Chapter 15 Microbiology

Identify six mechanisms of avoiding destruction by phagocytosis.

1. Inhibit adherence: M protein, capsules 2.Kill phagocytes: Leukocidins 3.Lyse phagocytes: Membrane attack complex 4.Escape phagosome 5.Prevent phagosome -lysosome fusion 6.Survive in phagolysosome

List nine cytopathic effects of viral infections.

1: Inhibition of macromolecular synthesis 2: Release of lysosome contents 3: Inclusion bodies (site of viral synthesis/assembly) 4: Formation of fused cells (Syncytium) 5: Change in cell function - e.g. when measles virus attaches to CD4 6 cells they reduce IL-12 production 6: Some viral infected cells produce interferon 7: Viral infections can induce antigenic changes on host cell surface 8: Changes to host chromosomes, oncogenes may be added 9: Cancer causing viruses inhibit "contact inhibition" between host cells thus promoting cancer.

Outline the mechanisms of action of A-B toxins, membrane-disrupting toxins, superantigens, and genotoxins.

A-B toxins: Most exotoxins are A-B toxins. The A part is the active (enzyme) component, and the B part is the binding component. Membrane-disrupting: 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: provoke a very intense immune response. They are bacterial proteins that combine with a protein on macrophages; this nonspecifically stimulates the proliferation of immune cells called T cells. Genotoxins: cause breaks in eukaryotic DNA. This causes mutations, disrupts cell division, and may lead to cancer.

Define and give an example of antigenic variation.

Antigenic variation is the ability to alter their surface antigens. 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.

Explain how capsules and cell wall components contribute to pathogenicity.

Capsules- some bacteria make glycocalyx material that forms capsules around their cell walls; this property increases the virulence of pathogenic species Cell Wall- certain bacteria contain chemical substances that contribute to virulence. For example, Streptococcus pyogenes produces a heat-resistant and acid-resistant protein called M protein

Compare the effects of coagulases, kinases, hyaluronidase, and collagenase.

Coagulases- bacterial enzymes the clot the fibrinogen in blood. Kinases- bacterial enzymes that break down fibrin and thus digest clots formed by the body to isolate the infection. Hyaluronidase- an enzyme secreted by certain bacteria, that hydrolyzes hyaluronic acid that holds together cells of the body. Collagenase- produced by several species of Clostridium, that facilitate the spread of gas gangrene. It breaks down the protein collagen.

Contrast the nature and effects of exotoxins and endotoxins.

Exotoxins- produced inside some bacteria (gram neg) as part of their growth and metabolism and are secreted by the bacterium. Protein Endotoxins- lipid portions of lipopolysaccharides (LPS) that are part of the outer membrane of the cell wall of gram-negative bacteria (lipid A). The endotoxins are liberated when the bacteria dies and the cell wall lyses, or breaks apart.

Discuss the causes of symptoms in fungal, protozoan, helminthic, and algal diseases.

Fungal: toxins adhere to the host, their structures can stop phagocytosis and bring them immunization to antifungal drugs. Protozoan: the presence of protozoa and their waste products often produces disease symptoms in the host Helminthic: some of these organisms actually use host tissues for their own growth or produce large parasitic masses; the resulting cellular damage evokes the symptoms. Algal: a few species of algae produce neurotoxins that cause symptoms.

Define ID50 and LD50.

ID50- infectious dose for 50% of a sample population LD50- lethal dose for 50% of a sample population

How would a drug that binds mannose on human cells affect a pathogenic bacterium?

If adhesins, receptors, or both can be altered to interfere with adherence, infection can often be prevented (or at least controlled).

How can lysogeny turn the normally harmless E. coli into a pathogen?

Lysogeny is when viral DNA attaches to the plasmid in the bacteria. This can cause the bacteria to produce toxins and exhibit other new properties.

Using examples, describe the roles of plasmids and lysogeny in pathogenicity.

Plasmids: One group of plasmids, called R (resistance) factors, is responsible for the resistance of some microorganisms to antibiotics. In addition, a plasmid may carry the information that determines a microbe's pathogenicity. Lysogeny: 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.

Differentiate portal of entry and portal of exit.

Portal of entry - how microbes enter the body Portal of exit - microbes leaves in secretions, excretions, discharges, or shed tissue; commonly through respiratory and gastrointestinal tracts

Washwater containing Pseudomonas was sterilized and used to wash cardiac catheters. Three patients developed fever, chills, and hypotension following cardiac catheterization. The water and catheters were sterile. Why did the patients show these reactions? How should the water have been tested?

Pseudomonas = gram neg bacteriaThere must have been endotoxins released. The bacteria was killed but the toxin was still present

Using examples, explain how microbes adhere to host cells.

The attachment between pathogen and host is accomplished by means of surface molecules on the pathogen called adhesins or ligands that bind specifically to complementary surface receptors on the cells of certain host tissues Treponema pallidum, the causative agent of syphilis, uses its tapered end as a hook to attach to host cells

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

The microfilaments of the eukaryotic cytoskeleton (see page 98) 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.

Identify the principal portals of entry.

The portals of entry for pathogens are mucous membranes, skin, and direct deposition beneath the skin or membranes (the parenteral route).

Describe the function of siderophores.

When a pathogen needs iron, siderophores are released into the medium, where they take the iron away from iron-transport proteins

Identify the importance of the LAL assay.

can detect even minute amounts of endotoxin.

Define cytopathic effects, and give five examples.

cytopathic effects are visible effects of a viral infection on a cell; Examples are: Cause the macromolecular synthesis to cease, cause cell's lysosomes to release enzymes and destroy cell, the production of an inclusion body, formation of a large multinucleate cell called a syncytium, change cell function without visually changing cell, production of interferons, antigenic variation, chromosomal changes, and loss of contact inhibition.

Provide an example of direct damage, and compare this to toxin production.

direct damage: once inside the cell it can rupture the host cell. like E.coli, shigella, salmonella they can pass through host cell and then be extruded. or secrete enzymes that can disrupt host cells. toxins: poisonous substances. most popular way used by microorganisms. travels by blood or lymph. inhibit protein synthesis, destroy blood cells and blood vessels and disrupt nervous system

How does E. coli cause membrane ruffling?

disruption in the cytoskeleton of the host cell

Food poisoning can be divided into two categories: food infection and food intoxication. On the basis of toxin production by bacteria, explain the difference between these two categories.

food infection: microorganisms cause the problem food intoxication: the toxicness of the microorganism causes the problems

Many vaccines provide years of protection against a disease. Why doesn't the influenza vaccine offer more than a few months of protection?

its antigens change very often.

Would you expect a bacterium to make coagulase and kinase simultaneously?

no, they are opposites.

What function do capsules and M proteins have in common?

protect the bacteria cell

How does toxigenicity differ from direct damage?

toxigenicity is the ability for something to cause damage or be toxic; direct damage is the damage done to the host