Gram Negative Bacteria Flashcards
Structure of gram negative?
How does it evade immune system?
Two membrane - outer membrane connected LPS layer
Outer layer - major LSP antigen
LPS and capsule help immune evasion
What are the surface antigens?
KOH P K antigen - capsule O antigen - outer membrane lipopolysaccharide H antigen - flagellum Peptidoglycan
Structure cell envelope - outside in?
Capsule –> LPS –> porin –> OM –> periplasm –> peptidoglycan –> inner membrane
Give example of medically important gram negative spp
Neisseria - meningitis and gonnorhoea
Haemophilius Influenza - meningitis and pneumonia
Pseudomonas aeruginosa - burn pt and lung infection CF pt
What is neisseria? - how do they grown and what would you culture them on?
Gram negative diplococci
Grow fastidiously on chocolate agar
What is N. Meningitidis
Infection of CSF and meninges caused by commensal carry in nasopharynx
Capsular
What is N. Gonnorhoea
STI, genital and oral infection
Lipooligosaccharide capsule often sialyated
Explain serogrouping on N. Meningitis
Which serogroup comprised 90% diagnosis?
Dependent on polysaccharide capsular antigen
Serotype: A, B, C, Y, W135
Serotype B = 90% cases
Pathogenesis of N. Meningitis
Spread to subarachnoid space or via nasopharyngeal mucosa to blood
IgA proteases for serum resistance
Where is highest occurrence of meningitis
Sub-saharan Africa in ‘meningitis belt’
Diagnosis meningitis?
CSF - many PMNLs and presence of bacteria Blood culture (choc agar) - sugar fermentation test - +ve glucose and maltose, oxidase positive
Tx meningitis?
Penicillin and cefotaxime
Followed by eradicative tx or rifampicin or ciprofloxacin (often w/ corticosteroid)
What is haemophilus influenza?
Gram -ve cocco-bacilli
Pathogenesis of h. influenza and main virulence factor?
6 capsular type - a–>f
Avoidance c3b binding, IgA proteases, fimbriae adhesion
Diagnosis h. influenza?
Sputum, throat swab, blood culture (choc agar)
Haemophili require factor X (haemin) and factor V (NAD/ NADH) growth