Here is Callum’s way of thinking about antibiotic and the spectrum of action.

<aside> 💡 Building a basic diagram of pathogenic bacteria

</aside>

First let’s consider organisms by their most simple classification:

Gram positive/negative

Cocci/bacilli

Aerobic vs anaerobic is quite complex, but we want to think about anaerobes in some situations, and they can be from any of our four groups so we’ll put them in the middle (just like they are in the middle of the body, the gut!)

Slide1.PNG

Ok so what sort of organisms are in each quadrant? Let’s keep it simple and go with the major organisms (Loyal Listeners know there are many more)

Slide2.PNG

There are some KEY ORGANISMS we need to think about whether we need specific cover for. MRSA and Pseudomonas aeruginosa, so we’ll add those on

Slide3.PNG

Oh and don’t forget there are lots of bacteria that do not stain with Gram staining. The list of these is extensive but I’ve chosen some examples

Slide4.PNG

Oh, oh! One more step of complexity. We have dichotomised bacilli and cocci but in reality there is a lot of overlap and organisms can often be “coccobacillary” so it’s worth including that here. A good example is Haemophilus spp.

Slide5.PNG

So putting this together we have:

Gram positive

cocci

Staphylococci

Streptococci

Enterococci

MRSA

bacilli

Listeria

Gram negative

cocci

Neisseria

coccobacilli

Haemophilus

bacilli

Enterobacterales

Pseudomonas

Atypicals

Mycoplasma

Chlamydophilia

Legionella

<aside> 💡 Worked example of a clinical syndrome

</aside>

Ok the next level on our lasagne of thinking about antibiotics is considering the clinical syndrome our patient is presenting with.

Let’s start with CAP as it is relatively straightforward

I’ve put the important pathogens in larger font and bold, here they are roughly in order from highest to lowest priority for consideration:

Streptococcus pneumoniae

Haemophilus influenza

Mycoplasma/Chlamydophilia/Legionella

Klebsiella pneumoniae

Beta haemolytic Streptococci (e.g. Streptococcus pyogenes)

Slide6.PNG

So now we have our clinical syndrome and the organisms we think are important to cover.