Hey so I was just playing Plague Inc when it got a question to pop into my head as I the game we can tell a virus from a bacteria or fungus because we are the one’s in control but can someone please how we can do that IRL or if we even can?
In: Biology
Yes we can, up to the point of general sequencing them entirely, but it’s a very broad question so I’ll pick an example to narrow it down.
Let’s say that you come in with fever and a cough. The first thing I do is take your symptoms and a medical history – how long have you had the cough? Is it getting worse or better? Do you have any other symptoms like headaches, diarrhoea, pain anywhere? Have you travelled anywhere recently? Is anyone else sick? What do you do for work? Do you have any other conditions? Etc. etc
I then look at signs – these are things I can test. I might listen to your lungs with a stethoscope, take your temperature, tap on your chest to listen to see if the sound changes, take your pulse and blood pressure and blood oxygen etc.
You have a fever, a crackly chest, and a productive cough.
OK, so now I think that you have pneumonia. That’s an inflammation of the lungs, normally caused by infection. Infectious pneumonia is normally bacterial or viral – it can also be caused by fungi and parasites, but unless you have risk factors for these (like you’ve got AIDS or you’re a chicken farmer), we’ll focus on the first two.
I now might use imaging to help, so I send you off to radiology and you get a chest X-ray. I can see that one of the lobes of your lungs is all consolidated because it’s whiter than the rest, which are full of air. That’s normally associated with bacterial pneumonia, acquired in the community as you haven’t been in hospital recently, so that’ll be my running diagnosis.
If it isn’t that bad, I’ll use my medical knowledge and guidelines to pick a broad-spectrum antibiotic that targets the most common causes of pneumonia and send you off. However, you finish the course and it’s no better and you come back. Evidently my antibiotics didn’t work, so I need to find out what bacteria might be infecting you. I ask for a sputum sample (get you to hack up some phlegm into a pot) and send it off to the lab for testing. I also take blood samples, to get lots of different measurements including measures of immune function, infection, inflammation and also the type of white blood cells you have a lot of. Viral infections are targets by different types of white blood cells than bacterial infections, so this is useful to double-check.
In the lab, they take your sputum sample and then grow cultures from it on agar plates to multiply up the bacteria. Some of it is stained and looked at under a microscope – different types of bacteria take on different stains, and the shape of the bacteria can also help with diagnosis. Some bacteria are grown on different growth media – they’re fed different foods and given different chemical challenges to see if they grow, as this helps with diagnosis too.
If we think it’s antibiotic resistant, we might try growing it with different concentrations of different antibiotics to find one that works.
After all of this, we’ve found out that it’s *Haemophilia influenzae* resistant to our normal antibiotics, so we follow guidelines and give you levofloxacin. You survive, hooray!
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