Medical Microbiology & Clinical Pneumonia

Question 1

Breathlessness DDx

Answer 1

Left ventricular failure
Pulmonary oedema
Pleural effusion
Pneumonia

Question 2

What investigation would you do for a pleural effusion

Answer 2

Pleural tap (=thoracocentesis)

and then anaylse the fluid

Question 3

Causes of pleural effusion

Answer 3

Infection and malignancy

Question 4

What lab does the pleural fluid go to

Answer 4

Chemical, cytology and micro!

Question 5

Why would you send a sample of pleural fluid to clinical chemistry

Answer 5

To measure the amount of protein:

Transudate: protein < 30 g/dl
Exudate : protein > 30 g/dl

Question 6

What is transudate and cause

Answer 6

Low protein fluid
Caused by heart failure

(or renal or liver failure –> low protein)

Question 7

What is exudate and what is it caused by

Answer 7

High protein fluid
Caused by
Infection
Cancer

Question 8

What would micro do with a pleural fluid sample

Answer 8

Microscopy (gram staining)
Culture
Sensitivity

Question 9

What are the likley organisms in a pneumonia

Answer 9

Pneumococcus (strep pneumoniae)

Haemophilus influenzae

Question 10

Difference between gram +ve and gram -ve

Answer 10

Gram +ve has thick peptidoglycan (NAM+NAG) cell wall

Gram -ve has thin cell wall and 2 membranes

LPS prevents the uptake of a component of the gram stain in the gram -ve bacteria

They stain with a pink counter stain

Question 11

What shape is pneumococcus and haemophilus influenzae

Answer 11

Pneumococcus= gram +ve diplococcus

Haemophilus influenzae= gram -ve rods (actually more like cocci-bacilli as they are rounded rods)

Question 12

What antibiotic do you treat pneumococcus with

Answer 12

Benzyl penicillin

Question 13

How did pneumococcus become resistant to penicillin

Answer 13

Alters the protein that penicillin binds to

Question 14

Why wouldn’t you give coamoxiclav if you know it’s pneumococcus

Answer 14

Because if the pneumococcus is resistant to penicillin, this will be because it has altered the protein that the penicillin usually binds to, NOT because it has made an enzme that breaks down penicillin.

The clavulonic acid is a beta lactamase inhibitor, so it is pointless to use with pneumococcus because this is not targeting the correct method of resistant

Question 15

T/F if the pneumococcus becomes resistant to penicillin this usually occurs rapidly and is hard to overcome with higher doses of penicillin

Answer 15

F.
if the pneumococcus becomes resistant to penicillin this usually occurs gradually and is usually overcome with higher doses of penicillin

Question 16

Where in the body can penicillin resistant pneumococcus not be overcome with higher doses of penicillin?

Answer 16

In the case of meningitis.

Where as in the lungs you can overcome pneumococcus resistance by adding more Abs,

There is a risk that not enough of the beta lactam antibiotic will get into the CNS. Whereas with the lungs you know the beta lactam will get there easily, the same cannot be said for pneumococcal infections in the brain

Question 17

What will you treat haemophilus influenza with

Answer 17

Treat with amoxicillin

Question 18

Which bug is more likely to become resistant to Abx: pneumococcus or haemophilus influenzae

Answer 18

Haemophilus influenzae

Question 19

What is the mechanism of action of resistance for haemophilus influenzae

Answer 19

It becomes resistant to amoxicillin as it produces beta lactamase

Question 20

How can the resistance of haemophilus influenzae be targeted

Answer 20

Give co-amoxiclav. The clavulonic acid here will inhibits the beta lactamase produced by the bacteria

Question 21

Single best investigation when you suspect a pleural effusion

Answer 21

chest x-ray

Question 22

What are the 3 causes of transudate

Answer 22

Heart failure

Liver failure (loss of protein)

Renal failure (proteinuria)

Question 23

How sensitive is the gram stain

Answer 23

The gram stain test isn’t very sensitive, so a negative gram stain doesn’t rule infection out

Question 24

How long does sensitivity testing take

Answer 24

48hr

Question 25

In which cases might you give ABx before taking culutres

Answer 25

Only in meningitis, severe sepsis or meningeal septicaemia