Salmonella enterica serovar Typhimurium bacteria (S. Typhimurium) often cause gastroenteritis in humans, an inflammation of the intestinal lining. The bacteria live in the gut and can infect the epithelial cells that line its surface. Many studies have shown that salmonella uses a "run-and-tumble" method for short periods of swimming (runs) interrupted by falls when they accidentally change direction, but how they move in the intestines is not well understood .
The National Institutes of Health scientists and their colleagues believe a S. Typhimurium protein, McpC (methyl-accepting chemotaxis protein C), which allows bacteria to swim just when they are ready to infect cells. This new study, published in Nature communication, describes S. Typhimurium movement and shows that McpC is required for the bacteria to invade surface epithelial cells in the intestine.
The study's authors suggest that McpC is a potential target for the development of new antibacterial treatments to hinder the ability of S. Typhimurium for infecting intestinal epithelial cells and colonizing the intestine. Scientists from the National Institute of Allergy and Infectious Diseases at Rocky Mountain Laboratories in Hamilton, Montana led the study. Staff included groups from the University of Texas A&M locations at College Station and Kingsville.
S. Typhimurium uses flagella – long, whip-like protrusions – to move through fluids. When the flagella rotate counterclockwise, they form a rotating bundle behind the bacteria and propel them forward. However, the flagella often alternate rotation from counterclockwise to clockwise, destroying the bundle and causing the bacteria to fall and change direction. Use special microscopes and cameras to observe live S. Typhimurium, the scientists found that bacteria that grew in conditions that activate their invasive behavior swam in longer straight runs because the flagella did not rotate from counterclockwise to clockwise. Bacteria lacking McpC still displayed the "run-and-tumble" method of swimming under these conditions and had an invasive defect in a calf intestinal model, suggesting that straight swimming is important for efficient invasion of intestinal epithelial cells.
The researchers hypothesize that controlled smooth swimming could be a widely used strategy for bacterial infections. Similar smooth swimming behavior can be observed in unrelated enteric bacteria such as Vibriowhich can lead to infections when eating undercooked seafood. These results could influence the development of novel antibiotics.
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