Bacterial Pathogenesis Flashcards
What is pathogenesis?
How a disease begins or develops
Why does pathogenesis occur?
It occurs as a consequence of complex interactions between an infecting pathogen and the host immune system
What is pathogenicity?
The ability of a pathogenic agent to cause disease
Who were the postulates formulated by and when?
Robert Koch & Friedrich Loafer in 1884
How is the pathogen capable of causing disease?
Point of entry
Evasion & Survival
Adherence & attachment
Colonisation at the site of adherence
Disease symptoms caused by bacterial toxins or invasion
What are the entry portals for a pathogen?
Respiratory
Skin
GIT
Genital
What are examples of pathogens that enter through the respiratory system?
Mycobacterium tuberculosis
Streptococcus pneumoniae
Haemophilus influenza
What is an example of pathogen that enters through the skin?
Clostridium tetani
Where do these pathogens enter the organism from?
Salmonella
Vibrio Cholera
Shigella dysenteriae
GIT
Which pathogen enters through the genitals?
Neisseria gonorrhoeae
Are entry portals specific or not?
Yes, the pathogen needs to enter through the specific portal in order to cause the disease otherwise there is no disease
Which processes help the pathogen to evade and survive?
Inhibition of phagocytosis
Modulation of surface structure to avoid recognition
Secretion of toxins that modulate the cell death pathways which causes apoptosis
What are the ways in which pathogens modulate their surface to avoid recognition?
Complement inhibition
Antigenic variability
Which staphylococcus-related protein decreases phagocytosis?
Staphylococcus aureus Protein A
How does SpA decrease phagocytosis?
It can affect the antibodies specifically or the source (B-cells) themselves
How does SpA affect antibodies?
Attache to antibodies,
Antibodies cannot perform their action
Antibody sequestered
Decreased phagocytosis
How does SpA affect the source?
Attaches to B cells
It acts as a superantigen toxin
Binds to the B cells through certain binding domains
It causes B-cell apoptosis
No adapted immune response
Decreased phagocytosis
What does factor H do?
Tessera meningitidis factor H binding protein evades complement-mediated phagocytosis
How does factor H work?
fHBP scavenges Factor H, which inactivates C3b
What is the effect of Factor H?
Minimizing complement activation and enhancing the survival of pathogen
What are the different bacterial adherence factors?
Adhesin
Capsule
Lipopolysaccharides (LPS) Technoic acids and lipoteichoic acids (LTA)
Fimbriae
Pilli
What is colonisation?
Establishment and growth of a microorganism on body surface
What are the stages of colonisation?
- Enter lumen of new host, pass through mucus
- Bind epithelial surface via host surface carbohydrates and protein
- Obtain nutrients from host
- Evade host cellular and humoral immunity
- Exploit inflammation to exit or invade host
What is virulence?
The degree of pathogenicity of a particular organism and the extent of damage that an organism cause to the host
How is bacterial virulence measured?
By calculating the number of bacteria required to cause the disease
On a graph which line would have the higher virulence?
The one that reached 50% of animals infected faster
What is infective dose 50?
The number of bacteria needed to infect 50% of the animals (host) exposed to them
What is lethal dose 50?
The number of bacteria needed to kill 50% of the animals (host) exposed to them
