Microbiology Chapter 15 Objectives

The ID50 is the infectious dose for 50% of a sample population. It is not an absolute value, it is used to compare relative virulence under experimental conditions.

Define ID50 , its limitatons, and explain its signifcance

The lethal dose for 50% of the inoculated hosts within a given period. The potency of a toxin is often expressed as the LD50. For example, the LD50 for botulinum toxin in mice is 0.03ng/kg; for Shiga toxin, 250ng/kg; and staphylococcal enterotoxin, 1350 ng/kg. compared to the other two toxins, a much smaller dose of botulinum toxin is needed to cause symptoms.

Define LD50, and explain its significance

It is believed that the virulence of some bacteria is aided by the production of extracellular enzymes (exoenzymes) and related substances. These chemicals can digest materials between cells and form or digest blood clots, among other functions. Coagulases are bacterial enzymes that coagulate the fibrogen in blood, forming a blood clot. This clot may protect the bacterium from phagocytosis and isolate it from other defenses of the host. Bacterial kinases are bacterial enzymes that break down fibrin and thus digest clots formed by the body to isolate the infection. Hyaluroniade is another enzyme secreted by certain bacteria. It hydrolyzes hyaluronic acid, a type of polysaccharide that holds together certain cells of the body, particularly cells in connective tissues. Another enzyme, collagenase, produced by several species of Clostridium, faciliatates the spread of gas gangrene. Collagenase breaks down the protein collagen, which forms connective tissue of muscles and other body organs and tissues.

List and describe the action of the various enzymes that enable entry into the host

How many organisms entered? Few means a disease is unlikely but large amounts may mean that there is an increased potential for disease.

List considerations for disease potential

Bacteria, fungi, protozoa, worms, viruses, and prions.

List examples of external pathogens.

Microbes need iron. Siderophores (also a virulence factor). Iron bound to carriers and hemoglobin. Siderophores bind iron more tightly bind to receptors on bacteria in bacteria. Some have receptors for iron carriers and some release toxins that cause death and iron release.

List examples of virulence factors that enable microbes to use the host's nutrients.

By using the host's nutrients, by causing direct damage in the immediate vicinity of the invasion, by producing toxins, transported by blood and lymph, that damage sites far removed from the original site invasion, and by inducing hypersensitivity reactions.

List the four ways microbes cause disease

Adherence (adhesion or attachment): enable attachment of microbe to host (type of virulence factor). Adhesion factors, adhesins, or ligands that bind to receptors on host cells. Biofilms enable attachment. If alter adhesion or receptor can prevent disease.

List the types of adhesion factors and the roles they play in infection

Capsules, coagulases, and biofilm formation.

List three virulence factors that enable microbes to resist phagocytosis

A-B toxins were the first toxins to be studied intensively and are so named because they consist of two parts designated A and B, both are which are polypeptides. Most exotoxins are A-B toxins. The A part is the active (enzyme) component, and the B part is the binding component. Membrane-disrupting toxins cause lysis of host cells by disrupting their plasma membranes. Some do this by forming protein channels in the plasma membrane; others disrupt the phospholipid portion of the membrane. Superantigens are antigens that provoke a very immune response. They are bacterial proteins that combine with a protein on macrophages; this nonspecifically stimulates the proliferation of immune cells called T cells. These cells are types of WBCs that act against foreign organisms and tissues.

Outline the mechanisms of action of A-B toxins, membrane-disrupting toxins, and superantigens, explain their role in virulence, and the symptoms each causes

Exotoxins are named on the basis of several characteristics. One is the type of host cell that is attacked. Some exotoxins are named for the diseases with which they are associated. Examples include diphtheria toxin (cause of diphtheria) and tetanus toxin (cause of tetanus). Other exotoxins are named for the specific bacterium that produces them, for example, bacterium toxin (Clostridium botulinum), and Vibrio enterotoxin (Vibrio cholerae).

Classify diphtheria toxin, erythrogenic toxin, botulinum toxin, tetanus toxin, Vibrio enterotoxin, and staphylococcal enterotoxin.

