Bacterial Strategies For Host Colonisation Flashcards
Sites of vulnerability/ routes of entry
Respiratory tract
Intestinal tract
Urogenital tract
Conjunctiva
Physical removal strategies
Coughing/sneezing
Vomiting and diarrhoea
Urination
Tear production
Attributes invoked in effective host colonisation
Adhere to host cells + Resist physical removal
Invade host cells
Compete for iron + other nutrients
Evade the immune system
What are virulence factors
Virulence factors are molecular or cellular components produced by pathogens, such as bacteria, viruses, fungi, or parasites, that contribute to their ability to cause disease in a host organism. These factors can be categorized into different types based on their functions, such as:
Adhesion factors: These are proteins or other molecules on the surface of a pathogen that allow it to attach to host cells, tissues or extracellular matrix. Examples include fimbriae, pili, adhesins, and capsules.
Invasion factors: These are factors that allow pathogens to enter and survive within host cells. Examples include bacterial toxins, enzymes, and proteins that alter host cell membrane permeability.
Toxins: These are molecules produced by pathogens that damage host cells or tissues, and contribute to the symptoms of disease. Examples include exotoxins, endotoxins, and cytotoxins.
Immune evasion factors: These are molecules that help pathogens avoid detection and destruction by the host immune system. Examples include bacterial capsules and surface proteins that mimic host molecules.
Nutrient acquisition factors: These are molecules that allow pathogens to obtain nutrients from the host, such as iron or other essential nutrients. Examples include siderophores and proteases.
Pili function
Promote attachment + resistance to physical removal
- Pili are generally found in gram-negative bacteria
- Made up of protein called pilin
- Pili bind to sugar receptors in surface of eukaryotes
- Can colonise gut + urinary tract
- can be considered an adhesion
How do gram positive cells typically adhere to host cells and resist removal
They have proteins (adhesins) on their cell wall that binds to specific receptors on epithelial cells
How does Streptococcus pyogenes ( a gram positive bacteria ) bind to host cell
- causes throat infection
Protein F on bacteria binds to fibronectin on epithelial cells - Fibronectin is part of the host cells cytoskeleton
- Lipid teichoic acid also binds to fibronectin
- M protein also functions as adhesin
How does flagella/motility of Helicobacter pylori (a gram - bacteria) help colonisation at mucosal surfaces
-causes gut infections
-associated with stomach ulcers and cancers
-colonises the gut
- flagella allow it to love against the peristaltic action of the gut
- urease is produced in the bacterias cytosol and it produces ammonia from urea
The ammonia that’s produced is passed into the periplasmic space of the bacteria - this buffers the bacteria against the low ph of the gut
What are invasins
Molecules that activate the host cells cytoskeleton and promote cell entry by phagocytosis
In doing this they facilitate the growth and spread of the pathogen
Why do bacteria want to be in host cell
Host cell provides bacteria with ready supply of nutrients
Protects the bacteria from complement, antibodies and other body defence mechanisms
What are bacterial secretion systems
Bacterial secretion systems are specialized molecular machines that enable bacteria to transport proteins and other molecules across their cell membranes. These systems are critical for bacterial survival, as they allow bacteria to interact with their environment, acquire nutrients, and establish infections.
Explain the differences between the 6 different type of systems
Type I: This system involves the one-step secretion of proteins directly from the cytoplasm of the bacterial cell to the extracellular space.
Type II: This system involves a two-step process, with proteins first being translocated across the inner membrane and then across the outer membrane via a protein complex called the “secretin”.
Type III: This system involves the direct injection of proteins into host cells by pathogenic bacteria. This allows the bacteria to manipulate host cell functions and establish infection.
Type IV: This system can transport a wide variety of substrates, including proteins, DNA, and even entire bacterial cells. It is involved in processes such as conjugation, the transfer of genetic material between bacteria.
Type V: This system involves the secretion of proteins across both the inner and outer bacterial membranes via a β-barrel pore-forming protein.
Type VI: This system involves a needle-like apparatus that can inject proteins directly into other bacterial cells, promoting competition between bacteria.
What type of bacterial secretion system is most common in gram negative bacteria
Type 3
How do type 3 secretion all system work
The central component of the T3SS is a needle-like structure that extends from the bacterial surface and penetrates the host cell membrane.
To deliver proteins into host cells, the T3SS first recognizes a target cell and forms a close association with its surface. The needle then makes contact with the host cell membrane and creates a pore through which the proteins can pass. The proteins are then translocated across the pore and into the host cell, where they can interact with host cell components and manipulate cell functions.
The specific proteins injected by the T3SS vary depending on the bacterial species and the host cell type being infected. Some T3SS effectors can disrupt host cell signaling pathways, inhibit host immune responses, or promote bacterial survival and replication within the host.
What are the specific proteins injected by secretion systems called
Effector molecules
