Antimicrobial sensing and resistance in Clostridioides difficile

Clostridioides difficile is an anaerobic bacteria that is a common cause of hospital acquired infections. C. difficile infections most commonly occur when a patient has been prescribed antibiotics for a different infection. These antibiotics can disrupt the normal gut microflora, which provides C. difficile the opportunity to colonize, persist, and establish infection. One reason C. difficile can be difficult to treat is its resistance to wide variety of antimicrobials, either those that are produced by the host during infection, or antibiotics that are prescribed to a patient to help treat infection. A common host factor that is produced during infection is a protein called lysozyme, which can kill bacteria via damage to the major component of the cell wall, peptidoglycan. C. difficile has several known lysozyme resistance factors, the best studied of which is a regulatory protein called σ^V that acts to increase lysozyme resistance by increasing activity of peptidoglycan deacetylases, which make it more difficult for lysozyme to bind to the cell. RsiV is a protein that prevents σ^V from being active until it is need. In the presence of lysozyme RsiV is degraded in a series of proteolytic steps that frees σ^V, allowing it to activate the production of the peptidoglycan deacetylase PdaV. In order to survive in hash environments, bacteria must be able to sense, interpret, and respond to stressors. One common way in which bacteria can achieve this is through two-component systems (TCS). Canonical TCS’s consist of a sensor protein, called a sensor histidine kinase, and a regulatory protein called a response regulator. We have identified several TCS’s that appear to be involved in lysozyme resistance. We have also identified a network of TCS’s that respond to certain antimicrobials that inhibit peptidoglycan biosynthesis, and one of these, DraRS, confers resistance to two antimicrobials, daptomycin and bacitracin. We also identified another TCS, HexRK, which regulates 3 genes, hexSDF. We found that HexSDF is required to make a large portion of the C. difficile membrane lipids. Without these unique lipids synthesized by HexSDF, C. difficile becomes more sensitive to bacitracin and daptomycin.