methods of pathogenicity

Question 1

describe interferon

Answer 1

virus invades cell
host cell produces interferon
molecule of interferon will go to second cell
second cell begins producing antiviral proteins
AVP block viral replication

Question 2

name the 4 types of adhesion molecules

Answer 2

• fimbrae
• capsule/slimelayer
• protein spikes
• flagella

Question 3

name two types of toxins and who produces them

Answer 3

endotoxin - by gram negative only

exotoxin - produced by both gram negative and positive

Question 4

describe a gram positive cell wall

Answer 4

circles
line
PEPTIOGLYCAN
CYTOPLASMIC MEMBRANE

Question 5

describe gram negative cell wall

Answer 5

endotoxin (liposaccaride)
fuzzy lines
PEPTIOGLYCAN
fuzzy lines

Question 6

name 4 cell associated virulence factors of S.aureus

Answer 6

capsule
protein A – fimbrae
fibronectin – binding protein
collagen binding protein

Question 7

name virulence factors of s.aureus

Answer 7

enterotoxins
epidermolytic toxin
TSS toxin
membrane damaging toxin (haemolysins)
leucocidin
staphlokinase

Question 8

describe HIV

Answer 8

immunosuppression
long lasting depression of humeral antibodies and CMI
antigenic variation
variation between individuals
variations within same patient
unto 108 genetic variants of HIV in AID patients

Question 9

describe gene switching

Answer 9

most dramatic form of antigenic variation
WHOLE sequence of genes coding for surface antigens switched on or off
e.g
TRYPANOSOME (sleeping sickness) has approx 1000 distinct surface molecules
organism can switch from one gene to another at roughly weekly intervalls

Question 10

describe antigenic shift

Answer 10

major changes in surface antigens caused by recombination between virus strains

e.g human influenza A strain and avian flu virus –» new strain of influenza –> influenza pandemic

Question 11

describe antigenic drift

Answer 11

small mutations in gene coding for surface antigens
reduces effectiveness of B&T cells memory built up in response to earlier infection
e.g all types of common cold or influenza

Question 12

describe antigenic variation

Answer 12

variation in surface antigen composition
various forms:

antigenic shift
antigenic drift
gene switching

Question 13

describe inflamation

Answer 13

dilation of blood vessels in infected area causes
FIBRONECTIN and white blood cells to arrive at infection site
protein rich fluid to be secreted
fibrin seals blood vessels leading from infection site
macrophages and neutrophils move towards site by chemotaxis

Question 14

describe NON specific defences of the CONJUNCTIVA

Answer 14

main defence = keep blinking
tears contain lysozyme
only need slight damage to allow organisms such as chlamydia to cause infection

Question 15

describe NON specific defences in UROGENITAL TRACT

Answer 15

bladder has no normal flora
flushing action removes organisms

VAGINA– normal microflora protects against pathogens but disturbance to normal flora can lead to thrush

Question 16

describe NON specific defences in ORAL CAVITY

Answer 16

flushing action of saliva (approx one litre per day)
lysozyme and antibodies in saliva
normal microflora
influence of diet– e.g. vitamin C deficiency

Question 17

describe NON specific defences in GI TRACT

Answer 17

constant digestive flow
removes microorganisms
acidic PH
bile salts
digestive enzymes
mucous lining gut epithelium
large population of resident bacteria
competition some produce inhibitory substances

Question 18

name 3 infections that can attack healthy skin

Answer 18

ring worm
HPV
athletes foot

Question 19

describe NON specific defence SWEAT GLANDS

Answer 19

flush microbes from the skin

lysozyme

Question 20

describe NON specific defence SEBUM

Answer 20

oil substance from salacious glands

contains fatty acids

Question 21

describe NON specific defence SKIN

Answer 21

dry, tough, salty layer PH 3-5 (ACIDIC)
normal  microflora
desquamation -- skin cells shed at rate 5X10 to power8 per day
healthy intact skin rarely penetrated 
need damage of some kind

Question 22

absence of suitable target for immune responce… describe

Answer 22

weakly immunogenic capsular antigens mask more immunogenic cell wall compounds
organisms avoid immune forces by staying inside infected cell (leprocy)
mimicry of host antigens
e.g B-heamolytic streptococci and human heart muscle – rheumatoid heart disease

Question 23

name microbial strategies to overcome immune responce

Answer 23

resistance to phagocytosis
immunosuppression
absence of suitable target for immune resource e.g possession of capsule

Question 24

name two types of defences the body has against infection

Answer 24

NON SPECIFIC (inane)

SPECIFIC (adaptive)

Question 25

name and describe RT pathogens

Answer 25

bordetella pertussis – produces toxin that paralysis cilla

influenza virus –

both have HAMAGGLUTININS on their surface attach strongly to receptor sites on lining on upper RT

Question 26

name infections caused by S.aureus

Answer 26

boils, skin septic, post operative wound infections, scaled skin syndrome, catheter associated infections

septicaemia, endocarditis, TSS, ostoeomyrlitis, phnemonia, food borne infections

Question 27

describe the mechanism of resistance to phagocytosis

Answer 27

capsule prevents contact with phagocyte
prevention of ozonisation
escape into cytoplasm
phagocyte destroyed by release of toxin

Question 28

describe the flow chart when the infection is not contained

Answer 28

spread by lymphatics – antibody formed bacteria killed

toxin produced – antibody formed, toxin neutralised,

intracellular multiplication – cell mediated immunity

ALL INFECTIONS CONTAINED BY IMMUNE RESPONCE

Question 29

MICRORGANISMS

INATE DEFENCES – entry prevented no infection
(mechanical barriers, secretions, mechanical elimination, phagocytic cells)

INVASION
local multiplication

INFLAMATION – infection contained

Answer 29

MICRORGANISMS

INATE DEFENCES – entry prevented no infection
(mechanical barriers, secretions, mechanical elimination, phagocytic cells)

INVASION
local multiplication

INFLAMATION – infection contained