Microbial Mechanisms of Pathogenicity

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Microbial Mechanisms of Pathogenicity

• Chapter 15
• Lecture 14

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Overview of Microbial Mechanisms of Pathogenicity
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Pathogenicity vs. Virulence

• Pathogenicity is the ability of a pathogen to
  cause disease by _____________ the defenses of
  the host
• Virulence is the degree and severity of
  _____________________-

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Portals of Entry

• The route a microorganism uses to gain entry to
  the host
• Many organisms can penetrate _________
  __________________ of the
• Conjunctiva
• Respiratory system
• Gastrointestinal system
• Genitourinary system

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Portals of Entry

• Respiratory Tract most ___________portal of
  entry
• Droplets and dust carry microorganisms
• Genitourinary tract through membranes
• GI tract enter with food, water, contaminated
  objects placed into mouth (fingers!)

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Portals of Entry (cont.)

• Skin which is not broken
• is an effective barrier- but microbes can
  enter through hair _____________ and ___________
  ____________.
• Exception is some fungi which inhabit the skin
• Parenteral entry bites, ___________, and wounds

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Preferred Portals

• Some microorganisms can only enter one way
• Example Salmonella preferred portal is to be
  ________________
• Rubbed on skin-only mild inflammation
• Streptococci ___________-cause pneumonia
• Swallowed-no symptoms

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LD50 or ID50

• Expressions of the virulence of a pathogen once
  it has gained entry
• Used to describe numbers of microorganisms needed
  to cause death or disease
• LD50 Lethal Dose for 50 of the ______________
  hosts (number)
• ID50 ________________ dose for 50 of the
  inoculated hosts (number)

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Adherence

• Pathogen binds to host
• Adhesins on pathogen bind to receptors on host
• Adhesins can be __________ or_______________ or
  both.
• Most common _____________ is mannose.

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Adherence
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How pathogens evade host defenses

• Capsules bacterial capsules help cells escape
  being ____________
• Proteins in the cell wall can facilitate
  ______________
• Some microbes can be phagocytized, and reproduce
  inside a phagocyte!
• And..

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Enzymes!

• Enzymes
• Leukocidins destroy neutrophils and
  __________________
• Hemolysins lyse __________ ______________
  __________
• Coagulase protects infections by causing a clot
• Kinases destroy clots
• Hyaluronidase destroys a mucopolysaccharide
  which holds cells together in ___________________
• Collagenase hydrolyses collagen connective
  tissue

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Specialized Pathogenic Invasion

• Salmonella(enteric pathogen)
• produce Invasins-which cause the
• actin (protein) in the cells cytoskeleton to
  form a kind of basket and carries the bacteria
  into the host cell!

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Salmonella
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How pathogens damage cells

• The action of pathogen can destroy cells
  outright.
• Toxin production
• Toxemia ( _____________)and toxigenicity
  (______________________)
• Exotoxins are released from growing bacteria and
  cause disease
• Endotoxins are part of the bacterial cell-usually
  the G- cell wall lipoproteins

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Exotoxins and Endotoxins
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Exotoxins

• _____________ may be produced against exotoxins
  are called antitoxins
• Ex. Tetanus antitoxin
• Cytotoxins (inhibit protein synthesis) are
  produced by diptheria organisms
• Erythrogenic toxins damage capillaries

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More Exotoxins

• Neurotoxins
• botulism toxin-inhibits nerve transmission, and
• tetanus toxin- prevents inhibitory nerve
  transmission
• Enterotoxins Vibrio cholerae and Staph induce
  ________ ___ ____________ and ______________ from
  host cells

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Exotoxins
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Endotoxins

• LPS-the lipid component of the G- cell wall
• Bacterial cell death, because of ____________ or
  _____________ cause the release of endotoxins!!!!
• Endotoxins cause
• Fevers-
• Shock-lowered blood pressure
• Allow bacteria to cross ____________-________
  ___________________

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How Endotoxins cause fever
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Plasmids, Lysogeny, Pathogenicity

• RECALL Plasmids may carry genes for antibiotic
  resistance, toxins, capsules, fimbriae.
• Lysogenic conversion (?) can result in bacteria
  with virulence factors, such as ability to make
  toxins or capsules.

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Nonbacterial Pathogens-Viruses

• Viruses evade the hosts immune system by growing
  ________of host cells
• Viruses attach to host cells by specific
  receptors (____________ __________)

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Viral pathogenicity

• Cytopathic effects (CPEs) are _________signs of
  viral modification of host cell. (microscope)
• Stopping of mitosis
• Lysis (death)
• Formation of inclusion (dark staining)bodies
• Cell fusion (multinucleate cells)
• Antigenic changes
• Chromosomal changes (mutations)
• Transformation
• Some viruses kill the cells outright through a
  lytic cycle.

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Cytopathic effects
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Pathogenic Fungi

• Fungal disease symptoms are due to
• Toxins
• Aflatoxin-peanuts
• Toxins-ergot
• Neurotoxins-Amanitas Death Angel mushroom
• Capsule-like formations which help to resist
  ______________________
• Allergic reactions in host triggered by presence
  of fungus
• Inhibit protein synthesis skin irritations,
  diarrhea, and lung hemorrhage-infants and water
  damaged walls
• Also enzymes- mycoses

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Pathogenic Protozoa

• Protozoan diseases caused by direct action of the
  protozoan or by its waste products
• Malaria cause __________ of cells
• Giardia ___________ host cells
• Trypanosoma causes ____________
• Both Giardia and Trypanosoma have the ability to
  ________ __ __ ________ that they can display to
  the hosts immune system!!!

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Malaria
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Trypanosoma
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Giardia
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Pathogenic Helminths

• Helminths cause physical damage
• Ex. Elephantiasis
• Worms block ________________ vessels
• Grotesque swelling of lower extremities results
• Larva migrans non-human ascarids (roundworms)
  and hookworm
• Dog and Raccoon ascaris, a helminth EID
• Eggs may cause inflammation
• Helminths may also cause toxic damage

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Elephantiasis
After Treatment
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Pathogenic Helminths
Cutaneous Larva migrans Raccoon form prefers the
brain.
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Eggs shed in liver/bill ducts
Spine provokes damage as Eggs pass to intestine.
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Pathogenic Algae

• Few species of algae produce _____________________
  _-toxin is accumulated by mollusks which eat the
  algae humans become ill after eating such
  shellfish.
• Shellfish closures for __________- ________

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Red Tide
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Summary of Microbial Mechanisms of Pathogenicity