Question

How many bacteria would it take to cover the entire digestive tract?

Answer 1

It would take 3 × 10¹³ bacteria to cover the entire digestive tract.

Explanation:

I will make some assumptions:

1. The bacteria are all the same size as E. coli.
2. A typical bacterium is 2 µm long and 0.5 µm wide.
3. The mucosal surface of the digestive tract interior averages ∼32 m² (of which about 2 m² is the large intestine).

The last two estimates come from the National Center for Biotechnology Information.

Step 1. Calculate the area of a bacterium.

`A = l×w = "2 µm" × "0.5 µm" = "1 µm"^2`

Convert this area to square metres.

`A = "1 µm"^2 × ("1 m"/(1 × 10^6color(white)(l)"µm"))^2 = 1 × 10^"-12"color(white)(l)"m"^2`

Step 2. Calculate the number of bacteria required.

The area of the digestive tract is 32 m² (about half the area of a badminton court).

`"Bacteria required" = "32 m"^2 × "1 bacterium"/(1 × 10^"-12"color(white)(l)"m"^2) = 3× 10^13color(white)(l)"bacteria"`

That's 30 trillion bacteria!