The respiratory tract is the easiest and most frequently traveled portal of entry for infectious microorganisms. Microbes are inhaled into the nose or mouth in drops of moisture and durst particles. Microorganisms can gain access to the GI tract in food and water and via contaminated fingers. Most microbes that enter the body in these ways are destroyed by hydrochloric acid and enzymes in the stomach or bile and enzymes in the small intestine. Those that survive can cause disease. The genitourinary tract is a portal of entry for pathogens that are contracted sexually. Some microbes that cause STIs may penetrate an unbroken mucous membrane, while others require a cut or abrasion.

Compare and contrast pathogen entrance via different mucous membranes.

Exotoxins are produced inside some bacteria (mostly gram-negative) as part of their growth and metabolism and are secreted by bacterium into their surrounding medium or released following lysis. Exotoxins are proteins, and many enzymes that catalyze only certain biochemical reactions. Because of the enzymatic nature of most exotoxins, even small amount are quite harmful because they can act over and over again. Exotoxins are among the most lethal substances known. Endotoxins, endo- means within, in this context referring to the fact that the endotoxins are part of bacterial cells, and not metabolic production. Endotoxins are part of the outer portion of the cell wall of gram-negative bacteria.

Compare and contrast the nature and effects of exotoxins and endotoxins, and list conditions caused by each

Virulence: the degree of pathogenicity of a microorganism. Virulence factor: properties of organism that enable virulence.

Compare and contrast the terms virulence factors and virulence

Antigenic variation: changes in surface antigens that occur in a microbial population. For example, N. gonorrhoeae has several copies of the Opa-encoding gene, resulting in cells with different antigens and in cells that express different antigens over time.

Define and give an example of antigenic variation

Invasion: a surface protein produced by Salmonella Typhimurium and E. coli that rearranges nearby actin filaments in the cytoskeleton of a host cell. Membrane ruffing: invasins of the microbe cause the appearance of the host cell plasma membrane to resemble the splash of a drop of a liquid hitting a solid surface, this is a result of disruption in the cytoskeleton of the host cell. The microbe sinks into the ruffle and is engulfed by the host cell.

Define invasins and membrane ruffing

Shock: a critical condition brought on by the sudden drop in blood flow through the body. Endotoxic shock: results from severe, generalized inflammatory response induced by bloodstream infection with gram-negative bacteria. Septic shock: a sudden drop in BP induced by bacterial toxins.

Define shock and explain the terms septic shock and endotoxic shock

Siderophore: bacterial iron-binding proteins. To obtain iron, some pathogens use proteins called siderophores. Siderophores are released into the medium, where they are the iron-transport proteins by binding the iron more tightly. Once the iron-siderophore complex is formed, it is taken up by siderophore receptors on the bacterial surface. Then the iron is brought into the bacterium; in other cases, the iron enters as part of the complex.

Define siderophores, and describe their function

Pathogenicity: the ability of a microorganism to cause disease by overcoming the defenses of a host. Virulence: the degree of pathogenicity of a microorganism

Define the terms pathogenicity and virulence.

Toxigenicity: The capacity of a microorganism to produce a toxin. Toxemia: presence of toxins in the blood.

Define the terms toxigenicity and toxemia

The microfilaments of the eukaryotic cytoskeleton are composed of a protein called actin, which is used by some microbes to penetrate host cells and by others to move through and between host cells.

Describe how bacteria use the host cell's cytoskeleton to enter the cell

Skin: some microbes gain access to the body through openings in the sin, like hair follicles and sweat gland ducts. Larvae of the hookworm actually bore through intact skin, and some fungi grow on the keratin in skin or infect the skin itself. Mucous membrane: many bacteria and viruses gain access to the body by penetrating mucous membranes lining the respiratory tract, GI tract, genitourinary tract, conjunctiva (the membrane that covers the eyeballs and lids). Most pathogens enter through the mucous membranes of the GI and respiratory tracts. The parenteral route: other microorganisms gain access to the body when they are deposited directly into tissues beneath the skin or into mucous membranes when these barriers are penetrated or injured. Punctures, injections, bites, cuts, wounds, surgery, and splitting of the skin or mucous membrane due to swelling or drying can all establish parenteral routes. The placenta typically forms an effective barrier to pathogens. Pathogens may cross the placenta and infect the fetus, which can cause spontaneous abortion, birth defects, and/or premature birth.

