Bacterial & Viral Pathogenesis Flashcards
1
Q
Define epidemiology
A
Study of occurrence, distribution and control of diseases in populations
2
Q
What are the basic stages of pathogenesis for microbial Disease
A
- Entry into the body
- attachment/adhesion to cells
- infection/colonisation and growth
- pathological alterations of host = symptoms
3
Q
Name some non-specific virulence factors
A
Extracellular proteins
Polysaccharide capsule (protection)
Toxins - damage inducing substances
4
Q
Give some examples of pathogenic extracellular proteins
A
Hyaluronidase Processes, Nucleases, Lipases etc. Collagenase Streptokinase Coagulase
5
Q
What is Glycocalyx
A
Glycoproteins and glycolic is covering that surrounds cell membrane of some bacteria
6
Q
What are the 3 types of Toxin
A
Exotoxins
Endotoxins
Enterotoxins
7
Q
What are the 3 types of exotoxins
A
Cytolytic, A-B and superantigen toxins
8
Q
Describe the function of Cytolytic toxins
A
Lose host cells by enzymatically degrading cellular components
9
Q
Describe the function of A-B toxins
A
Consist of two Covenanter bonded subunits, A(ctive) and B(inding). B subunit usually binds to cellular surface to allow transport of A through membrane to damage cell
10
Q
Describe function of superantigen toxin
A
Stimulate large amounts of immune response cells that lead to massive inflammatory reactions
11
Q
Describe enterotoxins
A
Exotoxins affecting host small intestine
- produced by food poisoning and intestinal pathogens, bacteria including staph, clostridium, bacillus, vibrio chlorae, E. coli, salmonella etc.
12
Q
Describe endotoxins
A
Produces only by gram negative organisms
- located in the outer layer of cell envelope of lysed gram negative bacteria
13
Q
Describe the effect of endotoxins
A
- released when lysed
- causes diarrhoea,rapid decrease in leukocyte and lymphocyte and platelet numbers, release of cytokines and systematic inflammation
- haemorrhagic shock and tissue necrosis (after high doses of endotoxins)
14
Q
What is bloat
A
Uncontrolled increase of body size due acc. Of gases in body as a result of pathology or death
15
Q
What is putrefaction
A
The decomposition of proteins by putrefying (anaerobic) resulting in the formation of polyamines with putrid odour - putrescine
16
Q
What is gnotobiology
A
raising mammals under germ-free environments, or conditions with controlled spectra and numbers of microorganisms
17
Q
Reasons for gnotobiology
A
Use genetically modified model systems
Study establishment and maintenance of immune system
Provide new insights on aetiologies
18
Q
Health and disease are two different states of the body, what is the word for health —> disease
A
Pathogenesis
19
Q
Health and disease are two different states of the body, what is the word for disease —> health
A
Convalescence
20
Q
Define pathogenesis
A
Set of mechanisms by which an etiological factor causes a disease
21
Q
Define epidemiology
A
The study of occurrence, distribution and control of diseases in populations
22
Q
What are the 3 types of human-microbe interactions
A
Parasitic: one organism lives and benefits at expense of other
Symbiotic: both organisms benefit from each other
Commensals (Maybe opportunistic): neither organism particularly benefits or suffers or one can benefit with no obvious harm to other
23
Q
Define virulence
A
Extent of pathogenicity expressed by pathogens
24
Q
Define pathogenicity
A
Ability of pathogens to cause disease
25
Define attenuation
Long cultivation of pathogens in culture
26
Define ID50
Infectious Dose 50%: number of pathogens cells needed to cause 50% of host cells to show signs of infection
27
Define LD50
Lethal Dose 50%: the number of pathogen cells needed to cause 50% of host cells to die
28
Define infection
The colonisation of host by a pathogen
29
Define incubation period
The time between infection and symptoms of disease
30
Define acute period
Height of disease with pronounced symptoms
31
define Decline period
Symptoms subside
32
define Convalescence period
Returning to normal
33
How are microbes like E. Coli aides during adhesion
They produce adhesins that bind to host receptors on specific sugars present in fimbriae and pili
34
What is sepsis
Viraemia
Bacteraemia
Parasitaemia
35
What is toxicity in terms of pathogenicity
Aiding disease by different toxins that inhibit or kill host cells
36
What is invasiveness in terms of pathogenicity
Growing in a tissue to such amounts of cells that inhibit host functions and cause disease (even in the absence of toxins)
37
The action of toxins can be:
Direct: causing lysis or apoptosis to cells
Indirect: triggering biological activities that harm the host systematically
38
What is the significance of a polysaccharide capsule in terms of virulence
It takes over 10,000 unencapsulated bacteria to kill a mouse but it the bacteria is encapsulated then it can take less than 10.
