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Microbiology > Topic 11 - mechanisms of pathogenicity > Flashcards

Topic 11 - mechanisms of pathogenicity Flashcards

1
Q

What are the portals of entry for microbes?

A

There are three portals of entry:

mucous membranes, skin and parenteral route (IV catheters, injections both subcut and intramuscular).

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2
Q

What are the different places microbes can enter through the body?

A

Eyes - mucous membranes (conjunctive infection)
Skin - parental route (clostrium, tetani-tetanus, hepatatitis B and C)
Genitourinary tract - mucous membranes (HIV, Herpes, Neisseria gonorrhoeae and trepponema pallidum = syphilis)
Gastrointestinal tract - mucous membrane (E.coli, Salmonella enterica, Hepatitis A virus)
Respiratory tract - mucous membranes (mycobacterium tuberculous, TB influenza, measles)
Ear, mouth and nose.

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3
Q

Identify principal portals of entry.

A

Respiratory tract - microbes travelling through aerosols and we breathe it. Tissues that line body cavities or canals such at throat, nose, mouth are more susceptible.
Skin - first line of defence and usually impenetrable if intact
Parenteral route - this by-passes the stomach, the stomach will usually destroy it so it needs to get in another way therefore injection, cut or stab wound.
GIT - mucous membrane, transmitted through food, water and dirty fingers
Genitourinary tract - mucous membrane, through sexual activity, if one partner is affected. STD’s such as HIV, genital warts, Herpes and syphilis

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4
Q

What is the preferred portal of entry?

A

Many pathogens have a preferred portal which is their prerequisite to them being able to cause disease, e.g. streptococci which is inhaled can cause pneumonia but do nothing if swallowed.

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5
Q

What is ID50 and LD50?

A

Infectious dose for 50% of test population and Lethal dose for 50% of test population.
This shows how many organisms care needed to successfully infect a host and it helps us categorise organisms according to their degree of virulence

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6
Q

The lower the LD50 the more virulent the pathogen is. True or False?

A

True.

The more virulent it is the less dosage needed therefore lower ID50 and LD50.

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7
Q

What is adherence and what are the different modes?

A

This is the first step of pathogenicity and all pathogens have means of attaching to host tissues after gaining entry.
The different modes:
- Adhesions/ligands which bind to receptors on host cells
- Glycocalyx which is in streptococcus mutans
- Fimbriae which is seen in E.coli

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8
Q

What are biofilms?

A

Biofilms are hard to remove layers which connect together different microbes. This is seen on sewage treatment plants and in teeth as plague.

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9
Q

What are the cell wall components and how do they contribute to pathogenicity?

A

M-protein: resists phagocytosis (Streptococcus pyogenes)
Opa-protein: inhibits T-helper cells (Neisseria gonorrhoeae)
Mycolic acid: waxy lipids which resist digestion (Mycobacterium tuberculosis)

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10
Q

How do capsules contribute to pathogenicity?

A 
Bacterial capsules are a form of passive defence, they prevent phagocytosis, are slippery and our immune system can't catch them.
These include:
- E.coli
- Strep. pneumoniae 
- Haemophilus influenza 
- Bacillus anthracis
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11
Q

What are the 5 bacterial enzymes?

A
  1. Coagulase- coagulates fibrinogen
  2. Kinases- digest fibrin clots
  3. Hyaluronidase - hydrolyses Hyaluronic acid
  4. Collagenase - hydrolyses collagen
  5. IgA proteases - destroys IgA proteins
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12
Q

What is antigenic variation?

A

Vary expression on surface protein. This helps avoid the host’s antibodies.

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13
Q

How does bacteria enter host cell?

A

Penetration into the host cell cytoskeleton.

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14
Q

What is invasins?

A

When host actin is altered to enter the cell, salmonella does this.
Listeria uses actin to move from one cell to another.

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15
Q

What are examples of direct damage?

A
  • Disrupt host cell function
  • Produce waste products
  • Toxins
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16
Q

Define: Toxin, toxigenicity, toxemia, toxoid and antitoxin.

A 
Toxin = poisonous substance produced by bacteria 
Toxigenicity = ability to produce toxin 
Toxemia = presence of toxin in host blood 
Toxoid = inactivated toxin used in a vaccine 
Antitoxin = antibodies against a specific toxin
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17
Q

What are the 5 requirements for infection?

A
  1. Gain access to host
  2. Establish and increase numbers
  3. Evade host immune system
  4. Destroy/damage host tissue
  5. Exit and survive to infect another host
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18
Q

What are exotoxins?

A

Toxins produced by bacteria and released into surrounding medium, they are structure and function specific in host cells, e.g. botulism and tetanus toxins.
Once the bacteria is dead exotoxin production stops.

19
Q

What are exotoxin properties?

A 
Source = Mostly gram + but some gram -
Relation to microbe = by-products of growing cells 
Chemistry = Protein 
Fever = No 
Neutralised by anti-toxin = Yes 
LD50 = small
20
Q

What are the different types of exotoxins and what are their mode of action?

A
  • Membrane-disrupting toxins which lyse host cells by making channels in plasma membrane. There are three types: leukocidins (enzymes which destroy WBC’s), Hemolysins (damage plasma membrane of both RBC’s and WBC’s) and Streptolysins (hemolysin produced by streptococcal bacteria).
  • A-B exotoxins which are made up of 2 polypeptides (A) for an active enzyme and (B) for binding component
  • Superantigens which cause T-cells to produce large amounts of cytokines
21
Q

What are endotoxins and what do they cause?

A

These are toxins in the outer membrane of the cell wall of gram negative bacteria. They are released when bacteria dies and cells lyse.
They can cause:
fever, inflammation, respiratory distress, hypotension, decreased cardiac output, irreversible shock and diarrhoea.

