5 obj331 infection

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5 obj331 infection

  1. 1. Infection-viv 1. Define infection, host, infectivity, virulence, immunogenicity, toxigenicity, symbiosis, mutualism, commensalism, and pathogenicity. (M294, M295) • Infection-direct damage of cells, interference with cellular metabolism, and rendering a cell dysfunctional because of the accumulation of pathogenic substances and toxin production • Host-by which a pathogen microorganism infects • Infectivity-ability of the pathogen to invade and multiply in the host. • Virulence-potency of a pathogen measured in terms of the number of microorganisms of µg of toxin required to kill a host. (ie. Measles virus is of low virulence; rabies virus is highly virulent) • Immunogenicity-ability of pathogens to induce an immune response. • Toxigenicity-a factor important in determining a pathogen’s degree of virulence, that is, the ability to produce disease by production of a soluble toxin. (ie.hemolysin, a product of streptococci, destroys erythrocytes). • Symbiosis-benefits only the human, no harm to the organism. • Mutualism-benefits both the human and organism. • Commensalism-benefits only the organism, no harm to the human. • Pathogenicity-benfits the organism, harms the human. (Opportunism is when benign human organisms become pathogenic because of decreased human host resistance).2. List five innate host defense mechanisms that will impact the host’s ability toprevent invasion by a pathogen. (M295) • The first lines of defense against infectious microorganism are external barriers: o 1) skin o 2) mucous membranes o 3) genitourinary tract o 4) digestive tract o 5) respiratory tract3. Describe the concept of host-microorganism interaction by using the definition ofsymbiosis, mutualism, commensalism, and pathogenicity to provide examples ofinteractions. (M295) • Symbiotic relationships occur when there is benefit to the human and no harm to the organism, such as some gut bacteria, as they help digest food. • Mutualistic relationships occur when there is benefit to both the human and the organism, as in normal flora of the skin, gut, mouth. Page 1 of 5
  2. 2. • Commensalistic relationships occur when the organism benefits, and there is no harm to the human. (no examples in McCance). • Pathogenicity arises in situations where the organism benefits, the human is harmed, an example would be a tape worm living in the human gut. Term To Host To Bact Symbiotic Benefit no harm Mutualistic Benefit Benefit Commensalistic No Harm Benefit Pathogenisity Harmed Benefit4. Describe 6 microbial factors that improve the chance of a pathogen establishingan infection in a host. (M296-299) • Antigenic variation allows the pathogen to change appearance by altering antigens, thus challenging the specificity of the immune system. This is accomplished by mutation, recombination, and gene switching. Antigenic variation can occur during the course of infection, and spread of infection through the environment. 1. Antigenic drift is the change that results from mutations (ie. Flu viruses) 2. Antigenic shifts are major changes in antigenicity that occur from recombination of genomes (can result in pandemics). 3. Gene switching is used to avoid immune response. Involves pathogens switching on and off surface proteins to allude immune system. 4. Microorganisms can produce thick capsules of carbohydrate or protein that are antiphagocytic preventing opsonization & phagocytosis. 5. Exotoxin production - damage the plasma membrane of host cells or prevent phagocytosis. 6. Endotoxins production - activate inflammatory response and produce fever.5. Identify eight classes of infectious organisms, their individual site of reproduction,and provide an example of an organism that fits within the class. (M295) Class of pathogen Site of reproduction ExampleVirus Intracellular PoliomyelitisChlamydia Intracellular TrachomaRickettsiae Intracellular Rocky Mountain Spotted FeverMycoplasma Extracellular Mycoplasm pneumonia Page 2 of 5
  3. 3. Bacteria Skin, Staphylococcal wound infection mucous membranes, Cholera Intracellular, Streptococcal pneumonia Extracellular TuberculosisFungi Skin, Tinea pedis mucous membranes, Candida Intracellular, Sporotrichosis Extracellular HistoplasmosisProtozoa Mucosal Giardiasis Extracellular Sleeping sicknessHelminths Intracellular Trichinosis Extracellular Filariasis6. Describe the process used by bacteria to establish an infection in a susceptiblehost. Make sure to include a discussion of the role of endotoxins, exotoxins, and therole of proteases that digest IgA.Bacterial survival and growth depend on effectiveness of the body’s defense mechanismsand on the bacterium’s ability to resist those defenses and obtain nutrients and multiply.a) Bacteria must have Iron to multiply, and some express siderophores (iron receptors)that acquire iron from iron binding proteins (i.e., lactoferrin, transferrin, and hemoglobin)b) Some pathogens have ways of preventing destruction by the inflammatory andimmune systems. They produce thick capsules of carbohydrate or proteins that