39
What is mycolic acid
Each material in cell walls of mycobacterium that can inhibit phagocytosis by antibiotics
40
True or false: exotoxins and enterotoxins are proteins
False: ENDOtoxins and Enterotoxins are
41
True or false: Exotoxins are lipopolysaccharides
True
42
True or false: exotoxins are less potent than endotoxins
False, other way around
43
Do bacteria secrete endo or exotoxins
Exotoxins
44
What does Anthrax result in
Reduction of RNCs especially and and leads to destruction of surrounding tissue
- spores are highly resistant to physical and chemical agents
45
What 3 toxins are the cause of anthrax development
Protective antigen: which mediates entry is the two other proteins, Oedema and Lethal factor) which are all encoded by a plasmid
46
Describe the appearance of anthrax colonies
Gram positive, with characteristic squared ends and ellipsiidal central endospores (resistant to staining and refactor to light)
- Large cells
- older colonies have ground glass phenotyoe
47
What does oedema factor (EF) do
Ca2+ and calmodulin dependant.
| Increases cAMP —> upsets water homeostasis —> liquid accumulation
48
What does lethal factor (LF) do
Inactivated MAPK kinase —> fall in cellular signalling —> impaired macrophage function —> distorted immune system
49
What are the 3 main types of anthrax
Gastrointestinal
Inhalational
Cutaneous
50
How quickly can death account after inhaling anthrax bacilli
Inhalation of spores will lead to haemorrhagic pneumonia and death within 24 hours after the flu like stage that lasts for 2-4 days
51
Characteristics of Botulism
Flaccid paralysis of muscles and respiritory failure
- caused by botulinum toxin of anaerobic bacterium Clostridium botulinum
- usually through contaminated food
52
Characteristics of Clostridium botulinum
Anaerobic organism, heterogenous group, spire forming
- under anaerobic conditions, spores can germinate under salt
- at least 7 antigenicallu distinct botulinum exist A - G.
- Types A, B, E and F are associated with human botulism
53
What is the most poisonous substance known
Botulinum toxin, 1 gram can kill 10 Million people
54
Characteristics of infant botulism
Most common form associated with consumption of contaminated food (usually honey or corn syrup)
Flaccid paralysis and respiratory arrest can develop, with rare death.
55
How is botulism diagnosed
Search for Clostridium bacteria
- toxin bioassay works in mice, not in infant or wound botulism.
- demonstrate toxin presence in serum or stool by injecting either into mice and searching for botulism
56
How is botulism treated
Early diagnosed food borne and wound can be treated with horse derived antitoxin which blocks the action of toxin
- removing contaminated food from gut
- wounds should have bacteria surgically removed
- NOT with antibiotics as they promote paralysis
57
Characteristics of Diphtheria infection
Caused by corynebacterium diphtheriae
- bacteria multiply on epithelial cells of pharynx and cause local damage
- local inflammation with false membrane, sometimes bleeding
- life threatening complication is respiratory obstruction, myocarditis, fever and exhaustion
58
Characteristics of cutaneous diphtheria infection
Bacteria colonised skin and subcutaneous tissue, developed Papua’s evolves into bronco ulcer that doesn’t heal. The exotoxins May cause systemic disease
59
Treatment and control of respiratory diphtheria infection
- Early administration of antitoxin
- Penicillin and erythromycin
- Immunisation with toxoid vaccine is recommended in childhood with boosters ever decade
- immunity determines by Schick test
60
True or false: staph epididimis secretes coagulase
False: Steph coccus does
61
Describe enterotoxins
Endotoxins that cause gastrointestinal distress when ingested. Cause massive secretion if fluid in SI lumen —> vomiting and nausea
- mostly superantigen that activate T cells —> prod cytokines and stim macrophages
62
When toxic shock syndrom usually occur
After infection during surgery By toxic shock syndrome toxin-1 (TSST-1) which is released by growing cells of s aureus
63
What is leukocidin
A protein (produced by staph aureus) that destroys leukocytes. The process cause pus prod in skin boils
64
What do carotenoids of staph aureus do
Destroy phagocytes like macrophages
65
Name some reasons for antibiotic resistance (of staph aureus)
- plasmids as well as chromosomes provide resistance against aminoglycosides, penicillins and chloramphenicol
- use of antibiotics causes natural selection against it
66
What is the usual reason for MRSA being resistant
Due to a mobile element-derives chromosomal mecA gene encoding a Penicillin Binding Protein with altered (reduced) affinity to penicillin beta-lactam rings
67
Characteristics of a carbuncle
Infection involves several adjacent hair follicles, central necrotic core forms large ulcer requiring antibiotics.
