Medical microbiology and clinical pneumonia Flashcards
ddx fo 55yr old women with breathlessness
PMH - known dm, SH - smoker 30/day
- LVF
- pul oedema
- pleural effusion
- pneumonia
Smoker – IHD
Dm – IHD
So LVF which presents as pul oedema (failure is the clinical feature, pul oedema is feature they might have)
Pleural effusion – from cancer secreting fluid
Pneumonia – dm makes you at risk because immunosuppressed
what do these examination findings suggest:
reduced expansion on R
reduced tactile vocal fremitus on R
percussion - dull at R base
auscultation - reduced breath sounds on R
R sided pleural effusion
- Not pneumonia because vocal resonance reduced –typical of fluid – if resonance increased = pneumonia – vibrates more and sounds louder
- Auscultation – louder breath sounds and bronchial breathing = pneumonia
- Pul oedema = symmetrical on both sides
- Pneumothorax = resonant percussion
pleural effusion
at top there is a fluid level - flat line
Ix for pleural effusion
pleural tap
send to all labs - clinical chemistry, cytology and microbiology
what do clinical chemistry do with a pleural tap
measure amount of protein in effusion
transudate: proten 30g/dl
- low protein fluid
- caused by HF - pressure drives the fluid into the lungs
exudate: protein >30g/dl
- high protein fluid
- caused by infection/cancer
what do microbiology do with pleural tap
microscopy, culture and sensitivity
microscopy is gram staining for the bacteria, confirm infection and guide treatment - likely organisms:
- pneumococcus (strep pneumoniae) (gram +ve)
- haemophilus influenzae - if smoker (gram -ve)
gram -ve more difficult to treat because of the outer membrane
Erythromycin act inside membrane on ribosome – cant get through the membrane In =-ve
penicillin will work on peptidoglycan cell wall - benzylpenicillin can’t get across the gram -ve membrane so need broad spectrum eg amoxicillin
Pairs of blue diplococci - Pneumococci slightly oblong like rugby balls – in keeping with pneumococcus
Gram +ve – thick wall so stain picked up in peptidoglycan wall
Haemophilus – coccobacilli – short rods – don’t take up the gram stain in the same way – have outer membrane adn dont have thick peptidoglycan cell wall
counter stain – stain the pink colour of the background but have definite shape
bacteria Don’t divide properly = elongated form when on AB
clue that on AB because effect how cell wall is formed in daughter cells
Mx of gram +ve diplococcus
for pneumococcus - benzylpenicillin
get mutations in penicillin binding protein - so dont bind penillin well - so use higher dose/amoxicillin
so community acquired 1st line rx is amoxicillin because also covers haemophilus
Mx of gram -ve rod
haemophilus influenzae - treat with amoxicillin
microbiology culture and sensitivity
grow the bacteria and see which AB kill (or prevent growth) - results come back after 48hr
done to check sensitivity
most reliable way of doing this is phenotypic testing
why do you need to send sample for culture before giving AB
AB can have enough activity to stop growing in vitro – so might get false -ve results so don’t give AB before cultures
Single colonies
Pneumococcus have a haemolysis.
Display autolysis 0- grow rapidly and then die – hole in middle of colony – drafts men colony
disk diffusion
Impregnanted disk on aga plate – amount of growth around the disk
Measure zone size
If zone >15mm sensitive
If <15mm – intermediate means need higher dose, or resistant so cant get enough at liscened dose
Resistance is not black and white – spectrum
