Streptococcus infections Flashcards
are streptococci a gram-positive or negative organism? What does it mean and what does it stain and in what colour?
Gram positive organism, stain will bind the peptidoglycan on outside of cell wall (no outer lipid membrane). Will stain purple.
How does streptococcus characteristically grow?
in pairs or chains.
What initial tests would you do for strept?
check growth on blood agar (horse blood +gelatin) in aerobic and anaerobic conditions.
does strep gorw in aerobic or anaerobic conditions?
aerobically grows on blood agar.
What three classes are gien based on haemolysis?
alpha haemolytic- will lyse blood and will produce H202 which makes green methlyglobin.
beta hamolytic- will completely lyse blood via steptolycin (O and S) O is oxygen sensitive, S isnt’.
gamma haemolytic- may look like strep with stains, but no haemolysis
How can you further classify beta haemolytic strep?
Categoreised into lancefield groups based on carbodygrate antigen composition (A-G).
How are alpha haemolytic streps separated and what are they?
Distuished with opticon (antibiotic) disc differs on their sensitivity.
S. pneumoniae or from s. viridans group (e.g. s. aures) which are your traditional commesnals.
what are the A, B C and F strep belonging to the beta haemolytic group?
(A) s. pyogenes
b) s. agalactiae
c) s. dysgalactiae
f) s anginosus of milleri group.
how can s. pneumoniae and s. pyogenes be subdivided?
s. pneumoiae subidved based on seroptypes (polysaccharaies capsules).
s. pyogenes subdivided based on M protein genetic sequences.
What categories of virulence factors?
Those involved in: colonisation, invasion evasion devastation
What molecules help s.pneuominae colonise and bind to cells?
adhesins like Cbp-A binds to choline.
N-glycan degradation enzyme breaks down surface glycocalyx o allow cell access.
What determines whether s. pneumoniae is virulent or commensal?
The cell numbers.
If viral infection present, number for virulence drastically reduced.
How does s. pneuominae invade host?
traverse through the epithelium inside of vacuoles.
Rstrcition of colonies leads to lysis via autolysina nd penumolysin release.
What feature of s. penumoniae is most important virulence factor for their evasion?
capsule- ones without capsule do not cause disease.
Which s. pneumoniae proteins block complemnt?
pspA blocks C3 fixation.
pspC binds factor H to prevent C3b formation through the alternative pathway.
which s. pneumoniae protein resists oxidative ROS?
psaA
Which s. pneumoniae proteins break up IgA?
neuraminidases (removes secretory component), and also Ig1a protease (cleaves at hinge region)
What toxins for devastation does s. pneumoniae use?
pneumolysin release upon colony restrction/ phagocytosis.
H202 production.
Superantigens: F-antigen and C-polysaccharide will induce inflammatory response for dissemination into the blood.
What are the 9 diseases associated with s. pneumoniae infection?
otitis media (segun) , sinusitis (claudia), conjunctivitis, meningitis (sarahB) pneuomonia (Izzy B) empyema (anna), peritonitis (Han) osteomyleitis (Liz) speitci arthritis.
What is otitis media, sinitis and conjunctivitis inflammation of? (s. pneumoniae)
inflammation of the middle ear (can lead to burst eardrum and pus discharge).
inflammation of nasal mucosa (potential to spread into brain)
inflammation of the conjunctiva lining the inside of the eylid- eye redness and inflammation.
symptoms of meningitis (s. pneumoniae)
inflammation of meninges (surrounding CNS)
sensitivity to light, headache and neck stiffness.
Aggressive IV antibiotics requied/
What occurs during pneumonia and what are symptoms? (s. pneumoniae but also other strep)
fluid and pus fills up the air sacs along with inflammation. Coughing with phleg,/ pus and fever and chills.
Whats happens in empyema? (s. pneumoniae)
pus gathers in the pleural cavity.
fever chest pain and breathlessness.
severe cases require drainage and surgery (associated with 20% mortality)
What occurs in peritonitis? (s. pneumoniae)
inflammation of peritoneum that surround the abdominal cavity- fever, abdominal pain/ nausea and accumulation of fluids in the peritoneal cavity and renal dysfunction.
Can sometimes use lavage to wash out bacteria.
What are the molecules important for S. pyogenes adherence to epithelial and mucosal cells? (colonisiation)
M protein, lipoteich acid (LTA) (epithelial)
fibronectin binding protein (protein F) for mucosal cells.
S. pyogenes invasion is much more aggressive than S. pneumoniae, what three enzzymes are important in invasion?
streptokinase
streptodonases
hyaluronidase
proteases
What do streptokinases and streptodornases do in S. pyogenes infection?
lyses fibrin
The latter has Dnase and RNase activity
What do hyaluronidase and proteases do in S. pyogenes infection?
digests host connective tissues (and S. pyogenes own capsule)
protests cause soft tissue necorsis.
How does the M protein contribute to invasion and in S. pyogenes infection?
M proteins cause a local inflammatory reaction for the invasion of the blood stream.
How does the M protein contribute to evasion and in S. pyogenes infection?
1) M protein can bind host antigens (to pretend that it is ‘self’) and induced tolerance and immunosuppression/
2) negative charge interferes with phagocytosis and complement deposition.
How else is S pyogenes protected from drugs and the immune response, and from complement?
Forms a biofilm.
C5a peptidase will cleave C5
Spy|CEP cleaves human CXC chemokines.
What toxins in S pyogenes cause lysis and fever and rash (in scarlett fever)
Stretptolysin (punches pores)
Streptodronases are leukotoxic.
proteases cause soft tissue damage.
What happens in osteomyelitis?
inflammation of the bone tissue- bone destructi and necrosis.
Fever, loss of motion.
Prolonged antibiotics, surgery/amputation.
Describe septic arthritis
When the infection is within the synovial fluid. Causes pain, erythea swelling and fever.
Joint aspiration to treat and antibiotic treatment.
