Major Gram-Negative Bacterial Pathogens

Question 1

Histological appearance of gram -ve

Answer 1

Pink

Has periplasmic space layer

Question 2

Gram -ve characteristics

H-antigen - allows for?

K antigen -

O-antigen -

Answer 2

Gram -ve cell surface antigens
Two membranes
Thin PG layer and periplasmic space
Do not retain gram stain

e.g H-antigen
Flagellum
Motility on the bug and is a major virulence factor

Capsule

Outer membrane lipopolysaccharide

Question 3

Gram -ve cell envelope - nature of antigens

Outer membrane contains

Inner membrane contains?

Answer 3

Extend from surface whilst still being attached

Many lipoproteins which link OM to peptidoglycan layer

Transport proteins
Components of bacterial respiratory chain

Question 4

LPS O-antigens

Capsule role

Answer 4

Deter MACs to promote longevity of cell

Capsule can evade antibody binding

Question 5

Neisseria
Type

Seen where

Answer 5

Saprophyticus
Gram -ve diplococci

Plasma membrane of infected individuals

Question 6

Neisseria spp pathogens

1

2

What do they cause

What do they infect

Carriage and transmission

Tested for by

Answer 6

1. n. meningitidis (meningococcus)
   - meningitis, meningococcal septicaemia
   - infection of CSF and meninges
   - commensal carriage in nasopharynx
   - capsular
2. N. gonorrhoeae (gonococcus)
   - gonorrhoea
   - STI, oral and genital infection
   - neonatal transfer
   - sialylated capsule

Kovac’s oxidase test

Question 7

Meningitis is…

Symptoms

Signs

SEVERE

Answer 7

Inflammation of the meninges
Intense headache, fever, malaise, photophobia, stiff muscles
Loads of neutrophils in CSF –> lumbar puncture

Meningococcal SEPTICAEMIA

Question 8

N meningitidis

Carriage

Classification

Pathogenesis

• spread to?
• resistance?
• first infection leads to?
• protective factor?

Epidemiology

Answer 8

10-25% commensal carriage rate

5 serogroups depending on capsular antigen

Serogroup B in UK

Subarachnoid space or into blood via nasopharyngeal mucosa
IgA protease for serum resistance
Antibody production
Bactericidal antibody against capsule

Outbreaks in winter
2/3 cases occur in first 5 years

Question 9

Meningitis diagnosis and Tx

Answer 9

Presence of diplococci in CSF
Blood culture e.g oxidase tests - +ve

Penicillin, cefotaxime (chloramphenicol)
Rifampicin –> corticosteroids

Question 10

Haemophilus influenzae

Type of bacterium

Causes

Answer 10

Coccobacillus 
Non-invasive 
Otitis media, sinusitis 
Septicaemia, pneumonia and meningitis 
Penetrates submucosa of nasopharynx 
15-35% survivors have disability

Question 11

H. influenzae pathogenesis

How many capsular types

Carried how

Other pathogenic factors

Uncontrolled growth leads to

Answer 11

6 types
Capsule is main virulence factor –> type B 99%

Commensal carriage

Fimbriae and IgA proteases

Inflammatory response and septic shock

Question 12

H. influenzae epidemiology

Deaths/year

More common in….

Vaccine

Answer 12

350k-400k per year

Pneumonia in 3rd world
Meningitis in winter

Hib in 1992 - 3 doses

Question 13

Diagnosis and Treatment

Factor X
Factor V

Meningitis

Meds

Answer 13

Sputum, throat swabs, blood culture
Haemophili need factor X OR V for growth

Haemin
NAD/NADH

Antigen detection via PCR

Cefotaxime
Amoxycillin for noninvasive disease
Chemoprophylaxis for contacts - rifampicin