This is a really fun and creative take on both the theme and on tower defense games in general.
I love the artstyle used here, its simple but very evocative.
One thing i did notice is that some of the germs are very unbalanced, especially the ones that spread themselves, specifically the worms were basically essential to winning every time, id suggest making every spreading germ relatively weak, so theres a bit of an element cycle going on with weak spreading germs < single powerful ones < gimmicky germs/thorns.