A short, 22 second video of bacteria multiplying was doing the rounds of the internet last week. But why did it have so many scientists excited? First, a bit of an explanation about how bacteria grow and multiply…
What do bacteria look like?
Bacteria are single cell organisms and can be round, rod-shaped or wavy. They are covered by a thin membrane and then a thicker, protective cell wall. This cell wall is made up of proteins and sugars linked together. Inside, bacteria contain DNA and little protein “factories” called ribosomes. There are also several “optional extras” that bacteria may have:
- Flagella: tails that help bacteria move around
- Fimbriae: little fingers that help bacteria stick to surfaces
- Capsules: thick shells that protect bacteria from antibiotics and the body’s immune system.
Bacterial multiplication: from 1 to a million in 3…hours?
Below is a diagram showing how bacteria multiply. First, they grow in size and DNA content. The DNA then moves to opposite ends of the cell, and proteins assemble along the middle. Special proteins pinch the cell into two, while cell wall proteins fill in the gaps.
In the right environments, bacteria can multiply quickly. For example, Clostridia (the bacteria that causes Blackleg) can double in number every 10 minutes while E. coli (a cause of calf scours and mastitis) doubles every 20 minutes. This means bacteria could go from 1 to a million in a bit over 3 hours! Other bacteria are slower growing: the bacteria that causes tuberculosis, Mycobacterium tuberculosis, takes 12 hours to double in number.
How do antibiotics work?
There are many types of antibiotics and they work in different ways to stop bacteria from growing. They can inhibit DNA production or interfere with ribosome function (so that proteins can’t be produced). Other antibiotics interrupt the production of the cell wall during multiplication: they disable the enzyme that links cell wall proteins together. Not enough cell wall is produced to cover both of the new cells and so they die.
Bacteria: fighting back!
Bacteria don’t just sit around waiting to be killed. They evolve and exchange ways to resist antibiotics. For example, some bacteria produce enzymes that destroy certain antibiotics. The mastitis pathogen Staph. aureus is a well-known bacteria that does this: it can produce the enzyme beta-lactamase that inactivates penicillin.
In the presence of the antibiotics that interfere with cell wall production, bacteria can also mutate into a different form that doesn’t have a cell wall at all. They are called “L-forms” and are covered only by the cell membrane. And while fragile and a funny shape, some survive without rupturing. When antibiotic treatment finishes, these L-form bacteria return back to the cell-walled state, ready to multiply again. The tricksters!
Newcastle University in the UK recently caught this phenomenon on video for the first time, hence the internet excitement. L-form E. coli from human patients being treated for urinary tract infections were able to reform a cell wall just 5 hours after the antibiotics were removed.
Halloween is coming up: if the kids want to dress up as something scary for trick or treating, perhaps antibiotic resistant L-form bacteria could be the go?