Describe how pathogens enter via the skin, mucous membranes, placenta, and parenteral route, and give examples of each.

Evading phagocytosis: once pathogens invade, they encounter phagocytes (host defenses). Virulence factors that resist phagocytosis: capsules (some bacteria and one fungus) that prevent phagocyte from adhering. Coagulases, enzymes that form blood clots in which to hide. And biofilm formation. And hiding within host cells.

Describe the different types of virulence factors that enable a microbe to evade host defenses

A portal of exit is the route by which a pathogen leaves the body. Just as microbes enter the body through a preferred route, they also leave the body via specific routes (portals of exit) in secretions, excretions, discharges, or tissue that has been shed. In general, portals of exit relate to the infected part of the body, with microbes tending to use the same portal for entry and exit. Portals of exit let pathogens spread through a population by moving from one susceptible host to another. The most common portals of exit are the respiratory and GI tracts. Many pathogens living in the respiratory tract exit in discharges form the mouth of nose (coughing sneezing). Other pathogens exit via the GI tract in feces or saliva. Another important route of exit is the genitourinary tract. Microbes responsible for STIs are found in secretions from the penis and vagina. Urine can also contain the pathogens responsible for typhoid fever and brucellosis.

Describe the portals of exit, and compare to portals of entry

Lysogenic conversion: the acquisition of new properties by a host cell infected by a lysogenic phage. As a result of lysogenic conversion, the bacterial cell is immune to infection by the same type of phage. In addition, lysogenic cells are of medical importance because some bacterial pathogenesis is caused by the prophages they contain. When a cell lysis, they release toxins.

Describe the process of lysogenic conversion and explain its significance in exotoxin production

Contamination is the mere presence of microbes in/on the body. An infection is when organisms evades body's external defenses, multiples, and becomes established in the body.

Describe the relationship between contamination and infection.

The capsules resits the host's defenses by impairing phagocytosis, the process by which certain cells of the body engulf and destroy microbes. The chemical nature of the capsule appears to prevent the phagocytic cell from adhering against the capsule. The cell walls of certain bacteria contain chemical substances that contribute to virulence. For example, Streptococcus pyogenes produces a heat-resistant and acid-resistant protein celled M protein. This protein is found on both the cell surface and fimbriae. It mediate attachment of the bacterium to epithelial cells of the host and helps the bacterium resist phagocytosis by WBCs. The waxy lipid (mycolic acid) that makes up the cell wall of Mycobacterium tuberculosis also increase virulence by resisting digestion by phagocytes, and the bacteria can even multiple inside phagocytes. Biofilms also play a role in evading phagocytes. Bacteria that are part of biofilms are much more resistant to phagocytosis. Phagocytes do not move through the viscous carbohydrates of the extracellular polymeric substance (EPS) of biofilms. The EPS may shield against antigens so they are not recognized by the immune system.

Describe the role that capsules, biofilms, and the cell wall components M protein and waxy lipids have in pathogenicity

Once pathogens attach to host cells, they can cause direct damage as the pathogens use the host cell for nutrients and produce waste products. As pathogens metabolize and multiple in cells, the cells usually rupture. Many viruses and some intracellular bacteria and protozoa that grow in host cells are released when the host cell ruptures. Following their release, pathogens that rupture cells can spread to other tissues in even greater numbers. Some bacteria can induce host epithelial called engulf them by phagocytosis. These pathogens can disrupt host cells as they pass through and can be extruded from the host cells by exocytosis, enabling them to enter other host cells. Some bacteria can also penetrate host cells by excreting enzymes or by their own motility; such penetration can itself damage the host cells.