- local invasion of staph aureus
- outer layer of fibroblasts
68
Characteristics of endotoxins
- NOT located inside bacterial cell
- NOT a protein
- Lipopolysaccharide component in Outer leaflet of cell membrane
- released from the outside of cell when lysed
- consist of 3 subunits: Lipid A, a core polysaccharide and O-polysaccharide
69
Describe the 3 subunits of Lipopolysaccharides
Lipid A: responsible for toxicity
Core polysaccharide
O-polysaccharide: makes complex soluble and immunogenic
70
True or false: endotoxins are produced by gram negative bacteria only (with possible exceptions)
True
71
True or false: exotoxins are bound to the outside of the bacteria cell
False: they are metabolic products secreted from inside the cell
72
True or false: endotoxins are more heat resistant than exotoxins
True: stable up to 1 hour at autoclave temp (121 degrees)
| Exotoxins up to 60 degrees
73
Describe the effects on the host of an endotoxins
Fever, malaise, shock, blood coagulation
74
Describe the variable effect of exotoxins on the host
Could be a neurotoxin, cytotoxic, enterotoxins
75
True or false: exotoxins are fever inducing
False, endotoxins are
76
What are some representative diseases of exotoxins
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Botulism
Diphtheria
Cholera
Plague
Tetanus
```
77
What are some representative diseases of endotoxins
Typhoid fever
Endotoxic shock
Urinary tract infection
78
True or false: endotoxins activate nearly every non specific defence mechanism
True
- complement in alternative pathway
- coagulation
- inflammation
- cytokines and macrophage release
- B cells etc.
79
Characteristics of a retrovirus
Virus containing RNA that use reverse transcriptase for its replication
80
What family does HIV (human immunodeficiency virus) belong to
Retrovirus
81
How does HIV interact with the immune system
Destroys it by releasing HIV particles infecting and killing white blood cells, particularly CD4 surface protein expressing cells
82
Characteristics of HIV virions
Lipid Bilayer: apx. 72 viral envelope GP spikes
Core Proteins
- RT: Reverse Transcriptase
- MA (Matrix Protein P17) forms shell to inner side of membrane to ensure integrity of virion
- CA (Capsid Protein P24) assemble in hexameric rings to constitute to capsid
- NC (nucleocapsid protein or P7) is needed for RNA stability and nucleocapsid assembly
- Gp41 and Gp120 are needed to enter cell
83
Outline HIV replication in a CD4 host cell
- Entry of virion into cell
- conversion of RNA to DNA by RT
- Integration of viral DNA into host DNA by viral integrase
- Activation of T-cells leads to transcription and translation of viral genome
- assembly of new virions
84
Common features of HIV patients
```
WEight loss
Fatigue
Fevers
Weakness
Lower CD4 count
```
85
Diagnosis of HIV
```
Direct identification is hard as often integrated into host chromosome and could be kept as provirus for years.
Serological tests
- ELISA
- HIV Enzyme immunoassay
- Western blot
```
86
True or false: presence of HIV antibody doesn’t necessarily mean patient is infected with HIV
True, just means they have been exposed to it
87
Name some manifestations of HIV infection
Shingles: limited painful skin rash one one side of body with blisters
Disseminated herpes
Kaposi’s sarcoma: rare cancer of blood vessels AIDS associated
88
Major routes of HIV infection
- unprotected sexual inter course
- intravenous drug abuse
- blood transfusions, organ transplants, haemophilic therapy, tattooing, contaminated needles
- mother to baby at birth, breastfeeding milk
89
Treatment of HIV
No effective vaccine or cure for HIV or AIDS
Post exposure prophylactic is needed
HAART is a prescription medicine used
90
Describe the HAART prescription drug
Cocktail of 3-4 antiviral drugs including inhibitors of RT, Protease inhibitors, Nucleotide analogues
91
Characteristics of HAART
Stops HIV replication (coz they can’t develop multi-resistance to it)
Infected Cells can potentially live up to 60 years before they die
92
Describe Enfuviritide (anti-HIV Drug)
Fusion inhibitor composed of a synthetic peptide chain that acts by binding to the Gp41 membrane protein of HIV
93
Explain Kochs postulate
- the suspected pathogenic organism should be present in ALL cases of disease and absent in healthy animals
- suspected organism should be pure cultured
- cells from pure culture should cause disease in healthy animal
- organism should be reisolated and shown to be the same as the original
94
Examples of some pathogens that can’t be cultured in a lab
Mycobacterium leprae
| Tryponema pallidum
95
True or false: some diseases aren’t virulent by them selves
True, some are caused by combinations of factors e.g. liver cancer can be a product of Hepatitis B and D
96
What did the discovery of slide media for cultivation allow
- basic studies on biology of individual species and strains
- diagnostic purposes
- gene cloning and vaccine making
- Recognising emerging infectious diseases
97
Name the portals of entry
Skin, placenta, conjunctiva and mucous membranes of the respiratory, GI, urinary and reproductive tracts
- parenteral route is through skin puncture
98
Difference between vertical and horizontal spread of infection
Vertical is from generation to generation e.g. through gametes
Horizontal is from person to person e.g. airborne
99
Name some pathogens that can cross the placenta
Toxoplasma gondii
Treponema pallidum
Lentivirus (HIV)
Rubivirus
100
Characteristics of the epidemiological triangle
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Who what (when) where
Host, Agent [virus, bacteria etc.], (Time), environment (blood etc.)
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