Denise - Streptococcus Flashcards
How is streptococcus classified
(5)
Based on the haemolytic propertied of the organism e.g. Alpha haemolytic strep
Based on the presence of surface antigens determined by immunological assays
Based on biochemical reactions
Based on protein analysis
Based on genetic analysis
Classify step based on haemolysis
Alpha haemolytic strep
Beta haemolytic strep
Gamma/no haemolytic strep
How do we classify strep based on their serological groups, how is this done
Based on the Lancefield groups of streps
How do we group streps based on Lancefield groups?
(6)
C-substance polysaccharide in their cell walls
Antigenic differences
Easily extractable
Classified primarily Beta Haemolytic strep
GAS (Group A strep) and GBS (Group B strep) are the most clinically significant
S. pneumoniae and S. viridans (the alpha haemolytic streps) have no group specific antigen i.e. cannot be grouped based on lancefield groups
Which streps cannot be identified using lancefield groupings and why
S. pneumoniae and S. viridans (the alpha haemolytic streps) have no group specific antigen i.e. cannot be grouped based on lancefield groups
Write about S. pneumoniae
One of the 12 priority pathogens according to WHO
High burden of disease and rising rates of penicillin resistance
What type of resistance is seen in S. pneumoniae
Penicillin resistance
Why is S. pneumoniae listed as one of the 12 priority pathogens
High carriage rates
Genetic adaptability
Ability to shift from commensal to pathogenic interaction in its host
Write about the pathogenesis of S. Pneumonia
(3)
Colonisation is the prerequisite for both transmission to other individuals and invasive disease in the carrier
Carriers can shed S. pneumoniae in nasal secretions and thereby transmit the bacterium
Dissemination beyond its niche along the nasal epithelium, either by aspiration, bacteraemia or local spread
How does S. pneumonia spread from a carrier to another individual
Nasal secretions
How does S. pneumonia spread from the nasal epithelium to cause infection
Aspiration (bacteria into respiratory system)
Bacteraemia (bacteria in circulation)
Local spread (spread into tissues)
What infection is caused if there is aspiration of S. pneumonia
This will cause pneumonia in the lung
What infection is caused if there if S. pneumonia colonisation leads to bacteraemia
This will cause meningitis
This can occur directly from colonisation or can lead on from pneumonia
What does local spread of S. pneumonia from nasal epithelium lead to
Otitis media
What factors affect S. pneumonia shedding from nasal epithelium of carriers
(5)
Pneumolysin increases shedding
Capsule type and amount increases shedding
Viral co-infection increases shedding
Anticapsule IgG decreases shedding
Anticapsule IgA1 has no effect
How does pneumolysin increase shedding of S. pneumoniae?
(3)
Inflammation promotes secretion production by nasal epithelium
Bacteria present in mucus lining epithelium
Runny nose -> sneezing -> facilitates spread
How does capsule type and amount increase shedding?
(2)
Capsulated strains of S. pneumonia inhibit entrapment by mucin
S. pneumonia can escape the mucous produced by the S. pneumoniae
How can anticapsule IgG decrease Shedding?
IgG binds to bacteria
Agglutination blocks release
Bacteria can’t escape in mucous
Why does anticapsule IgA1 have no effect on S. pneumoniae
Bacterial protease relieves agglutination
Why does viral co-infection increase shedding of S. pneumoniae
Increases bacterial load and increases mucous production
Nasal epithelium infected with virus -> increases production of mucous
More bacteria present in mucous
Spread by runny nose etc
What are the two types of infections caused by S. pnuemonia
Non invasive
Invasive soft tissue infections
List the most common S. pneumonia non invasive infections
Acute bacterial pneumoniae
Otitis media
Write about acute bacterial pneumoniae caused by S. pneumoniae
(5)
Lower respiratory tract infection
Preceeded by viral infection
Community acquired infection Pneumonia CAP
Older adults
Seasonality - increased in winter months
Write about otitis media caused by S. pneumonia
Most common cause of middle ear infection in children