Lecture 19 and 20 Flashcards
Define pathogenicity
The ability to cause disease
Define virulence
The degree of pathogenicity
What is transmission?
Pathogen leaves the reservoir and enters the host via portal of entry
What must a successful pathogen be able to do after transmission
Evade primary host defences
Adhere
What is the final step in a successful pathogens journey?
Leaving the body and returning to reservoir or new host
Give an example of infectious agents with human reservoirs
Staph. aureus, E.coli, chickenpox, hepatitis B, HIV
What is a source of infection?
Where the organism comes from in a specific outbreak or individual infection
What name is given to the source of infection from the patient’s own microbiota?
Endogenous
What is the opposite of endogenous?
Exogenous
Name a zoonotic disease from dogs/rodents
Leptospirosis (due to leptospira)
Name some diseases caused by the respiratory tract as a portal of entry
Common cold, flu, pneumoan, tuberculosis, measles
What pathogens cause gastroenteritis?
Campylobacter
Salmonella enterica/typhi
Some E.coli
What pathogen can cause dysentery?
Shigella
What type of hepatitis is food borne (person to person)
Hepatitis A
Name two genitourninary tract infections that are non-sexually transmitted.
E.coli (urninary) Candida infections (thrush)
How can some pathogens gain access through unbroken skin?
Hair follicles, sweat gland ducts
hookworm bores through skin
Some fungi grow on keratin
What are two vectors for pathogens?
Insects
Formites (medical instruments etc.)
What is infectious doese?
Numer of microorganisms required to cause disease
How is virulence expressed quantitatively?
ID 50, infectious dose for 50% of the test population
What surface molecules do pathogens produce to adhere to surfaces?
Adhesins
Where are adhesins usually found?
Fimbria/pilli, which bind specifically to cell surface receptors
What type of molecule are most adhesins?
Glycoproteins or lipoproteins
What do some pathogens do to the cell surface?
Modify it
How do some E.coli alter the cell surface in order to enable it to adhere?
Inject a protein into cells which then acts as a receptor
What % of human infections could be caused by biofilms?
Up to 65%
Name 4 biofilm associated infections
Contact lens- keratitis
Diabetic foot infection
Prosthetic heart valve endocarditis
Catheter infection
What protein in the cell wall resists phagocytosis in Streptococcus pyogenes?
M protein
What cell wall component helps Neisseria gonorrhoeae attach to and enter cells?
Opa protein
What waxy lipid reisists digestion by phagocytes and is present in mycobacterium tuberculosis?
Mycolic acid
What is the primary antibody defence of mucosa?
IgA
How do pathogens overcome IgA?
Produce IgA protease
How do pathogens evade the oxygen radicals which phagocytes use to kill them?
Produce superoxide dimutase and catalase
What name is given when surface antigens are changed by activating alternative genes?
Antigenic variation
Give 3 pathogens that show antigenic variation.
Neisseria gonorrhoeae (different opa genes)
Influenza virus
Trypanosoma brucei
What is the difference between antigenic shift and antigenic drift?
Shift is 2 strains combining
Drift is changing/evolving
What do bacteria produce to take up host iron?
Siderophores
What enzume coagulates fibrin to protect pathogen from phagocytosis?
Coagulase
What do kinases do?
Digest fibrin clots
What are spreading factors?
Pathogen produced enzymes which break down host tissues, facilitate growth and spread
What is the intracellular cement of connective tissue?
Hyaluronic acid
What spreading factor breaks down hyaluronic acid?
Hyaluronidase
What breaks down collagen?
Collagenase
Other then hyaluronidase and collagenase, name other spreading factors
Proteases, nucleases, phospholipases
What bacteria produce hyaluronidase?
Streptococcus spp, staphyloccous aureus, certain Clostridium spp
What pathogens produce collagenase?
Certain Clostridium spp (Gas gangrene)
What does Salmonella prodcue to target the cytoskeleton by altering actin in order to enter a host cell?
Invasins
What is the primary mechanism of host damage?
Toxins
What are the two main types of toxin?
Endo and exo
Whats the difference between endo and exo toxins?
Exotoxins: produced inside the cell and transported out
Endotoxins: part of the cell wall of gram-negative bacteria
What type of molecule are exotoxins?
Proteins
What do exotoxins do?
Destroy parts of host’s cell or inhibit essential functions
What amount of exotoxin is needed?
Low amounts
How do exotoxins move around the body?
Soluble in body fluids
What does the body produce in response to exotoxins?
Antitoxins (antibodies)
Other than antitoxins, how else can the body respond to exotoxins?
Heat inactivation
What are inactive exotoxins called and where are they used?
Toxoids
Vaccines
Name two vaccines with toxoids
Diptheria and tetanus vaccine
What are the three main types of exotoxin?
A-B toxins
Membrane disrupting toxins
Superantigens
Name an A-B toxin
Diptheria toxin
Name a membrane disrupting toxin
Clostridium perfringens toxin
Name a super antigen
Staphlococcal toxic shock toxin
How do A-B toxins work?
B component attaches to host cell receptor, A-B exotoxin enters by endocytosis, components separate, A part alters cell function
How does the A part of the A-B toxin alter cell function?
Inhibits protein synthesis
What does the B part of the Shiga toxin do?
Binds to host cell glycolipid in large intestine and kidney
What does the A part of the shiga toxin do?
Internalised by receptor mediated endocytosis, inactivates rRNA subunit
What does A-B endotoxins of diptheria do?
Inhibit protein synthesis in heart muscle and other cells
What does tetanus toxins (A-B endotoxins) do?
Affect neuromuscular junctions by blocking release of inhibitory neurotransmitters
What do botulim A-B endotoxins do?
Affect neuromuscular junctions, prevents release of acetyl choline
What toxin damages membrane using enzymes?
C. perfringens toxin
What toxin can form pores in host cell membranes?
Streptococcus pneumoniae pneumolysin
What do superantigens provoke?
Intense immune response
How do superantigens provoke an intense immune response?
Proliferation of T cells
What does proliferation of T cells do?
Release excessive amounts of cytokines which damage host
Give an example of a superantigen
Staphloccus aureus enteroxins: causes toxic shock syndrome
What is an endotoxin?
The lipid portion (Lipid A) of a lipopolysaccharide from gram-negative bacteria
How do endotoxins cause fever (pyrogenic response)?
Macrophage produces cytokines which induces the hypothalamus to produce prostaglandins which resets the body’s thermostat to a higher temp.
Give an example of a virus using mimicry to evade host defence.
Rabies virus attachment site resembles acetylcholine
How does HIV bind to cells?
Binds to CD4 positive cells, CD4 proteins are long and bind to sites in valleys on HIV surface, which can’t be accessed by antibodies
How do viruses effect appearance of host cells?
Lysis
Appearance of inclusion body
Syncitium formation
What are effects of virus infection on appearance of host cell called?
Cytopathic effect
Round worm causes
elephantitis
How does round worm cause elephantitis?
Blocks lymphatic circulation- lymph accumulates causing swelling
What algae produces neurotoxins
Alexandrium (produces saxitoxin)