areantiphagocytic, example is the thick polysaccharids covering of the pneumococcus andwaxy capsule surrounding tubercle baccilus.c) Some pathogens have developed the ability to proliferate at rate that surpass thedevelopment of a protective response.d) Other bacteria survive and proliferate in the body by producing Exotoxins andendotoxins that injure cells and tissue.e) Exotoxins are proteins released during bacterial growth. Can damage cell membranes, activate second messengers, and inhibit protein synthesis (available vaccines for this are: tetanus)f) Endotoxins: are libopolysacharids (LPS) -contain cell walls of gram-negative bacteriaand released during lysis (destruction)7. Describe the process used by viruses in establishing an infection in a susceptiblehost. Make sure to include a discussion of the cellular effects of viruses. Page 3 of 5
  4. 4. Viruses are intracellular parasites that take over the genetic and metabolic machinery ofthe host cells and use them for their own survival and replication. Viruses contain geneticinformation in either DNA or RNA. Infection with viruses requires it to bind a specificreceptor on the plasma membrane of the host cell. Viral replication depend on absorption,penetration, uncoating , replication , assembly and release of new viruses.Once inside the host cell, virions have many harmful effects which includes thefollowing:a) Inhibition of the host cell DNA, RNA, or protein synthesisb) Disruption of lysosomal membranes, resulting in release of digestive lysosomalenzymes that can kill the cellc) Promotion of infected, adjacent host cells, thereby producing multinucleated giantcelld) Alteration of antigenic properties, or identity of the host cell, causing the host’simmune system to attack the cell as if it were foreign e) Transformation of host cells into cancerous cellsf) Promotion of secondary bacterial infection in tissues or organs damage by virusesu8. Describe the process used by fungi in establishing an infection in a susceptiblehost. Fungi are large microorganisms with thick walls that grow as either single-celled yeast ormulticelled molds. Same fungi can exist in either form and are called Dimorphic. The cell wall ofthe fungi is rigid and multilayered. The cell wall is composed of polysaccharides differentfrom peptidoglycans of the bacteria.a) The lack of peptidoglycans allows fungi to resist the action of bacterial cell wall inhibitors suchas Penicillin and cephalosporin.b) The fungi can produce infection by adopting the host environment. Fungi can colonize the skincan digest keratin; other fungi can grow with wide temperature variations in low oxygenenvironment.c) Fungi has capacity to suppress the host immune defenses, lymphocytes and phagocytes areimportant in controlling fungi, low white blood cell counts promotes fungal infection.9. Describe both local and systemic clinical manifestations of infection and relate tothe process of inflammation. Clinical manifestations of infectious disease vary, depending on the pathogen, the organaffected and the severity. The effect of the infection may be acute or chronic, related to immuneresponses, or consequence of bacterial toxins. Manifestation can arise directly from the infectingmicroorganism or its products; however the majority of manifestation result from the host’sinflammatory and immune responses. Page 4 of 5
  5. 5. Infectious disease typically began with the nonspecific or general symptoms of fatigue, malaise,weakness, and loss of concentration. General aching and loss of appetite are commoncomplications. However, the hallmark of most infectious disease is Fever.Body temperature is regulated by nervous system feedback to the hypothalamus, which functionsas a central thermostat. A large number of agents ( pyrogens) can produce fever. In currentclassification those pyrogens derived outside the host are termed Exogenous Pyrogens and thoseproduced by the host are termed Endogenous Pyrogens. There is little evidence that exogenouspyrogens cause fever directly.Available data favors an indirect effect of such pyrogens on the hypothalamus that is mediated byendogenous pyrogens released by the cells of the host .A number of hormones like mediators (cytokines) in cellular and immunologic adaptations havebeen identified as endogenous pyrogens. They are Interleukins 1 and 6 ( IL 1 and 6 ),Interferon (IFN) , tumor necrotizing factor ( TNF) and other cytokines.The mechanism by which these cytokines raise the thermoregulatory set point seems to bethrough stimulation of prostaglandin synthesis and turnover in both thermoregulatory(brain) and nonthermoregulatory ( peripheral) Tissue.10. If given a case study of a patient with an HEENT, Respiratory, or GU infection,be able to identify the most common organisms that can cause disease.There are a whole bunch of different organisms that cause dz. If you refer to table 9-4 onpage 295 in McCance, there is a list. I will list some common ones for each.GU: e-coliHEENT: herpes simplex, fungal, ChlamydialRespiratory: Tuberculosis, Influenza, C. pneumoniae Page 5 of 5

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