Virulence Flashcards
What are virulence factors?
Mechanisms the bacteria has that allow it to overcome the host’s defenses and multiply
What are the three main types of virulence factors?
- Adhesins
- Invasins
- Toxins (endotoxin and exotoxin)
What are the four main routes of entry for bacterial infections?
- Urogenital tract
- Digestive tract
- Respiratory tract
- Conjunctiva
True or False: Adherence to a eukaryotic cell or tissue surface requires both a receptor and a ligand
True
What is an adherence receptor?
A specific carbohydrate or peptide residue on the eukaryotic cell surface
What is a bacterial ligand?
A macromolecular component of the bacterial cell surface (also called an adhesin)
List three ways that bacterial adhesins provide specificity
- Tissue tropism (some bacteria have a preference for certain tissues over others, ex. UTEC = urinary tract)
- Species specificity (some bacteria only infect certain species of animals (ex. E. coli K-88 only occurs in pigs)
- Age specificity
The huge variety of disease we see is due to the many types of adhesins with receptors that are species or tissue specific
What are invasins?
Virulence factors that enable the internalization of the bacteria
What are Type III secretion systems? Which type of bacteria have these systems?
A type of ‘machinery’ that many Gram negative bacteria have that let them deliver effector proteins (a type of invasin)
What is secretion?
The delivery of effector proteins (invasins) into the extracellular environment
What is translocation?
The delivery of effector proteins (invasins) directly into the host
What is the goal of Type III secretion systems?
The main goal is to hijack the host’s cell signalling mechanisms
Name two examples of Type III Secretion system pathogenicity
- Enteropathogenic E. coli (EPEC) delivers a receptor for one of its own adhesins into host cell membrane
- Salmonella typhimurium delivers effectors (invasins) that manipulate the host’s actin cytoskeleton and uptakes it into vacuoles.
What are spreading factors?
Bacterial enzymes that affect the physical properties of tissue matrices and intercellular spaces (thereby promoting the entry/spread of the pathogen)
What is the function of hyaluronidase and what bacteria is it produced by?
Hyaluronidase is an invasin and spreading factor (an enzyme) that attacks the intracellular matrix of connective tissue by depolymerizing hyaluronic acid. It is produced by Streptococci, Staphylococci, and Clostridia.
Basically hyaluronidase allows bacteria to penetrate deeper into tissues.
What is the function of collagenase and what bacteria is it produced by?
Collagenase is an invasin and spreading factor (enzyme) that breaks down collagen, the framework of muscles, which facilitates gas gangrene. It is produced by Clostridium histolyticum and Clostridium perfringens.
What is the function of neuraminidase and what bacteria is it produced by?
Neuraminidase is an invasin (an enzyme) that degrades neuraminic acid (also called sialic acid) residue in mucin in the intestinal tract. It is produced by intestinal pathogens such as Vibrio cholerae and Shigella dysenteriae.
What is the function of streptokinase and staphylokinase, and what bacteria are they produced by?
Streptokinase (and staphylokinase) are invasins (kinase enzymes) that convert inactive plasminogen to plasmin which digests fibrin and prevents clotting of the blood. They are produced by Streptococci and Staphylococci, respectively
What are the three ways that bacteria can avoid the host’s innate immune system?
- Evading complement system
- Anti-phagocytic defenses
- Anti-microbial peptides
What are three ways that bacteria can evade the host’s innate complement system?
- Capsules
- Polysaccharide capsules can hide bacterial components
- Some bacterial capsules can inhibit formation of complement
- Lipopolysaccharides (LPS)
- Main target of complement on Gram-negative bacteria
- LPS modification by attachment of sialic acid residues to the LPS’s O antigen prevents effective MAC (membrane attack complex) killing
- Destruction of complement component
(Ex. Pseudomonas aeruginosa produces an extracellular elastase enzyme)
What are five ways that bacteria overcome the host’s phagocytic defenses?
- Avoid contact between phagocytic and microbial cell
- Avoid engulfment
- Stop phagosome formation
- Inhibition of phagosome-lysosome fusion
- Avoid killing and digestion
How do most bacteria avoid phagocyte engulfment?
They have anti-phagocytic substances on the bacterial surface
How does Staphylococcus aureus avoid contact with the phagosome?
Staphylococcus aureus has cell-bound coagulase which clots fibrin on the bacterial surface and hides its antigenic surface
How does Staphylococcus aureus avoid engulfment by the phagosome?
Staphylococcus aureus has cell-bound or soluble Protein A (Protein A can interfere with the recognition of bacteria by phagocytic cells, such as macrophages)
How does Mycobacterium tuberculosis avoid contact with the phagosome?
Mycobacterium tuberculosis can inhibit phagocyte chemotaxis because its known to inhibit leukocyte migration
How does Pseudomonas aeruginosa avoid contact with the phagosome?
It has ‘surface slime’ (type of polysaccharide)
Which three bacteria have capsules that help them avoid engulfment by the phagosome?
- Streptococcus pneumonia
- Klebsiella pneumoniae
- E. coli
How does E. coli avoid degradation by the phagosome?
E. coli has an O antigen on its LPS (since the host’s complement system is looking specifically for the LPS, if E. coli has an O antigen ‘hat’ on its LPS, it isn’t recognized hehe)
Which bacteria can inhibit phagosome-lysosome fusion?
- Salmonella
- Legionella
- Chlamydiae
- Mycobacterium avium paratuberculosis
Which bacteria can survive inside the phagolysosome?
- Bacillus anthracis
- Staphylococcus aureus
- Coxiella burnetii
Which bacteria can escape from the phagosome?
Rickettsias produce a phospholipase enzyme that lyses the phagosome membrane within thirty seconds of ingestion
What are two ways that bacteria can kill or damage phagocytes?
- Kill phagocyte before ingestion (ex. Hemolysins secreted by S. pyogenes, S. aureus and streptolysins secreted by Streptococcus)
- Kill phagocytes after ingestion (ex. Mycobacteria, Brucella, Listeria)
What are hemolysins? Which bacteria usually secrete these?
Extracellular enzymes secreted by many Gram-positive pathogens that lyse red blood cells
What are streptolysins?
An enzyme secreted by pathogenic streptococci
What is the differences between endotoxins and exotoxins?
Exotoxins are released from bacterial cells and may act at tissue sites removed from the site of bacterial growth.
Endotoxins are released from cells and may be transported by blood and lymph and cause cytotoxic effects at tissue sites remote from the original point of invasion or growth.
Which toxin causes pyoderma?
Staphylococcus pseudointermedius exfoliating toxin
What is the function of E. coli enterotoxin?
They activate ion and water pumps causing loss of fluid and electrolytes from cells
Where do E. coli enterotoxins bind?
They bind to and colonize microvilli of small intestine. This causes a functional lesion but no structural lesion
How does an endotoxin damage the host?
They generally cause reactions related to inflammation
When are endotoxins released?
They are released when the bacterial cell is disrupted or destroyed, such as during bacterial replication or when the bacteria dies
