Chapter 15

Question 1

what is pathogenicity:

Answer 1

the ability of a pathogen to produce a disease by overcoming the defenses of the host

Question 2

what is virulence:

Answer 2

the degree of pathogenicity

Question 3

How microorganisms enter a host:

Answer 3

the specific route by which a particular pathogen gains access to the body is called its portal of entry

Question 4

Portals of entry:

Answer 4

-many microorganisms can penetrate mucous membranes of the conjunctiva and the respiratory, gastrointestinal, and genitourinary tracts

Question 5

Portals of entry:

Answer 5

• most microorganisms can’t penetrate intact skin; they enter hair follicles and sweat ducts
• some microorganisms can access to tissues by inoculation through the skin and mucous membranes in bites, injections, and other wounds…this route of penetration is called the parenteral route

Question 6

The Preferred Portal of Entry:

Answer 6

-many microorganisms can cause infection only when they gain access through their specific portal of entry

Question 7

Numbers of Invading Microbes:

Answer 7

-virulence can be expressed as LD50 (lethal dose for 50% of the inoculated hosts) or ID50 (infectious dose for 50% of the inoculated hosts)

Question 8

Adherence:

Answer 8

• surface projections on a pathogen called adhesions (ligands) adhere to complementary receptors on the host cells
• adhesions can be glycoproteins or lipoproteins and are frequently associated with fimbraie

Question 9

Adherence: what is the most common receptor:

Answer 9

-mannose

Question 10

How Bacterial Pathogens Penetrate Host Defenses:

Answer 10

capsules: some pathogens have capsules that prevent them from being phagocytized

Question 11

How Bacterial Pathogens Penetrate Host Defenses:

Answer 11

cell wall components: proteins in the cell wall can facilitate adherence or prevent a pathogen from being phagocytized

Question 12

How Bacterial Pathogens Penetrate Host Defenses:

Answer 12

enzymes:
- local infections can be protected in a fibrin clot caused by the bacterial enzyme coagulase
- bacteria can spread from a focal infection by means of kinases (which destroy blood clots), hyaluronidase (which destroys a mucopolysaccharide that holds cells together), and collagenase (which hydrolyzes connective tissue collagen)
- IgA proteases destroy IgA antibodies

Question 13

How Bactetial Pathogens Penetrate Host Defenses:

Answer 13

antigenic variation:

-some microbes vary expression of antigens, thus avoiding the host’s antibodies

Question 14

How Bacterial Pathogens Penetrate Host Defenses:

Answer 14

biofilms:

- phagocytes are inactivated or killed by the EPS of biofilms

Question 15

How Bacterial Pathogens Penetrate Host Defenses:

Answer 15

penetration into the host:

-bacteria may produce proteins that alter the actin of the host cell’s cytoskeleton, allowing bacteria into the cell

Question 16

How Bacterial Pathogens Penetrate Host Defenses:

Answer 16

1) capsules
2) cell wall components
3) enzymes
4) antigenetic variation
5) penetration into the host
6) biofilms

Question 17

How Bacterial Pathogens Damage Host Cells: using the host’s nutrients: siderophores

Answer 17

-bacteria get iron from the host using siderophores

Question 18

How Bacterial Pathogens Damage Host Cells: Direct Damage

Answer 18

-host cells can be destroyed when pathogens metabolize and multiply inside the host cells

Question 19

How Bacterial Pathogens Damage Host Cells: The Production of Toxins

Answer 19

• poisonous substances produced by microorganisms are called toxins; toxemia refers to the presence of toxins in the blood. The ability to produce toxins is called toxigenicity
• exotoxins are produced by bacteria and released into the surrounding medium. Exotoxins, not the bacteria, produce the disease symptoms
• antibodies produced against exotoxins are called antitoxins
• A-B toxins consist of an active component that inhibits a cellullar process and a binding component that attaches the two portions to the target cell (eg: a diptheria toxin…helicase genotoxin)
• membrane-disrupting toxins cause cell lysis (eg: hemolysis)
• superantigens cause release of cytokines, which cause fever, nasea, and other symptoms (eg: toxic shock syndrome toxin)
• endotoxins are the lipid A component of the cell wall of gram-negative bacteria
• bacterial cell death, antibiotics, and antibodies may cause the release of endotoxins
• endotoxins cause fever (by inducing the release if interleukin-1) and shock (because of a TNF-induced decrease in blood pressure)
• the Limulus amebocyte lysate (LAL) assay is used to detect endotoxins in drugs and on medical devices

Question 20

Plasmids:

Answer 20

• “a genetic structure in a cell that can replicate independently of the chromosomes, typically a small circular DNA strand in the cytoplasm of a bacterium or protozoan. Plasmids are much used in the laboratory manipulation of genes.”
• plasmid may carry genes for antibiotic resistance, toxins, capsules, and fimbriae

Question 21

Pathogenic Properties of Viruses:

Answer 21

1) viruses avoid the host’s immune system by growing inside cells
2) viruses gain access to host cells because they have attachment sites for receptors on the host cell
3) visible signs of viral infections are called cytopathic effects (CPE)
4) some viruses cause cytocidial effects (cell death), and others cause noncytocidal effects (damage but not death)
5) cytopathic effects include stopping mitosis, lysis, formation of inclusion bodies, cell fusion, antigenic changes, chromosoma changes, and transformation

Question 22

Pathogenic Properties of Fungi, Protozoa, Helminths, and Algae:

Answer 22

1) symptoms of fungal infections can be caused by capsules, toxins, and allergic responses
2) symptoms of protozoan and helminth diseases can be caused by damage to host tissue or by the metabolic waste products of the parasite
3) some protozoa change their surface antigens while growing in a host, thus avoiding destruction by the host’s antibodies
4) some algae produce neurotoxins that cause paralysis when ingested by humans

Question 23

Portals of Exit:

Answer 23

• pathogens leave a host by portals of exit
• three common portals of exit are: the respiratory tract via coughing or sneezing, the GI tract via saliva or feces, and the GI tract via secretions from the vagina or penis
• anthropods and syringes provide a portal of exit for microbes in the blood