Chapter 11: Interactions between Microbes and Humans (Step one of beocming established - portals of entry down to infection types)

What is step one of Steps Involved When a Microbe Causes Disease in a Host? What are the two types of entry?

1. Portal of entry: the route that a microbe takes to enter the tissues of the body to initiate an infection

• Exogenous: Organisms coming from outside the body

• Endogenous: Organisms coming from somewhere in the same human host (Microbes in body turn on us becoming opportunistic infections)

In the portals of entry step Majority of pathogens have adapted to a what? What happens if they enter the wrong portal? Provide an example

• The majority of pathogens have adapted to a specific portal of entry, one that provides a favorable habitat for further growth and spread

• If certain pathogens enter the “wrong” portal, they will not be infectious:

• Inoculation of the nasal mucosa with the influenza virus will result in the flu, but if the virus contacts the skin, no infection occurs

For portal of entry step occasionally an infectious agent can enter what? What are the two examples?

Occasionally, an infectious agent can enter by more than one portal:

• Mycobacterium tuberculosis can enter through both the respiratory and gastrointestinal tracts

• Streptococcus and Staphylococcus can enter through the skin, urogenital tract, and the respiratory tract

What is an infectious dose (ID)? Microorganisms with smaller infectious doses have what? Do different pathogens have different IDs?

• Infectious dose (ID): The minimum number of microbes necessary to cause an infection to proceed

• Microorganisms with smaller infectious doses have greater virulence

• Different pathogens do have different IDs

For the second step of attaching to host cells what is the process microbes use to attach to host tissues? What is it dependent on? Is binding specific?

Adhesion:

• Process by which microbes gain a more stable foothold on host tissues

• Dependent on binding between specific molecules on both the host and pathogen (Binding if very specific)

For the second step of attaching to host cells what are pathogens limited to? What is firm attachment a prerequisite for?

• Pathogen is limited to only those cells (and organisms) to which it can bind

• Firm attachment is almost always a prerequisite for causing disease, since the body has so many mechanisms for flushing microbes from tissues

What are the adhesion mechanisms for the three groups of microbes?

1. Bacterial, fungal, and protozoal pathogens attach by:

• Fimbriae (pili)

• Surface proteins

• Adhesive slimes or capsules

2. Viruses attach specialized receptors

3. Parasitic worms fastened by suckers, hooks, and barbs

For step three of Surviving Host Defenses what are phagocytes? And what are the three antiphagocytic factors?

• Phagocytes: white blood cells that engulf and destroy host pathogens

• Antiphagocytic factors:

1. Leukocidins: kill phagocytes outright

2. Extracellular surface layer (slime or capsule) makes it difficult for the phagocyte to engulf the pathogen

3. Some captured bacteria survive inside the phagocyte to hide from immune systems then multiply inside and release later

For the fourth step Causing Damage (Disease) what are the three ways that microorganisms cause damage to their host it’s tissues?

1. Directly through the action of enzymes or toxins produced by the infecting microbe (both endotoxins and exotoxins)

2. Indirectly by inducing the host’s defenses to respond excessively or inappropriately to cause further damage

3. Epigenetic changes made to host cells by microbes (cause genetic changes to infected tissues)

For step four Causing Damage (Disease) what are Exoenzymes (extracellular)? What and why do they dissolve?

• Enzymes secreted by microbes that break down and inflict damage on tissues

• Dissolve the host’s defense barriers to promote the spread of disease to other tissues

What are examples of Exoenzymes used in step four Causing Damage (Disease)?

1. Mucinase: digests the protective coating on mucous membranes then pathogens attach to tissue

2. Hyaluronidase: breaks down/digests the substance that cements animal cells together and fills the gaps between them

3. Coagulase: causes clotting of blood or plasma (pathogens hide in clots to get past immune system)

4. Kinase: dissolves fibrin clots

What are bacterial toxins? What is a toxin? What are the 4 exotoxins and their targets?

• Bacterial Toxins: A Potent Source of Cellular Damage

• Toxin: a specific chemical product of microbes that is poisonous to other organisms

• Toxins are named according to their target:

1. Neurotoxins act on the nervous system.

2. Enterotoxins act on the intestine

3. Hemotoxins lyse red blood cells

4. Nephrotoxins damage the kidneys

For the fourth step Causing Damage (Disease) where are Lipopolysacchardies (LPS) found? What type of effects do they have and what are examples?

• Lipopolysaccharide (LPS), part of the outer membrane of gram-negative cell walls

• Has a variety of systemic effects (effects whole body) on tissues and organs

• Causes fever, inflammation (lead to septic shock/sepsis), hemorrhage, and diarrhea

What blood infections are caused by fatal endotoxin shock?

Blood infections by Salmonella, Shigella, Neisseria meningitidis, and Escherichia coli are particularly dangerous and can lead to fatal endotoxic shock

For the fourth step Causing Damage (Disease) what are the traits of the first 4 characteristics for EXOTOXINS? (Used for comparing Exotoxins and Endotoxins)

1. Toxicity: Toxic in minute amounts

2. Effect on the body: Specific to a cell type (Blood, liver, nerve); induces TNF production resulting in fever

3. Chemical Composition: Small proteins

4. Heat Denaturation at 60 degrees Celsius: Unstable

For the fourth step Causing Damage (Disease) what are the traits of the Last 5 characteristics for EXOTOXINS? (Used for comparing Exotoxins and Endotoxins)

5. Toxoid Formation: Can be converted to toxoid

6. Immune Response: Stimulate antitoxins

7. Fever stimulation: Usually not

8. Manner of release: Secreted from live cell

9. Typical sources: A few GM+ and GM-

For the fourth step Causing Damage (Disease) what are the traits of the first 4 characteristics for ENDOTOXINS? (Used for comparing Exotoxins and Endotoxins)

1. Toxicity: Toxic in high doses

2. Effects on the body: Systemic: fever, inflammation

3. Chemical composition: Lipopolysacchraide of cell wall

4. Heat denaturation at 60 degrees Celsius: Stable

For the fourth step Causing Damage (Disease) what are the traits of the Last 5 characteristics for ENDOTOXINS? (Used for comparing Exotoxins and Endotoxins)

5. Toxoid formulation: Cannot be converted to toxoid

6. Immune response: Does not stimulate antitoxins

7. Fever stimulation: Yes

8. Manner of release: Released by cell via shedding or during lysis

9. Typical Sources: All GM- bacteria

What are the nine categories of comparison when comparing endotoxins and exotoxins?

1. Toxicity

2. Effects on body

3. Chemical composition

4. Heat Denaturation at 60 degrees Celsius

5. Toxoid formulation

6. Immune response

7. Fever stimulation

8. Manner of release

9. Typical sources