Medical Microbiology & Clinical Pneumonia Flashcards
Breathlessness DDx
Left ventricular failure
Pulmonary oedema
Pleural effusion
Pneumonia
What investigation would you do for a pleural effusion
Pleural tap (=thoracocentesis)
and then anaylse the fluid
Causes of pleural effusion
Infection and malignancy
What lab does the pleural fluid go to
Chemical, cytology and micro!
Why would you send a sample of pleural fluid to clinical chemistry
To measure the amount of protein:
Transudate: protein < 30 g/dl
Exudate : protein > 30 g/dl
What is transudate and cause
Low protein fluid
Caused by heart failure
(or renal or liver failure –> low protein)
What is exudate and what is it caused by
High protein fluid
Caused by
Infection
Cancer
What would micro do with a pleural fluid sample
Microscopy (gram staining)
Culture
Sensitivity
What are the likley organisms in a pneumonia
Pneumococcus (strep pneumoniae)
Haemophilus influenzae
Difference between gram +ve and gram -ve
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
What shape is pneumococcus and haemophilus influenzae
Pneumococcus= gram +ve diplococcus
Haemophilus influenzae= gram -ve rods (actually more like cocci-bacilli as they are rounded rods)
What antibiotic do you treat pneumococcus with
Benzyl penicillin
How did pneumococcus become resistant to penicillin
Alters the protein that penicillin binds to
Why wouldn’t you give coamoxiclav if you know it’s pneumococcus
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
T/F if the pneumococcus becomes resistant to penicillin this usually occurs rapidly and is hard to overcome with higher doses of penicillin
F.
if the pneumococcus becomes resistant to penicillin this usually occurs gradually and is usually overcome with higher doses of penicillin
Where in the body can penicillin resistant pneumococcus not be overcome with higher doses of penicillin?
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
What will you treat haemophilus influenza with
Treat with amoxicillin
Which bug is more likely to become resistant to Abx: pneumococcus or haemophilus influenzae
Haemophilus influenzae
What is the mechanism of action of resistance for haemophilus influenzae
It becomes resistant to amoxicillin as it produces beta lactamase
How can the resistance of haemophilus influenzae be targeted
Give co-amoxiclav. The clavulonic acid here will inhibits the beta lactamase produced by the bacteria
Single best investigation when you suspect a pleural effusion
chest x-ray
What are the 3 causes of transudate
Heart failure
Liver failure (loss of protein)
Renal failure (proteinuria)
How sensitive is the gram stain
The gram stain test isn’t very sensitive, so a negative gram stain doesn’t rule infection out
How long does sensitivity testing take
48hr
In which cases might you give ABx before taking culutres
Only in meningitis, severe sepsis or meningeal septicaemia
