Virulence Factors of Bacterial and Viral Pathogens PDF

29/04/2021 Virulence Factors of Bacterial and Viral Pathogens | Microbiology Microbiology Microbial Mechanisms of Pathogenicity Virulence Factors of Bacterial and Viral Pathogens https://courses.lumenlearnin...

29/04/2021 Virulence Factors of Bacterial and Viral Pathogens | Microbiology Microbiology Microbial Mechanisms of Pathogenicity Virulence Factors of Bacterial and Viral Pathogens https://courses.lumenlearning.com/microbiology/chapter/virulence-factors-of-bacterial-a… 1/29 29/04/2021 Virulence Factors of Bacterial and Viral Pathogens | Microbiology LEARNING OBJECTIVES Explain how virulence factors contribute to signs and symptoms of infectious disease Di erentiate between endotoxins and exotoxins Describe and di erentiate between various types of exotoxins Describe the mechanisms viruses use for adhesion and antigenic variation In the previous section, we explained that some pathogens are more virulent than others. This is due to the unique virulence factors produced by individual pathogens, which determine the extent and severity of disease they may cause. A pathogen’s virulence factors are encoded by genes that can be identi ed using molecular Koch’s postulates. When genes encoding virulence factors are inactivated, virulence in the pathogen is diminished. In this section, we examine various types and speci c examples of virulence factors and how they contribute to each step of pathogenesis. Virulence Factors for Adhesion As discussed in the previous section, the rst two steps in pathogenesis are exposure and adhesion. Recall that an adhesin is a protein or glycoprotein found on the surface of a pathogen that attaches to receptors on the host cell. Adhesins are found on bacterial, viral, fungal, and protozoan pathogens. One example of a bacterial adhesin is type 1 mbrial adhesin, a molecule found on the tips of mbriae of enterotoxigenic E. coli (ETEC). Recall that mbriae are hairlike protein bristles on the cell surface. Type 1 mbrial adhesin allows the mbriae of ETEC cells to attach to the mannose glycans expressed on intestinal epithelial cells. Table 1 lists common adhesins found in some of the pathogens we have discussed or will be seeing later in this chapter. https://courses.lumenlearning.com/microbiology/chapter/virulence-factors-of-bacterial-a… 2/29 29/04/2021 Virulence Factors of Bacterial and Viral Pathogens | Microbiology Table 1. Some Bacterial Adhesins and Their Host Attachment Sites Attachment Pathogen Disease Adhesin Site Respiratory Streptococcus Strep Protein F epithelial pyogenes throat cells Streptococcus Dental Adhesin P1 Teeth mutans caries Urethral Neisseria Gonorrhea Type IV pili epithelial gonorrhoeae cells Intestinal Enterotoxigenic E. Traveler’s Type 1 mbriae epithelial coli (ETEC) diarrhea cells N- Intestinal Vibrio cholerae Cholera methylphenylalanine epithelial pili cells CLINICAL FOCUS: PANKAJ, PART 3 This example continues Pankaj’s story that started in Characteristics of Infectious Disease and How Pathogens Cause Disease. The presence of bacteria in Pankaj’s blood is a sign of infection, since blood is normally sterile. There is no indication that the bacteria entered the blood through an injury. Instead, it appears the portal of entry was the gastrointestinal route. Based on Pankaj’s symptoms, the results of his blood test, and the fact that Pankaj was the only one in the family to partake of the hot dogs, the physician suspects that Pankaj is su ering from a case of listeriosis. 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. Once ingested, these bacteria invade intestinal epithelial cells and translocate to the liver, where they grow inside hepatic cells. Listeriosis is fatal in about one in ve normal healthy people, https://courses.lumenlearning.com/microbiology/chapter/virulence-factors-of-bacterial-a… 3/29 29/04/2021 Virulence Factors of Bacterial and Viral Pathogens | Microbiology and mortality rates are slightly higher in patients with pre- existing conditions that weaken the immune response. A cluster of virulence genes encoded on a pathogenicity island is responsible for the pathogenicity of L. monocytogenes. These genes are regulated by a transcriptional factor known as peptide chain release factor 1 (PrfA). 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. A second gene regulated by PrfA is actA, which encodes for a surface protein known as actin assembly-inducing protein (ActA). ActA is expressed on the surface of Listeria and polymerizes host actin. This enables the bacterium to produce actin tails, move around the cell’s cytoplasm, and spread from cell to cell without exiting into the extracellular compartment. Pankaj’s condition has begun to worsen. He is now experiencing a sti neck and hemiparesis (weakness of one side of the body). Concerned that the infection is spreading, the physician decides to conduct additional tests to determine what is causing these new symptoms. What kind of pathogen causes listeriosis, and what virulence factors contribute to the signs and symptoms Pankaj is experiencing? Is it likely that the infection will spread from Pankaj’s blood? If so, how might this explain his new symptoms? We’ll conclude Pankaj’s example later on this page. Bacterial Exoenzymes and Toxins as Virulence Factors After exposure and adhesion, the next step in pathogenesis is invasion, which can involve enzymes and toxins. Many pathogens achieve invasion by entering the bloodstream, an e ective means of dissemination because blood vessels pass close to every cell in the body. The downside of this mechanism of dispersal is that the blood also includes numerous elements of the immune system. Various terms https://courses.lumenlearning.com/microbiology/chapter/virulence-factors-of-bacterial-a… 4/29 29/04/2021 Virulence Factors of Bacterial and Viral Pathogens | Microbiology ending in –emia are used to describe the presence of pathogens in the bloodstream. The presence of bacteria in blood is called bacteremia. Bacteremia involving pyogens (pus-forming bacteria) is called pyemia. When viruses are found in the blood, it is called viremia. The term toxemia describes the condition when toxins are found in the blood. If bacteria are both present and multiplying in the blood, this condition is called septicemia. Patients with septicemia are described as septic, which can lead to shock, a life-threatening decrease in blood pressure (systolic pressure