methods of pathogenicity Flashcards
describe interferon
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
name the 4 types of adhesion molecules
- fimbrae
- capsule/slimelayer
- protein spikes
- flagella
name two types of toxins and who produces them
endotoxin - by gram negative only
exotoxin - produced by both gram negative and positive
describe a gram positive cell wall
circles
line
PEPTIOGLYCAN
CYTOPLASMIC MEMBRANE
describe gram negative cell wall
endotoxin (liposaccaride)
fuzzy lines
PEPTIOGLYCAN
fuzzy lines
name 4 cell associated virulence factors of S.aureus
capsule
protein A – fimbrae
fibronectin – binding protein
collagen binding protein
name virulence factors of s.aureus
enterotoxins epidermolytic toxin TSS toxin membrane damaging toxin (haemolysins) leucocidin staphlokinase
describe HIV
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
describe gene switching
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
describe antigenic shift
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
describe antigenic drift
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
describe antigenic variation
variation in surface antigen composition
various forms:
antigenic shift
antigenic drift
gene switching
describe inflamation
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
describe NON specific defences of the CONJUNCTIVA
main defence = keep blinking
tears contain lysozyme
only need slight damage to allow organisms such as chlamydia to cause infection
describe NON specific defences in UROGENITAL TRACT
bladder has no normal flora
flushing action removes organisms
VAGINA– normal microflora protects against pathogens but disturbance to normal flora can lead to thrush
describe NON specific defences in ORAL CAVITY
flushing action of saliva (approx one litre per day)
lysozyme and antibodies in saliva
normal microflora
influence of diet– e.g. vitamin C deficiency
describe NON specific defences in GI TRACT
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
name 3 infections that can attack healthy skin
ring worm
HPV
athletes foot
describe NON specific defence SWEAT GLANDS
flush microbes from the skin
lysozyme
describe NON specific defence SEBUM
oil substance from salacious glands
contains fatty acids
describe NON specific defence SKIN
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
absence of suitable target for immune responce… describe
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
name microbial strategies to overcome immune responce
resistance to phagocytosis
immunosuppression
absence of suitable target for immune resource e.g possession of capsule
name two types of defences the body has against infection
NON SPECIFIC (inane)
SPECIFIC (adaptive)
name and describe RT pathogens
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
name infections caused by S.aureus
boils, skin septic, post operative wound infections, scaled skin syndrome, catheter associated infections
septicaemia, endocarditis, TSS, ostoeomyrlitis, phnemonia, food borne infections
describe the mechanism of resistance to phagocytosis
capsule prevents contact with phagocyte
prevention of ozonisation
escape into cytoplasm
phagocyte destroyed by release of toxin
describe the flow chart when the infection is not contained
spread by lymphatics – antibody formed bacteria killed
toxin produced – antibody formed, toxin neutralised,
intracellular multiplication – cell mediated immunity
ALL INFECTIONS CONTAINED BY IMMUNE RESPONCE
MICRORGANISMS
INATE DEFENCES – entry prevented no infection
(mechanical barriers, secretions, mechanical elimination, phagocytic cells)
INVASION
local multiplication
INFLAMATION – infection contained
MICRORGANISMS
INATE DEFENCES – entry prevented no infection
(mechanical barriers, secretions, mechanical elimination, phagocytic cells)
INVASION
local multiplication
INFLAMATION – infection contained
