Microbiology - NH Flashcards
(30 cards)
What is a bacterial pathogen of the upper respiratory tract? What disease(s) does it cause?
L15
Streptococcus pneumoniae
- causes sinusitis and Otitis media (OM)
What are the virulence factors of Streptococcus pneumoniae?
L15
- alpha-haemolytic: partial lysis RBC
- capsule: prevents complement activation
- cell wall adhesins: endothelial cell adhesion
- pneumolysin: cytolytic and cytotoxic
- autolysin: self-destruct protein
- neuroamidase: expose receptors for adhesion
- IgA1 protease: cleaves IgA antibodies + evades mucosal immune system
- hydrogen peroxide: toxic to cells
- competence: ability to take up DNA + antigenic variants
How is alpha-haemolysis a virulent factor of S. pneumoniae?
L15
- partially lyses RBC
Why is the capsule a virulent factor for S. pneumoniae?
L15
- prevents activation of complement cascade
- low antigenicity
Why are cell wall adhesins a virulent factor of S. pneumoniae?
L15
- endothelial cell adhesion
Why is pneumolysin a virulent factor of S. pneumoniae?
L15
- cytolytic and cytotoxic exoprotein
- binds Fc portion of antibodies
Why is autolysin a virulent factor of S. pneumoniae?
L15
- self-destruct protein
- releases cell contents
- i.e. more toxins
Why is neuramidase a virulent factor of S. pneumoniae?
L15
- expose receptors for adhesion
Why is IgA1 protease a virulent factor of S. pneumoniae?
L15
- cleaves secretory IgA antibodies
- evades mucosal immunity
why is competence a virulent factor of S. pneumoniae?
L15
- ability to take up DNA from environment
- modify genetic structure = antigenic variants of the capsule
i. e. change surface proteins to evade immune response
Why is hydrogen peroxide a virulent factor of S. pneumoniae?
L15
- toxic to cells
What types of virulence factors allow a microbe to be a successful pathogen?
L15
- ability to adhere to and colonise the host
- adapt to the environmental changes within the host
- avoid host defence system
- be able to defeat the host defence system
What are the virulence factors of Mycobacterium tuberculosis? Why do they contribute to pathogenicity of M.tb?
L16
- mycolic acid (waxy layer) on cell wall: resists desiccation
- grows slowly: common antibiotics (penicillin) are ineffective
- resistant to lysis agents: can grow inside phagocytes
- produce cord factor: increase survival within the host
Why is mycolic acid a virulent factor of M.tb?
L16
it is a waxy layer on the cell wall and enables resistance to desiccation
Why is slow growth a virulent factor of M.tb?
L16
means that common antibiotics (penicillin) are ineffective
Why is resistance to lysis agents a virulent factor of M.tb?
L16
- enables bacteria to grow inside the phagocytes
Why does production of cord factor contribute to the virulence of M.tb?
L16
- increases the survival of the bacteria in the host
- strains that do not produce cord factor are less virulent
What infections does Staphylococcus aureus cause?
L17
- folliculitis
- scalded skin syndrome
What are the virulence factors of S. aureus and what do they do?
L17
enzymes:
- coagulase: clots blood
- hyaluronidase: breaks down hyaluronic acid
- staphylokinase: breaks down blood clots
- lipases: break down lipids
- beta-lactamase: destroys beta-lactam antibiotics (penicillin)
anti-phagocytic defences:
- polysaccharide slime layer (capsule): prevents phagocytosis + enables adherence
- protein A: binds to antibody stems = prevents phagocytosis + complement activation
toxins:
- cytolytic toxin: disrupts cell membranes
- leukocidin: kills leukocytes (WBC)
- exfoliative toxin: breaks down desmosomes
- Toxic Shock Syndrome toxin: superantigen
How does coagulase contribute to the virulence of Staphylococcus aureus?
L17
- clots blood
- camouflages from phagocytes
How does hyaluronidase contribute to the pathogenicity of S. aureus?
L17
- degrades hyaluronic acid
- hyaluronic acid is a major component of cell-cell matrix
- allows bacterium to spread
How is staphylokinase a virulent factor of S. aureus?
L17
- breaks down blood clots
- allows rapid spread through damaged tissue
How do lipases contribute to the virulence of S. aureus?
L17
- break down lipases
- allows growth in sebum
- in sebaceous glands, hair follicles
How does beta-lactamase contribute to the virulence of S. aureus?
L17
- destroys beta-lactam antibiotics
- penicillin
