![]() One of the genes regulated by PrfA is hyl, which encodes a toxin known as listeriolysin O (LLO), which allows the bacterium to escape vacuoles upon entry into a host cell. ![]() These genes are regulated by a transcriptional factor known as peptide chain release factor 1 (PrfA). A cluster of virulence genes encoded on a pathogenicity island is responsible for the pathogenicity of L. Listeriosis is fatal in about one in five normal healthy people, and mortality rates are slightly higher in patients with pre-existing conditions that weaken the immune response. Once ingested, these bacteria invade intestinal epithelial cells and translocate to the liver, where they grow inside hepatic cells. Listeria monocytogenes, the facultative intracellular pathogen that causes listeriosis, is a common contaminant in ready-to-eat foods such as lunch meats and dairy products. Based on Michael’s symptoms, the results of his blood test, and the fact that Michael was the only one in the family to partake of the hot dogs, the physician suspects that Michael is suffering from a case of listeriosis. Instead, it appears the portal of entry was the gastrointestinal route. There is no indication that the bacteria entered the blood through an injury. The presence of bacteria in Michael’s blood is a sign of infection, since blood is normally sterile. Table 15.7 lists common adhesins found in some of the pathogens we have discussed or will be seeing later in this chapter. Type 1 fimbrial adhesin allows the fimbriae of ETEC cells to attach to the mannose glycans expressed on intestinal epithelial cells. Recall that fimbriae are hairlike protein bristles on the cell surface. One example of a bacterial adhesin is type 1 fimbrial adhesin, a molecule found on the tips of fimbriae of enterotoxigenic E. Adhesins are found on bacterial, viral, fungal, and protozoan pathogens. Recall that an adhesin is a protein or glycoprotein found on the surface of a pathogen that attaches to receptors on the host cell. Virulence Factors for AdhesionĪs discussed in the previous section, the first two steps in pathogenesis are exposure and adhesion. In this section, we examine various types and specific examples of virulence factors and how they contribute to each step of pathogenesis. When genes encoding virulence factors are inactivated, virulence in the pathogen is diminished. A pathogen’s virulence factors are encoded by genes that can be identified using molecular Koch’s postulates. This is due to the unique virulence factor s produced by individual pathogens, which determine the extent and severity of disease they may cause. In the previous section, we explained that some pathogens are more virulent than others. ![]() Describe the mechanisms viruses use for adhesion and antigenic variation.Describe and differentiate between various types of exotoxins.Differentiate between endotoxins and exotoxins.Explain how virulence factors contribute to signs and symptoms of infectious disease.By the end of this section, you will be able to: ![]()
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