Bacterial Pathogenesis and Transmission Flashcards Preview

BMS212 - Bacteriology > Bacterial Pathogenesis and Transmission > Flashcards

Flashcards in Bacterial Pathogenesis and Transmission Deck (21)
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1
Q

5 ways pathogens are transmitted

A
  1. Airbourne
  2. Water & food
  3. Contact
  4. Vehicle (aka fomites)
  5. Vector (living transmitter such as insects)
2
Q

Epidemiology - definition

-6 factors that interact in the chain of infection

A
-is the study of factors that influence the frequency and distribution of infectious diseases
factors that interact in the chain of infection;
    -host susceptibility
    -means of entry
    -pathogenic microorganism
    -mode of transmission
    -means of escape
    -reservoir
3
Q

Process of infection (6 steps)

A
  1. Enter the host
  2. Adhere to cell surfaces
  3. Colonise cell surfaces
  4. invade tissues
  5. Evade host defenses
  6. Produce toxins and other harmful products
4
Q

Process of Infection;

-Entering the host -> ways it is achieved (5)

A
  • penetrate skin or mucous membranes
  • ingestion with food
  • inhalation in aerosols
  • sexual transmission
  • transmission on an object (fomites)

*pathogenic organisms have to enter the body

5
Q

Process of Infection;

-Adhesion to cell surfaces (2)

A

-Mechanisms;

  • Pili or fimbriae - organelles that project from the cell surface and attach to host cells
  • Adhesins - attachment molecules that permit the bacterium to adhere to receptors on the membranes of certain cells or tissues

*need to adhere otherwise bacteria will be washed/brushed off

6
Q

Process of Infection;

Colonise cell surfaces - why must colonise

-e.g.

A

*bacteria must colonise host tissues -> a single bacterium on its own will never cause any harm (need a population)

e. g. intestinal surface is continually replenished
- to est. an infection at such a site, need to adhere to epithelium and multiply before the mucus and extruded epithelial cells are swept away

Colonisation = when bacteria grow on and within host tissues

7
Q

Process of Infection;

Invasion of tissues

-Aggressins (2 e.g.)

A
  • Bacteria invade tissues using aggressins (enzymes from bacteria)
    • have proteolytic or lipolytic activity to assist bacteria in invading tissues and intercellular spaces

e.g. Neuraminidase degrades neuraminic acid (the intercellular cement of epithelial cells of the intestinal mucosa) -> vibrio cholerae and shigella dysenteriae

also, collagenase (produced by clostridium difficile) -> breaks down collagen which connect cells to form tissues

8
Q

Process of Infection;

Evasion of host defenses

A
  • Some pathogenic bacteria able to resist bactericidal components of host tissues
  • encapsulated strains are more virulent and resistant to phagocytosis (e.g. pneumococci)
  • some bacteria can survive inside phagocytic cells (i.e. legionella pneumophila, brucella abortus)
9
Q

Process of Infection;

Production of toxins (2 types)

-what toxins can do

A
  • Bacterial toxins are soluble substances that alter normal metabolism of host cells and damage host
    • are the key of pathogenicity
  • 2 types of toxins;
    1. Endotoxins: Lipid A of gram -ve cell wall toxin
    2. Exotoxins: Protein toxins
  • toxins may act on cells in number of ways (i.e. damage cell membranes or inhibit protein synthesis)
    • also can interfere with cell signalling, inhibit release of neurotransmitter and activate host immune responses
10
Q

Properties of endotoxins

  • what are they
  • what makes them toxic
  • when released by bacteria
A
  • they are; Lipopolysaccharides that are structural components of cell walls of gram neg. bacteria
  • Lipid A component is responsible for toxicity of endotoxin
  • is released from growing bacterial cells or from dead cells when they are lysed
11
Q

Actions of Endotoxins

  • comparison to exotoxins
  • what it can cause
A
  • Are less potent and less specific in their actions than exotoxins
  • are heat stable
  • effects on such wide variety of host cells result in host responses such as inflammation and fever than can cause gram-negative sepsis which leads to shock and death
12
Q

Properties of Exotoxins

A
  • denatured by heat, acid & proteolytic enzymes
  • have high biological activity
  • potent, have specific poisons
  • site of action is more localized and confined to particular cell types or cell receptors
  • among the most potenet per unit weight, of all toxic substances
13
Q

Categories of Exotoxins (3)

A
  • categories based on biological effect
    1. Neurotoxins: act on neurons & release of neurotransmitters -> interfere w/ muscle excitation & producing paralysis
    2. Cytotoxins: disrupts host cells - have a wide array of host cell specificities & toxic manifestations
    3. Enterotoxins: stimulate hypersecretion of water and electrolytes from intestinal epithelium and thus produce watery diarrhea.
14
Q

Vibrio cholerae toxin

-what toxin does

A
  • when toxin released from bacteria, binds to intestinal cell and triggers endocytosis of toxin
  • inside cytoplasm, the toxin A subunit activates the G protein to continually stimulate adenylate cyclase to produce cAMP
    • high cAMP levels activate cystic fibrosis transmembrane conductance regulator (CFTR) causing a dramatic efflux of Cl ions and water, leading to water diarrhea
15
Q

Botulinum toxin

-what it does and leads to

A
  • Botulism due to formation of potent exotoxins by large, spore-forming gram-positive bacterial rods
  • caused by the neurotoxins Clostridium botulinum
  • toxins block transmission of signal between nerves and muscles -> causes paralysis
16
Q

Types of Bacterial infections (5)

-3 things that determine the type of infection that develops

A
  1. Purulent infections
  2. Bacteraemic infections
  3. Toxaemic infections
  4. Granulomatous infections
  5. local infection
  • Type of infection that develops depends on properties of pathogen, methods of pathogen to infect & invade host and health or susceptibility of host
17
Q

Types of Bacterial Infections

  • Purulent (2 other names)
  • what is it
A
  • Produce pus at site of inflammation
  • formed from the accumulation of dead phagocytes, bacteria and host tissue
  • AKA suppurative, pyogenic or purulent
  • can be caused by many species part of normal skin flora if they enter through damaged skin

e.g. stahylococcal, streptococcal, corynebacterium

18
Q

Types of Bacterial Infections

Bacteraemic

e.g.

A
  • Occur when bacteria enter the blood stream
    • may occur following a wound, surgery or injection
  • may lead to septic shock

e.g. Staphylococcus aureus can infect wounds and cause blood poisoning

19
Q

Types of Bacterial Infections

Toxaemic

A
  • Bacterial toxins in blood (may be endo or exotoxic)
  • Toxins interfere w/ cellcular mechanisms and pathoways
  • is often fatal
20
Q

Types of Bacterial Infections

Granulomatous

e.g. of mycobacteria

A
  • Usually caused by slow growing, intracellular organisms
  • lesions become walled off due to host response

e. g. mycobacteria causing tuberculosis
- one feature of immune response is formation of a granuloma -> first acts to contain infection, but some bacilli survive inside granulomas for long time in dormant state

21
Q

Types of Bacterial Infections

Localised

e.g. salmonella enterica

A
  • bacteria that are adapated to infecting one site (i.e. gut, respiratory, urogenital or integument)
    e. g. salmonella enterica (is infection of gut)