Bacteria; How do we Kill Them?

I like focusing on the friendly, useful bacteria, but there are some pretty mean nasty ones out there that cause horrible diseases, wipe out crops, contaminate my experiments, and generally ruin everyone's day. That's where exciting things like antibiotics, sterilising procedures and autoclaves come in; they are our weapons, killing these unwanted bacteria. But how do they work? How do we actually kill bacteria?
Bacteria share many things with humans, which is handy for me because it's easier to relate things to people than to tiny creatures we can't really tangibly experience unless we jump into a compost heap. So before we get into killing bacteria, how does killing humans work?

I've never killed a human, but we all know the basics; shot, stabbed, poisoned etc. But you can experience those things without being killed, so what is the actual killing part? Physical killing, like gunshots, car accidents, stabbings etc, works by stopping important functions of the body, often by disrupting vital organs. I dropped a bowling ball on my hand once, which didn't kill me, but if I'd dropped it on my head it might have done, because that's where my brain lives, and I need that in order to be alive. Bacteria don't have brains, or hearts, or lungs, but things disrupting the vital parts of their system will kill them. We don't use knives for this, but things like antibiotics; for example, trimethoprim works because it stops DNA synthesis, which is pretty essential for life. Great! So method one of killing bacteria; mess with their important bodily functions.

Poisoning falls into that category too; in fact, it fits better with the bacterial thing because it works at the same cellular scale. Antibiotics are like poison, chemicals that kill cells. Like cyanide, which cuts off the respiratory pathways, depriving cells of energy, antibiotics interfere with biological processes in the cells.

The whole 'poking unwanted holes in people' factors of stabbing is similar to some other antibiotics,too! Many work by putting a hole in the wall of the cell, letting all the good stuff inside that the bacteria needs leak out. Penicillin works a bit like that too, by stopping the cell wall from growing when the cell is dividing.

It's not just antibiotics though; we kill bacteria every day, with heat when we cook our food, for example. Bacteria have lots of proteins in them, doing various things to keep them alive, and too much heat can change proteins so they don't work any more. Just look at what happens when you fry an egg; that's the proteins in the albumen getting changed by the heat. Acid does this too; milk thickens into yoghurt when enough acid is produced by the bacteria eating it, changing the shape of proeins in the milk so they gloop together. We can relate this to humans too, I wouldn't want to jump in some acid or sit in the oven! Although I hate heat anyway so don't want to sit near the oven at all...

Of course bacteria have ways of avoiding these causes of death, just like we do. Antibiotic resistance is growing, and is really bad news. Often this works by the bacteria deactivating the antibiotic before it can kill them; like at the start of Casino Royale when James Bond takes all the bullets out of the guy's gun before he shows up. Or the bacteria evolve to be less affected by things, with tougher proteins that can withstand more heat, like when we put on oven gloves.

But my point is, that bacteria die for the same reasons as us; things stop working in their body. So we can kill them by making things stop working!

99% of them at least though, right? But I'll go into that one another day.