Chapter 15 Microbiology

What are the stages of pathogenicity?

-Gain access to host (exposure and portal of entry)

-Adhere to host tissue

-Evade host defenses

-Damage host tissues

What are the portals of entry?

1. Mucous membranes (most common)

Respiratory- entry by drops of moisture of dust particles

Gastrointestinal- entry by food, water, or contaminated fingers

Genitourinary- entry by sexual contact

2. Skin- entry by hair follicles and sweat glands, conjunctiva

3. Parenteral route- microorganisms gain access to tissues by inoculation through the skin and mucous membranes in bites, injections, and other wounds

Explain virulence

The likelihood of disease increases as the number of pathogens increase

Virulence can be expressed as LD50 or ID50

ID 50: infectious dose for 50% of the test population, number of pathogens to cause active infection

LD 50: lethal dose for 50% of the test population, number of pathogens or amount of toxin to cause death

Explain adherance

Adherence- attachment of pathogen to host tissues.

Adhesins/ligands= surface molecules on pathogens that bind to complementary surface receptors on host cells

How pathogens evade host defenses (virulence factors)

capsules, components of cell wall, enzymes, penetration into host cell

Define capsules

made of glycocalyx, impairs phagocytosis

Define components of cell wall

M proteins- aids in attachment, heat and acid resistant, resists phagocytosis

Fimbrae- attachment and blocks phagocytosis

Opa protein- attachment and entrance

Waxy lipid- resist digestion by phagocytes, mycolic acid (mycobacterium)

Define enzymes used to evade host defenses

Coagulase- coagulate blood

Kinases- digest fibrin clots

Hyaluronidase- hydrolyzes hyaluronic acid

Collagenase- hydrolyzes collagen

IgA protease- destroy IgA antibodies

Antigenic variation- alter surface proteins

Describe the process of penetration into the host cell

Penetration into the host cell cytoskeleton

After adhesions have provided attachment of pathogen

Pathogen produces invasins (surface proteins) that rearrange actin protein filaments in the host cells cytoskeleton to create a basket

Pathogen is engulfed by host cell (endocytosis)

How bacterial pathogens damage host cells

Using host nutrients, direct damage, cytopathic effects of viruses, production of toxins

How do pathogens use host nutrients

-organic molecules

Iron- siderophores (proteins produced by bacteria) takes iron away from other molecules and binds to it tightly

How do pathogens do direct damage?

-Penetration itself damages

-Metabolize in and rupture of host cell

-Produce toxins

-Produce waste

What are the cytopathic effects of viruses

stopping mitosis, formation of inclusion bodies, cell fusion, antigenic changes, chromosomal changes, lysis of host cell

Explain the production of toxins

Poisonous substances produced by certain microorganisms

Terms:

toxigenicity-ability to produce a toxin

toxemia- presence of toxin in the hosts blood

taxoid- inactivated toxin used in a vaccine

Antitoxin: antibodies against a specific toxin

What are the two types of bacterial toxins?

Exotoxins- toxic substances released outside the cell

Endotoxins- toxins composed of lipids that are part of the cell

Explain Plasmid-Lysogeny and Pathogenicity

Plasmid- carry virulence factors: toxin, R factors (resistance), enzymes

Lysogeny- dormant viral DNA cause host bacterial cell to exhibit new properties (capsule, toxin)

What are the portals of exit

Mucus Membranes

Respiratory tract (most common)- coughing, sneezing

Gastrointestinal tract- feces, saliva

Genitourinary tract- urine, vaginal secretions

Skin

Parenteral- blood (biting, arthropods, needles/syringes)

Define secretions and excretions

Pathogens exit in secretions or excretions

Secretions- process which substances are produced and discharged from

Excretions- process of eliminating waste, tissue that has been shed