Good question! Well, it’s not like a fitness gym that you would recognise.
I have a particular bacteria, called Staph, and I have created a whole family of them, but unlike your own human family, each member of this family are almost identical, like identical twins. However, the one thing that IS different about each of them, is that they are resistant to a different antibiotic medicine.
Antibiotics are what we use to kill bacteria (or stop them growing), and each different antibiotic works in a slightly different way. There are different ways that a bacteria might avoid being killed by an antibiotic, in the same way that you have different ways to avoid getting wet in a rain storm (avoiding it, staying under cover, using an umbrella, wearing a rain jacket etc). My question is, does the ability to survive an antibiotic actually make the bacteria unfit when there is no antibiotic around?
Imagine you are having a running race in the rain against one of your friends, but you are dressed in a waterproof jacket and carrying an umbrella. The aim is to get to the other end without getting wet. You would have a better chance of winning the race against your friend by avoiding getting wet, wouldn’t you?
However, what happens when it’s no longer raining? If you did the same race, but this time you just had to be the first to get to the end, if you still had your waterproof jacket on, and your umbrella, these would get in the way, so you might lose. In this race you would be ‘unfit’ as there is no advantage to you carrying your waterproofs.
Now imagine that instead of rain we have antibiotics, and instead of umbrellas, we have some ability of the bacteria to resist the antibiotic, and imagine the friend that you were racing is just another bacteria, but that doesn’t have any ability to resist the antibiotic. My race is not a race for distance, but a race to see who can grow the fastest, and in my race there is no antibiotic (like the race without rain).
Who is going to win? Well, usually it’s the one that doesn’t have to carry loads of stuff. However, sometimes the one carrying loads of stuff does just as well as the one carrying nothing!
How does it do that? Well, that’s what I’m trying to find out.
I also want to find a particular LOSER, the one type of bacteria that was carrying a particular type of resistance (I guess it’d be like carrying a HUGE umbrella) that made it do really badly in the race, or in fact, makes it stop half way along, run out of breath and decide to stop racing. This would be a really unfit guy, and it means these guys can ONLY win a race if there is antibiotic around (like you only being able to win the race if its raining). What’s good about that is that we know if we don’t use the particular antibiotic it likes to race in, this guy is going to vanish, which is a good thing.