Gram Negative Bacteria

Question 1

Structure of gram negative?

How does it evade immune system?

Answer 1

Two membrane - outer membrane connected LPS layer
Outer layer - major LSP antigen
LPS and capsule help immune evasion

Question 2

What are the surface antigens?

Answer 2

KOH P 
K antigen - capsule
O antigen - outer membrane lipopolysaccharide
H antigen - flagellum 
Peptidoglycan

Question 3

Structure cell envelope - outside in?

Answer 3

Capsule –> LPS –> porin –> OM –> periplasm –> peptidoglycan –> inner membrane

Question 4

Give example of medically important gram negative spp

Answer 4

Neisseria - meningitis and gonnorhoea
Haemophilius Influenza - meningitis and pneumonia
Pseudomonas aeruginosa - burn pt and lung infection CF pt

Question 5

What is neisseria? - how do they grown and what would you culture them on?

Answer 5

Gram negative diplococci

Grow fastidiously on chocolate agar

Question 6

What is N. Meningitidis

Answer 6

Infection of CSF and meninges caused by commensal carry in nasopharynx
Capsular

Question 7

What is N. Gonnorhoea

Answer 7

STI, genital and oral infection

Lipooligosaccharide capsule often sialyated

Question 8

Explain serogrouping on N. Meningitis

Which serogroup comprised 90% diagnosis?

Answer 8

Dependent on polysaccharide capsular antigen
Serotype: A, B, C, Y, W135
Serotype B = 90% cases

Question 9

Pathogenesis of N. Meningitis

Answer 9

Spread to subarachnoid space or via nasopharyngeal mucosa to blood
IgA proteases for serum resistance

Question 10

Where is highest occurrence of meningitis

Answer 10

Sub-saharan Africa in ‘meningitis belt’

Question 11

Diagnosis meningitis?

Answer 11

CSF - many PMNLs and presence of bacteria
Blood culture (choc agar) - sugar fermentation test - +ve glucose and maltose, oxidase positive

Question 12

Tx meningitis?

Answer 12

Penicillin and cefotaxime

Followed by eradicative tx or rifampicin or ciprofloxacin (often w/ corticosteroid)

Question 13

What is haemophilus influenza?

Answer 13

Gram -ve cocco-bacilli

Question 14

Pathogenesis of h. influenza and main virulence factor?

Answer 14

6 capsular type - a–>f

Avoidance c3b binding, IgA proteases, fimbriae adhesion

Question 15

Diagnosis h. influenza?

Answer 15

Sputum, throat swab, blood culture (choc agar)

Haemophili require factor X (haemin) and factor V (NAD/ NADH) growth

Question 16

Tx h.influenza

Answer 16

Cefotaxime

Chemoprophylaxis for contacts - rifampicin

Question 17

What is pseudomonas aeruginosa?

Answer 17

Gram -ve motile aerobic rod

Question 18

Characteristic diagnosis p.aeurginosa?

Answer 18

Green spreading colonies with grapes smell

Question 19

Virulence of pseudomonas aeruginosa?

Answer 19

Extracellular proteases which break down tissue

Question 20

Complication of pseudomonas aeruginosa?

Answer 20

Septicemia

Question 21

What are the ESKAPE pathogens

Answer 21

Most antibiotic resistant pathogens - highest risk in hospital and clinical setting

E (+ve) - enterococcus faecium 
S (+ve) - staph aureus 
K (-ve) -klebsiella pneumoniae 
A (-ve) - acinetobacter 
P (-ve) - pseudomonas
E (-ve) - enterobacter