Experimental and Off-Label Therapies for Clostridium difficile Infection. Infect Dis Ther 6, 1–35 (2017). https://doi.org/10.1007/s40121-016-0140-z

https://link.springer.com/article/10.1007/s40121-016-0140-z  

Freeman, J et al. “The changing epidemiology of Clostridium difficile infections.” Clinical microbiology reviews vol. 23,3 (Jul 2010): 529-49. doi:10.1128/CMR.00082-09

Govind, R., et al., "Bacteriophage-Mediated Toxin Gene Regulation in Clostridium difficile." Journal of Virology, 22 Dec 2020. https://doi.org/10.1128/JVI.01256-09

https://journals.asm.org/doi/10.1128/JVI.01256-09