22
Q

What are endotoxin properties?

A 
Source = gram -
Relation to microbe = outer membrane 
Chemistry = Lipid A 
Fever = Yes
Neutralised by anti-toxin? No 
LD50 = Large
23
Q

What are the steps in the pyrogenic response?

A
  1. Macrophage ingests a gram negative bacterium.
  2. Bacterium is degraded in vacoule which releases endotoxin that induces macrophage to produce cytokines IL-1 and TNF.
  3. Cytokines are released into bloodstream by macrophages where they travel to hypothalamus
  4. Cytokines induces prostaglandin production in the hypothalamus which resets body thermostat to a higher temperature = fever
24
Q

What is LAL assay?

A

Limulus amoebocyte lysate assay

25
Q

What is the LAL assay used for?

A

The detection of endotoxins, as they can contaminate materials and equipment in labs long after cell death.
LAL works by using WBC’s from horse show crab = limulus, when these WBC’s are mixed with endotoxins that form a cloudy substance different to human WBC’s. The degree of turbidity measures endotoxin contamination

26
Q

What are plasmids and what are their role?

A

Plasmids are extrachromosomal double stranded DNA which is circular.
They carry the genes which determine pathogenicity in microbes.
This seen with E.coli fimbria on F plasmid - male plasmid and in S.aureus in the coagulase gene

27
Q

What are lysogeny and what is their role?

A

Lysogeny is when a bacteriophage is incorporates DNA into bacterial chromosome where is then known as a prophage. This incorporates new properties into the bacteria (new genes that get carried with phage DNA by general or specialised transduction) = lysogenic conversion.

28
Q

What are the 9 cyopathic effects of viruses?

A
  1. Halt macromolcular synthesis in host cell
  2. Cause host cell to release lysosome contents
  3. Cause inclusion bodies to form on host cells
  4. Fusion of infected cells to form syncitium
  5. Changes in host cell function
  6. Induce host cells to produce interferons
  7. Cause antigenic changes on host cell surface
  8. Induce chromosomal changes in host cell
  9. Loss of contact inhibition in host cell
29
Q

What are fungal symptom causes?

A

Fungal waste products = symptoms

Chronic infections = allergic reactions

30
Q

What are the portals of exit?

A
  1. Respiratory tract - coughing and sneezing
  2. GIT - faeces and saliva
  3. Genitourinary tract - urine and vaginal secretion
  4. Skin
  5. Blood - biting anthropods and needles or syringes
31
Q

What is innate immunity?

A

Hosts have non-specific defence mechanisms.

32
Q

What is adaptive immunity?

A

Immune systems which have evolved - immunological memory. These are non-specific and specific, the specific are associated with memory.

33
Q

What are the differences between animal and plant immune mechanisms?

A

Plants dont have mobile/specialised immune cells
Physical barriers
Plants have innate type immune systems
Non-specific denfenses

34
Q

What are the roles of:

RBC’s, Neutrophils, Basophils, Eosinophils, Monocytes, T-cells and B-cells.

A 
RBC's - transports CO2 and O2
Neutrophils - phagocytosis 
Basophiles - Histamine 
Eosinophils - kills parasites 
Monocytes - phagocytosis 
T-cells - cell mediated immunity
B-cells - produce
35
Q

What are the different types of phagocytes?

A

Neutrophils, fixed and wandering macrophages.

36
Q

What is the process of phagocytosis?

A
  1. Chemotaxis and adherence of phagocyte to microbe
  2. Ingestion of microbe by phagocyte
  3. Formation of a phagosome
  4. Fusion of phagosome with lysosome to form a phagolysosome
  5. Digestion of ingested microbe by enzymes
  6. Formation of residual body containing indigestible material
  7. Discharge of waste materials
37
Q

What are microbial evasions to phagocytosis?

A
  1. Inhibit adherence which is done by either M-protein and capsules. This is seen in Strep. pyogenes and S.pneuminae
  2. Kill phagocytes which is done leukociains. This is seen in Staph. aurues
  3. Lyse phagocytes done by membrane attack complex. In Listeria monocytogenes.
  4. Escape phagosome which is in shigela and rickettsia
  5. Prevents phagosome and lysosome fusion which is in HIV and mycobacterium tuberculosis
  6. Survival in phagolysosome
38
Q

Define:

Susceptibilty, immunity, innate immunity and adaptive immunity.

A

Susceptibilty - lack of resistance to a disease
Immunity - ability to ward of disease
Innate immunity - defence against any pathogen
Adaptive immunity - defence resistance to specific pathogen

39
Q

What are physical factors of the body that try overcome microbes?

A
  • mucous membranes
  • skin has tightly pack keratin which is a protective protein
  • ciliary escalator which transports microbes in the mucous away from lungs
  • mucus traps microbes
  • saliva washes microbes off
  • vagina secretions which flow microbes out
  • urine flows them out
  • lacrimal apparatus which washed eyes out
40
Q

What are the chemical factors defence factors?

A

Sebum which is fungistatic
low skin pH (3-5)
lysosomes in tears, perspiration, saliva and urine
gastric juices which has a low pH (1.2-3)
Vaginal secretions have low pH (3-5)

41
Q

What is the first line of defence?

A
  • Intact skin
  • Mucous membranes
  • Normal microbiota
42
Q

What is the second line of defence?

A
  • Phagocytes (neutrophils, eosinophils, dendritic cells and macrophages)
  • Inflammation
  • Fever
  • Antimicrobial substance
43
Q

What is the third line of defence?

A
  • Specialised lymphocytes
  • T and B cells
  • Antibodies

Microbiology (10 decks)

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