Chapter 16 - Host-Microbe Interactiosn

What is pathology?

• study of disease

What is etiology?

• cause of the disease

What is pathogenesis?

• how a disease develops 

What is a pathogen?

• organism that can cause disease

What is pathogenicity?

• the ability to cause disease

What is virulence?

• the ability to cause harm (severity of disease)

What is infection?

• the growth of pathogens in the body

What is disease?

• an abnormal state where the body isn’t capable of performing normal functions

What is normal microbiota?

• permanent residents 

What is transient microbiota?

• not permanent but present for days, weeks, or months

What is microbiota? (1.1)

• the variety of organisms living in different parts of the body - localized

  • generally exposed areas

What is the role of the microbiota? (1.2)

• benefits the host by preventing growth of pathogens

  • microbial antagonism

  • competitive exclusion

What is microbial antagonism?

• members of the microbiota produce substances harmful to invading microbes 

What is competitive exclusion?

• microbiota use up available nutrients to prevent the growth of pathogens 

What are opportunistic pathogens? (1.3)

• microbes that are part of the normal microbiota and don’t normally cause disease but can if

  • transferred to another part of the body

  • human host becomes immunocompromised

  • normal microbiota is disturbed

What is the progression of infectious disease? (5)

• incubation period

• prodromal period

• period of illness

• period of decline

• period of convalescence 

What is the incubation period?

• time between infection + first signs of symptoms

What is the prodromal period?

• early mild symptoms

What is the period of illness? (3)

• most severe signs + symptoms

• active immune response - may cause signs + symptoms

• if disease is not overcome → death

What is the period of decline? (3)

• signs + symptoms subside

• can last hours or days

• vulnerable to secondary infections

What is the period of convalescence?

• recovery occurs

• pathogen can still be present + spread to others

  • can be carried for months or years

Why is the number of microbes important? (2)

• too few microbes - immune system fights them off + prevents disease

• more microbes = more likely to get disease

What is ID₅₀?

• Infectious dose - causes infection in 50% of population 

  • number of pathogens needed to cause infection in 50% of population

What is LD₅₀?

• lethal dose - potency of a toxin - kills 50% of infected population

What are mechanisms of pathogenesis? (1.2 + 1.3)

• establishing infection

  • adherence 

  • invasiveness 

• invasion - portal of entry

  • mucous membranes

  • skin

  • parenteral route

What is adherence? (1.1)

• adhesins - surface molecules that allow a pathogen to attach

  • stick to specific receptors on a host cell surface

What is invasiveness? (1.1.2)

• ability of a pathogen to invade + multiply in tissues

  • two types of molecules promote invasiveness

    • extracellular enzymes (exoenzymes)

    • invasin

What are exoenzymes? (1.3)

• extracellular enzymes - degrade or alter host cells + tissues

  • fibrinolysin - degrades fibrin clots

  • collagenase - degrades connective tissue

  • coagulase - promotes blood clots around bacterial cell

What are invasins? (1.1)

• surface proteins that cause rearrangement of the host cells cytoskeleton

  • forces the host to take in the bacterium

How are mucous membranes portals of entry? (4)

• respiratory tract - most common portal - inhaled through mouth or nose

• gastrointestinal tract - germs enter food or water 

• genitourinary tract - STIs - require a broken mucous membrane

• conjunctiva - membrane covering eye 

How is skin a portal of entry? (1.2)

• unbroken skin - impenetrable by most microbes

  • some can cause infections of hair follicles

  • most need wound to enter

What is the parenteral route?

• most microbes deposit directly → tissue when skin/membrane is broken

What are exotoxins? (1.2)

• proteins excreted by bacteria

  • generally heat sensitive

  • can be extremely toxic

What are the categories of exotoxins? (3)

• neurotoxins

• enterotoxins

• cytotoxins 

What are neurotoxins? (1.2)

• exotoxins that interfere with nerve impulses

  • botulinum toxin - flaccid paralysis

  • tetanus toxin - rigid paralysis

What are enterotoxins?

• exotoxins that modify intestinal cells to continuously secrete water

What are cytotoxins?

• general cell killers

What are endotoxins? (1.3.1)

• lipopolysaccharides - part of gram negative bacteria outer membrane

  • doesn’t cause problems when embedded

  • released when bacteria die

  • can trigger fever, inflammation, hemorrhaging, shock

    • not as potent as exotoxins 

Compare exotoxins + endotoxins (1.3 + 1.3)

• Exotoxins

  • proteins

  • released outside cell

  • extremely toxic

• Endotoxins

  • lipopolysaccharides

  • released when bacteria die

  • not as toxic