Question: Have you ever been sent a disease or bacterium that you couldn't find a test for?

Hannah Tanner answered on 20 Jun 2014:

Interesting question.

The laboratory can’t be sent a disease. Disease is the word we use to describe anything that goes wrong with someone that stops them being 100% healthy (except physical injuries).

Most of the time we find bacteria in samples from patients by putting part of the sample onto agar plates and seeing if anything grows. Most of the time we can easily recognise what kind of bacteria are growing but sometimes we grow something rare or unusual that we can’t easily put a name to. When this happens we do have extra tests that can identify them.

It’s harder when we think there is a bacterium in the sample but it’s one that isn’t growing on agar plates (not all bacteria do). In these cases we can look for the bacteria DNA and sometimes we find that and can say what bacteria were in the sample.

We can always design a test for something we know about. The problem is the unknown unknowns. The bacterium that no-one has discovered yet and no-one knows how to grow is always harder (but maybe not impossible) to find.