Flashcards in Pathogens Host Defenses Deck (103)
What are pathogens?
Microorganisms capable of causing disease/damage to the host.
Do all strains of one species have the same ability to cause disease?
What is a pathogen usually identified by?
The set of virulence genes that it carries and expresses
What is virulence?
A measure of the ability to cause damage to the host
What 2 factors is virulence determined by?
What is invasiveness?
The ability of microorganisms to become established in the host, or overcome the host defenses and to spread in the tissues
What is toxigenicity?
the capacity of the microorganism to produce substances known as toxins that damage specific tissues of the host
What happens once a host is exposed to a pathogen? 5 steps
1. Adherence to skin or mucosa
2. Invasion through epithelium
3. Growth and colonization (production of virulence factors)
4. Toxicity or Invasiveness
5. Tissue damage, disease
What are the 5 different types of virulence factors that pathogens use to invade host tissues?
3. enzymes that destroy host tissues
5. Type 3 Secretion Systems (T3SS) and Type 4 Secretion Systems (T4SS)
What do adhesins promote?
Specific attachment to host cell surfaces
How many cell types is one adhesin normally able to attach to?
one or many
What are Fimbriae/Pili? What do they mediate?
Polymers that mediate loose attachment
What are Afimbrial adhesins?
(not filaments) mediate close attachment
In what 2 ways do capsules aid pathogens?
1. They prevent them from being destroyed by host immune cells (phagocytes)
2. They help them attach to host cells and to other bacteria
What are 2 essential virulence factors for some bacterial pathogens?
Streptococcus pneumonia, Haemophilus influenzae
What is epidermis?
The outer layer of skin
How do most pathogens infect humans?
They penetrate the epidermis by using breaches in the skin (wounds, surgery, catheter)
What happens when pathogens penetrate the mucosa?
They destroy the single-cell layer or invade the cells themselves
What is hyaluronidase? Function?
An extracellular enzyme that degrades hyaluronic acid
Which pathogens release hyaluronidase?
Staphylococci, streptococci, clostridia
What is hyaluronic acid?
A sticky polysaccharide that holds host cells together
What is collagen? Function?
An extracellular enzyme that degrades the protein collagen present in connective tissues (muscle, cartilage)
What is the function of lecithinase? Causes the lysis of what?
An extracellular enzyme that degrades lecithin (phosphatidylcholine) in cell membranes -- causes the lysis of RBCs and destroys tissue cells
What is gas gangrene?
The term used to describe the decay or death of an organ or tissue caused by lack of blood supply in wounds infected by anaerobic bacteria
What microorganism are present in gas gangrene? What do they do?
Clostridium perfringens. They break down tissue by gas production.
What type of microorganism are Clostridium perfringens?
What enzyme do Clostridium perfringens use to lyse host cells in gas gangrenes? What enzymes do they use to destroy the extracellular matrix?
What are hemolysins? What are the different types of hemolysins?
A substance in the blood that destroys RBCs and liberates hemoglobin.
What are two examples of hemolysin enzymes?