Microbiology

Question 1

Three Manifestations of CNS infections?

Answer 1

Meningitis - crossed Blood-CSF barrier –> inflamed meninges.
Encephalitis: infection of brain parenchyma -> crossed BBB.
Abscesses: similar organisms to chronic meningtitis eg TB, Syphilis, Toxoplasmosis.

Question 2

Viruses that generally cause Meningitis?

Answer 2

Enteroviruses: echo, coxackie, Polio
Herpes (HSV, CMV, VZV)
Mumps
Japanese encephalitis
Rabies

Question 3

Three most common bacterial causes of Meningitis in Neonates?

Answer 3

E.coli/Other gram neg
Group B Strep
Listeria Monocytogenes

Question 4

Three most common bacterial causes of Meningitis if > 3 months

Answer 4

Neissenia Meningitidis
Streptococcus pneumonia
Haemophilus influenzae type B

Question 5

How would you distinguish a bacterial v viral infection of CSF via lumbar puncture sample?

Answer 5

Both will have raised pressure (bacteria) more so
Bacterial may be cloudy, viral won’t be
Glucose will be dramatically lower in bacterial
Protein will be higher in bacterial infection
Bacterial = polymorph cells Viral = lymphocytes

Question 6

In a neonate with signs of meningeal irritation what organism is most likely to be the cause if these are found on gram stain:
1. Gram Negative Rod
2. Gram Positive Cocci, Bacitracin Resistance and Growth on Mac, catalase negative.
3. Gram Postive coccobacillus
What should you treat with?

Answer 6

1. E.coli or even Klebsiella
2. Group B Strep
3. Listeria Monocytogenes

3rd Gen Cephalosporin + Penicillin (Group B Strep) + Genatmicin (Listeria)

Question 7

In an adult or child with sings of meningeal irritation what organism is most likely to be the cause if these are found on gram stain:

1. Gram negative Dipliococci
2. Gram Positive Cocci alpha haemolysis, catalse ngative, Sensitive optochin disc.
3. Gram Negative Coccobacilus, pleomorphic, grow CHA only need factor X and V, unvacinated

Answer 7

1. Neisseria Meningitidis
2. Streptococcus pneumonia
3. Haemophilus influenzae type B (

Question 8

Explain how a conjugate vaccine works?

Answer 8

Link polysaccharide from capsule to carrier protein = conjugate. The B-cells respond to polysaccharide antigen, and take up the protein marker and present it on MHC II. CD4+ T-cells are also able to respond to the carrier protein being presented to them by APC cells (eg DCs MHC II/TCR and CD80/CD28), become activated CD4+ cell. This T-cell then expresses CD40L able to interact with Activated B-cell and give the 3 signals (cytokines, CD40/CD40L, MHC II/TCR). Enables B-cell Affinity maturation, isotype swithcing and memory B-cells.

Question 9

What does alpha heamolysis look like?

Answer 9

Green product around colonies.

Question 10

What does beta heamolysis look like?

Answer 10

Clear around the colonies and cell plates

Question 11

Increased risk factors for Group B Strep (agalactiae) Meningitis for neonates? Prevention?

Answer 11

25% of mothers are carriers in birth canal
prolonged labour, pre-mature, fever during labour.
Should test and treat mothers.

Question 12

Most common cause of Encepalitis?

How would you treat?

Answer 12

Almost always viral, often HSV esp HSV1.

Aciclovir is good a reducing complications

Question 13

What viruses that effect the CNS do we have vaccine for?

Answer 13

Polio, Haemophilus influenza Group B, N. meningitidis C (meningocccol C, Streptococcus Pneumonia (protein conjugate), Rabies, VZV.

Question 14

Common cause of Fungal Meningitis?

Answer 14

Cryptococus

Treatment: Amphotericin B & Fluctosine

Question 15

Protozoal meningitis?

Answer 15

Naegleria (Chronic granulomatous inflammation

Question 16

Neuroinvasive vs Neurovirulent?

Answer 16

Invasive = ability to enter CNS
Virulent = how often it causes disease once in CNS

Question 17

What is an infection of the spinal chord called?

Answer 17

Myelitis

Question 18

What type of neuronal spread allows entry into the CNS

Answer 18

Retrograde Spread. Axon terminals to Cell Body. (slower but more deadly).