Thread by @ProfDFrancis

Anything I say to give hard-pressed doctors a well-deserved laugh, has a risk of making some of them angry.

But this will amuse not only to every doctor, but everyone who has a science degree, and indeed a many other people who have merely been to school

off-guardian.org/2020/06/09/sci…

At first I thought Twitter was being a wet blanket and opposing fun and frolics.

But then I noticed the yellow text, and Twitter is right - there are some people uneducated enough to fall for this nonsense.

So here is a short thread to rescue people who have been misled by the Koch Postulators.

#MedEd #FOAMed

In your opinion, infections are caused by what?

Well in that case you don't need Koch's postulates. It is easy to forget that in 150 years, science has advanced so rapidly that even the dimmest bulb in the room finds certain things obvious.

But remember this is after many decades of explosive growth in science/engineering research.

This is the world in which Robert Koch lived.

(He is the one wearing black)

He was trying to work out what caused the deadly disease, Cholera.

Easy for us to say, "Oh it's just vibrio cholerae, the amusingly curved gram negative rod".

But that's because we've been to med school and seen the Gram stains and the electron micrograph.

But at that time, microscopy of bacteria was just getting going.

Robert Koch and Friedrich Loeffler were trying to help fellow scientists decide which of the many wriggly things they could now see, in and on the body, were doing the harm.

Incidentally this picture of Koch kept getting me in trouble at medical school. A girl next to me in a lecture had once whispered "You'd think his beard would keep dipping in the agar, wouldn't you?"

Unfortunately that made me laugh inappropriately every time I saw that photo.

So anyway, Koch said, "You can't blame any random wriggly thing for any ailment you like. There are a lot of them there bacteria, and a lot of diseases. You would go completely bonkers."

He came up with a simple checklist to stop you going crazy.

1. The wiggly thing must be there in people who got the disease, and not in those who don't got it.

("Yeh yeh that's really obvious Robertty boy", the crowd would have shouted back, "Get on with the good stuff.")

OK OK.

2. Get some of the wiggly things and grow them in a dish.

("What kind of dish? Can I use something from the kitchen?")

No. Wait. Let me get my assistant.

HEY JULIUS

Make yourself useful. Can you make a glass thing of this shape, so the wiggly things are spread out, and we can microscope through it without needing a separate slide preparation?

Stop whining. You can call it after yourself.

The "Julius Dish". People will love it.

THAT is how long ago this was. The poor old assistant had to invent the dish to put the bacteria on!

Due to his extensive "face time" with the dish, he wisely skipped the goatee element of the facial hair, preferring to go more sideways-y.

OK that's not it, says Koch.

3. The point of growing it in a dish, is so that you can suck up a blob of it and inject it into an animal, and make them die.

("Oooh nasty!")

Yes but otherwise it might be just something that grows in people who already have the disease.

He threw in a bonus postulate for keen people.

4. When the newly infected animal dies, and you chop it up, it should have the same wiggly thing that you started with. So you've seen it all along the causal sequence.

("Ah, now we get it! Hard work though.")

So there are the Koch's postulates, to stop us getting overexcited about the thousands of types of bacteria we can find in and on the human body.

1. See the thing in diseased patients and not in undiseased.
2. Can grow the bacterium in a dish.
3. ... and then inject into a healthy animal and cause the disease ...
4. ... and then see the bacterium in the diseased animal.

Seem fair?

Seems fair to me.

Worked very nicely for cholera.

Unfortunately, on the second thing he tried it for, at the time called "consumption", it didn't work so well.

Yes, people with tuberculosis did have Mycobaterium tuberculosis in them, and people without it, didn't.

(The pink things in the slide below)

So checklist number 1 - TICK!

But then when you try to grow them, they don't play ball.

Bugger.

They must have evolved millions of years ago, to annoy the hell out of poor old Koch.

1. They grow VERY slowly.
E Coli doubles in cell count every 20 minutes
M Tuberculosis does it every 20 HOURS.

2. They DON'T SHOW UP on Gram stains.

Devious!

Fortunately some people worked out a fancy stain which shows up M TB.

Taking their cue from Petri, they eschewed the name "Franz-Friedrich stain" and went instead for Ziehl-Neelsen.

3. It takes *months* to grow enough to see by the naked eye, and that is even with super specialised medium for them to grow on.

Anyway poor old Koch beavered away to prove the point that this really was the culprit.

It was an enormous struggle, in the case of TB.

He managed to do it in the end, and was awarded the Nobel prize.

(I'm sure he was careful to wash the bottom of his beard)

I'm sure this is now coming back to you from med school.

Because it would have been on about the second lecture in Infectious Diseases.

Viruses.

Viruses are

I don't know whether Viruses are alive or not, either.

I consider it a sterile debate (hahaha).

For viruses being alive:

They reproduce by the million or billion rather easily inside a human body. They inject their nucleic acid into our cells, and then force our cells' own machinery to make new virus particles, and eventually explode, releasing the virus particles.

Yup:

Against being alive:

On their own, with no living cells to scrounge ribosomes and stuff from, they can't reproduce.

A bit like millenials without Tinder.

So if you try to apply Koch's postulates to viruses, you can go ahead and bite a rabid dog, if you like.

When you catch rabies and die, you can have a cheery epitaph.

"Here lies Mr Clever Clogs.
Died of rabies virus.
But it doesn't meet Koch's postulates.
So it doesn't count, ya boo sucks!"

Same goes for:

Ebola and Marburg viruses
HIV
Smallpox
Hantavirus
Dengue fever
Cholera

and of course Covid-19

Please pass on this thread to any defiant Koch Postulators denying the existence of Covid-19.

Here is the start of it - thank you!

https://twitter.com/ProfDFrancis/status/1306848594364960768?s=20