Bacteria need food too, just like we do.
Some bacteria don’t require much. Give them your basic, bare minimum foods (carbs, proteins/amino acids, salts, etc) and they’ll grow happily. Most bacteria we use in the lab like growing at 37 degrees (our average body temp) under normal atmospheric conditions…
And then you get these suckers.
The bacteria I work on don’t like it when you just give them your basic food mixes. They are extremely fussy. First of all, they don’t like growing unless it’s very acidic (pH of 4.75, to be precise). They also can’t make a lot of amino acids themselves, and prefer to scavenge them from the environment… which means you have to make sure they’re all added. They also don’t like lots of oxygen, and prefer a precise growing condition of 37 degrees, 5% carbon dioxide and 2.5% oxygen.
There’s two kinds of culture media (ie. thing that we grow bacteria in/on) we can use. One is liquid, and the other is solid (see photo above). On solid media, my bacterial colonies (which are isolated dots of billions of bacteria growing on top of each other) only grow to the size of tiny dust specks. The kind you see on your phone screen. You know, the ones that are so small that you don’t even bother wiping it off.
The above photo is my trial attempt at trying to grow the colonies to a size that we can actually see without squinting. I have two sets of culture media. One is the standard one we use for this bacteria, and the other one is… essentially the same sort of media but more… complicated. I have to add all 20 essential amino acids individually, which can be painstaking (and hence, “complicated”). But, the bacteria do grow better in it, so I’m hoping that if I leave them in the incubator for long enough, they’ll grow big and strong and we can actually count the individual colonies.
Why is it important to count colonies?
In my case, I’m trying to figure out whether different strains of my bug with mutations in a specific gene (a gene that goes on to make a protein that is seemingly important for this bug) are more susceptible to certain antibiotics. If I get less mutant bacteria growing on the plates after antibiotic treatment, compared to ones I haven’t mutated, then maybe that mutation makes them weaker in a way that can be exploited by the antibiotics I’ve added.
Either way, long story short- pouring plates for fussy bacteria sucks.
Also, those plates need TWO layers! Pour one layer (which is more solid), wait 20-30 minutes to dry, then add the top layer (semi-liquid), dry another 20-30 minutes.
AND I have to grow them for 12 days!! Standard is 6-7 days. These bacteria are slooooooooow.
But we do love them anyway. I mean- why would I study them if I didn’t?
Categories: Ph D posts
A Ph. D graduate in Microbiology, residing in Victoria, Australia. Currently working in multiple locations but still in the STEM field. 👀 🦠 🧫 🧬