pathogenicity

Question 1

mention some portals of entry

Answer 1

mucous membranes: respiratory tract, genitourinary, digestive and conjuctivae
skin
parenteral route
vertically transmitted infections- transplacental

Question 2

what is the infectious dose?

Answer 2

titre of microorganism that initiates detectable symptoms, antibody or other response in 50% of a sample population.

ID50 and also expressed as virulence

Question 3

what is LD50

Answer 3

Potency of the toxins. titre of organism that kills 50% of a sample population. Lethal dose

Question 4

bacterial adherance to cells

Answer 4

Attach to specific receptors (usually carbs) using adhesins (located on pili, fimbrae or flagella) or ligands. These can be glycoproteins, lipoproteins.

Biofilms: Cells bound within a sticky web of polysaccharide. requires sufficient amount of bacteria (quorum). adhere to living and non living surfaces. found on teeth, indwelling catheters

Question 5

Used for penetration into the host cell

Answer 5

Capsule-antiphagocytic
Cell wall structures
-mycolic acid
- M protein
- opacity Proteins
Enzymes
-coagulases
- kinases
-IgA proteases
- hyaluronidases
-collagenase

Question 6

Explain the role of mycolic acid in penetration into the host

Answer 6

resists digestion by phagocytes, can multiply in phagocytes

Question 7

M proteins in penetration into the host

Answer 7

• M proteins: Major type proteins. anchored in cell membrane and portrude through the cell surface. interfere with phagocytosis by blocking he binding site for complement protien C3b

Question 8

Opacity proteins in penetration into the host

Answer 8

Membrane protein that mediate firm attachment/binding to epithelial and phagocytic cells.

Question 9

Coagulases in penetration into host and bacterial species example

Answer 9

convert fibinogen to fibrin
isolate bacteria eg bacterial abscess, and protect from phagocytosis via fibrin layer around them
staphylococcus aureus

Question 10

Bacteria species with M proteins in cell wall

Answer 10

Streptococcus pyogenes

Question 11

Bacterial species with Opa proteins

Answer 11

Neisseria gonorrhoeae

Question 12

kinases in penetration into host and bacterial species examples

Answer 12

breakdown fibrin formed by the body to isolate infection
streptokinase: streptococcus pyogenes
staphylokinase: staphylococcus aureus

Question 13

hyaluronidases in penetration into host cell

Answer 13

hydrolyze hyaluronic acid in matrix holding together connective tissue thereby helping bacteria to spread

Question 14

collagenase in penetration of host cell and example of species

Answer 14

break down collagen in connective tissue and organs. example Clostridium species

Question 15

IgA proteases in penetration into host and examples of bacteria species

Answer 15

IgA protease helps prevent reaction where IgA produced by host traps bacteria in mucus

Neisseria gonorrhoeae and Neisseria menengitidis

Question 16

what are antigenic and phase variation and their function

Answer 16

process by which some infectious agents change their surface antigens
help in evading adaptive immunity and may contriute to dissemination (spread)

Question 17

specific definition of phase variation and antigenic variation

Answer 17

phase varitaion- switch on or off the expresssion of some components– allows expression of a given phenotype to be switched on or off

antigenic variation - alter the antigenic structure–expression of a number of alternative forms of an antigen on the cell surface, found in Neisseria gonorrhoeae

Question 18

how pathogens damage host cells

Answer 18

using their nutrients
direct damage in immediate vicinity of invasion
produce toxins
induce hypersensitivity reactions

Question 19

what are siderophores

Answer 19

small protein iron chelators, secreted to retrieve iron away from the iron transport proteins ( heme proteins and iron chelating proteins).
iron-siderophore complex is then taken up by siderophore receptors on the surface.
iron may be realesed from the complex or used to produce toxins that destroy host cells and release iron.

Question 20

how bacterial cells cause direct damage to host cells

Answer 20

produce toxins, enzymes, their metabolism and multiplication in host cells, inducing host cells to engluf them and use them as transport, spreading throughout host

Question 21

types of exotoxins

Answer 21

super antigens, AB toxins and Membrane disturbing toxins

Question 22

AB toxins

Answer 22

Dimeric, made of active and binding compenent. Made inside bacterial cell and then excreted. B part is used to bind to a specific cell surface receptor and A enters goes within the cell and inhibits protein synthesis and kills the host cell. Its main targets are the ribosomes, transport mechanisms and cell signaling. Tissues targeted by AB toxins are very defined and limited.

Question 23

Superantigens- how they work

Answer 23

modulate the activity between APC and helper T cells by interacting between the MHC, CD4 and TCR(T cell recepetor) interaction. It acts as a somewhat stimulatory mechanism to enhance this interaction and stimulate the ploriferation of T cells (increase in number) leading to a great release of cytokines.
These hormones regulate the immune response (inflammatory response) nad cell to cell communication—> increase leads to negative symptoms such as fever, nausea, diarrhoea, vomiting, shock and death.

Question 24

how membrane disrupting toxins work and examples.

Answer 24

these cause lysis of host cells by causing direct effects on their membrane. Some form protein channels/ pores eg Staphylococcus aureus and others affect the phospholipid bilayer eg Clostridium perfringens

Question 25

2 types of membrane disrupting toxins produced and example of who they’re produced by and name of toxin

Answer 25

Leucocidins- kill WBC eg staphylococci and streptococci
Haemolysins- kill RBC- produced by eg.streptococci. These procued by streptococci are called streptolysin O and streptolysin S

Question 26

examples of bacteria that release AB toxins

Answer 26

Clostridium tetani, staphylococcus aureus

Question 27

examples of bacteria that release superantigens and diseases they cause

Answer 27

staphyloccus aureus - toxic shock syndrome, food poisining

Question 28

production of endotoxins

Answer 28

lipid A portion of LPS in outer membrane is the endotoxin. released when bacterial cells die and lyse and during multiplication.

Question 29

symptoms of endotoxins

Answer 29

produce same signs and symptoms no matter the species. chills, fever, weakness, generalized aches, shock and death.

Question 30

how endotoxins work

Answer 30

• binds to macrophage, activates release of cytokines. interleukins stimulate the hypothalamus to raise temp leading to fever. other cytokines increase capillary permeability and vasodilation leading to low blood pressure. sustained low BP leads to multi organ failure and then septic shock.
• activate complement system–> histamine release, increase in inflammation and edema (leads to hypotension)
• activates tissue factor III and others –> blood clot formation and decrease in clotting proteins–> Disseminated Intravascular Coagulation DIC