Describe the three ways that pathogens cause direct cell damage and give examples of each

Portal of entry: the avenue by which a pathogen gains access to the body Portal of exit: the route by which a pathogen leaves the body.

Differentiate between portal of entry and portal of exit.

Endotoxins exert their effects by stimulating macrophages to release cytokines in very high concentrations. At these levels, cytokines are toxic. All endotoxins produce the same signs and symptoms, regardless of species of microorganism, although not to the same degree. These include chills, fever, weakness, generalized aches and even shock or death. Prostaglandins are hormonelike substances that are released by damaged cells, intensifies inflammation.

Discuss the role of cytokines and prostaglandins in endotoxin symptoms

Example: The ID50 through the skin (cutaneous anthrax) is 10 to 50 endospores; the ID50 for the inhalation anthrax is inhalation of 10,000 to 20,000 endospores; and the ID50 for GI anthrax is 250,000 to 1,000,000 endospores. These data show that cutaneous anthrax is significantly easier to acquire than either the inhalation or the GI forms.

Explain and identify the effect on ID50 if a microbe enters via a preferred portal of entry, or not.

Antioxidants are substances that ,ay protect your cells against free radicals, which may play a role in heart disease, cancer and other disease. Free radicals are molecules produced when your body breaks down food or when you're exposed to tobacco smoke or radiation.

Explain the action of antioxidants.

The waxy lipid (mycolic acid) that makes up the cell wall of Mycobacterium tuberculosis also increase virulence by resisting digestion by phagocytes, and the bacteria can even multiple inside phagocytes.

Explain the benefit of mycolic acid in the cell wall of a microbe

Virulence factors enable adherence (attachment), evading host defenses, penetration, access to nutrients (also a method -> disease).

Explain the four benefits of virulence factors to microorganisms

The genes for more exotoxins are carriers on bacterial plasmids or phages. Because exotoxins are soluble in body fluids, they cam easily diffuse into the blood and are rapidly transported throughout the body.

Explain the role of plasmids and phages in exotoxin production

Endotoxins are released during bacterial multiplication and when gram-negative bacteria die and their cells undergo lysis. Antibiotics used to treat diseases caused by gram-negative bacteria can lyse the bacterial cells; this reaction releases endotoxin and may lead to an immediate worsening of the symptoms, but the condition usually improves as liver lipase breaks down the endotoxin.

Explain the source of endotoxins and discuss the symptoms and their causes

Intoxication: a condition resulting from the ingestion of a microbially produced toxin. Antitoxin: a specific antibody produced by the body in response to a bacterial exotoxin or its toxoid. Toxoid: an inactivated toxin. Lysogenic conversion: the acquisition of new properties by a host cell infected by a lysogenic phage.

Explain the terms intoxication, antitoxin, toxoid, and lysogenic conversion

Its through a bite, cut, or injection. Kind of nothing that the body can do to defend against it.

Explain why the parenteral route is not a true portal of entry

Skin: outer layer od dead skin cells act as a barrier to pathogens. Some pathogens can enter through openings or cuts. Others enter by burrowing into or digesting outer layer of skin. Mucous membrane: line the body cavities that open to the environment. Provide a moist, warm environment hospitable to pathogens. Respiratory tract is the most common site of entry. Entry through the nose, mouth, or eyes, GI tract may be a route of entry, but the microbe must be able to survive the acidic pH of the stomach. The placenta typically forms an effective barrier to pathogens. Pathogens may cross the placenta and infect the fetus, which can cause spontaneous abortion, birth defects, and/or premature birth.

Identify and describe the portals through which pathogens invade the body.

The Limulus amebocyte lysate (LAL) assay is a test to detect the presence of bacterial endotoxins. It is important too have a sensitivity test to identify the presence of endotoxins in drugs, medical devices, and body fluids. Materials that have been sterilized may contain endotoxins, even though no bacteria can be cultured from them. The LAL assay can detect even minute amounts of endotoxin.

Identify the LAL assay, and explain its importance