strep pneumoniae

characteristics

gram pos cocci, usually diplococci, non motile, non spore forming, catalase neg

growth and culture

fastidious, grow on blood agar, enriched media required for growth (source of catalase), alpha haemolytic (greening on agar), faculative anaerobe, 5% co2 for growth

colony morphology

draughtsman - lowered centre, raised edge due to autolysin lytA, can also be mucoid, small, dry, rough (unencapsulated)

optochin susceptibility test

sensitive to optochin - on blood agar plate w bacteria, zone of inhibition

bile solubility test

s. pneumoniae are soluble in bile, bile salts activate lytA and cause autolysis, diff s.pneumoniae from other a-haemolytic streptococci - clearing

moderate s.pneumoniae symptoms

sinustis, conjunctivitis, pnemonia complications i.e. lung abscess and empyemea, endocarditis

invasive pnemuococcal disease

in sterile site - bacteraemia, meningitis, endocarditis, septic arthiritis

clinical presentation of pneumonia

acute inflammation of lungs, cough, sob, pleuritic chest pain, fever, chills, malaise, anorexia

classification of causes of pneumonia

community aquired or hospital aquired

long lasting complications of pneumococcal disease

permanent hearing loss, seizures, cognitive impairment, increased risk of cardiac event/ heart attack

molecular mechanisms of pneumococcal colonisation of the host

to survive in nasopharnynx - must make contact w epithelial receptors, block complement system deposition, avoid/ degrade mucus and evade mucociliary clearage, impair neut activity

s. pneumoniae capsule

polysaccharide capsule that marks cell wall structures from phag and complement binding, in carriage reduced expression that reveals adhesins, in disease upregulated expression that allows survival

s.pneumoniae autolysin lytA causes

autolysins produced by bacteria in stationary phase induce cell death, releasing cell wall components that also trigger the complement cascade

tissue damage via pneumolysin

pore forming toxin, triggers comp cascade and highly pro inf

tissue damage via h202

catalase neg, causes local tissue damage, secreted by pneumolysin

tissue damage via inflammation induced by complement

strong inf response = most damage to host

pneumolysin release

released by autolysin

specimens used for lab identification

CSF/ blood - grown on HBA and CBA

s.p on hba

gray, dotted colonies

s.p. on cba

yellow cloudy colonies

gram stain

gram pos diplococci

bile salts can lyse…

the pneumococcal cell wall but not other alpha haemolytic streptococci - activates lyt a

common method in most hic labs

maldi-tof - in minutes

serotyping methods for identification

pcr targeting lytA, dna microarray, wgs

disadvantages of molecular testing

no isolate, wont always correlate w phenotype

serotype testing

latex agglunation, clumping

latex agglunation

ab to each capsule type bound to latex beads

clumping

pos result for antisera

issues w swabs in penumonia identification

cannot tell difference between normal MB and infection

lobar pneuomnia

right upper lobe infected

non lobar pneumonia

diffuse and wide spread

radiological identification of pneumonia

NOT DIAGNOSTIC

pneumococcal ag test

rapid lateral flow test, cell wall surface polysaccharide ag, urine or csf - false negs, ONLY CAN BE USED IN ADULTS

first line antibiotics

b-lactam ab

second line antibiotics

cephalosporin, fluroquinolones

amr and meningitis

mic breakpoints are lower in meningitis, need to use more drugs

predispositions to lung infection

alterations in cough reflex, mucociliary elevator function

ideal pneumo vax

prophylactic and therapeutic

ab on mucosal surfaces

iga

ab in blood and meninges

igg

main ab secreted by plasma cell

igm

t independant antigen

b cell differentiates into only plasma b cells producing igm or igg2

t dependent antigen

t cell help allows formation of memory b cells and production of igg1 and igg3 by plasma cells

t cell help provides

isotype switching, high binding affinity, memory

what ag can t dependent cells recognise

protein ag

protein polysaccharide conjugate (ppc) vaccine

chemically connected protein ag and polysaccharide ag - t cell reacts w peptides from protein and provide help

what ag can t independent cells recognise

polysaccharide, lipids, nucleic acids

ppc vax

b cell recognises ps and internalises complex, breaks down protein and loads in mhc ii. t cell specific to protein can create help, b cell secretes ps specific ab.