Superbug

Antioxidants like vitamins A and C, which prevent the breakdown (oxidation) of nitric oxide in the body. But NO is very short-lived, hence its usefulness as a signalling molecule.

Are you planning to count colonies at the different depths? Because I'm not sure you'll be able to differentiate single colonies, although you'll be able to say whether the inoculum grew or not. I'd just use test tubes and have a single tube per experiment. Do you think antibiotics will work differently at different depths?

It's not an experiment, but one of the coolest examples of evolution is the spread of antibiotic resistance throughout a range of disease causing bacteria (in my some what geeky opinion any way!). It's also a good way of getting the kids of today to realise that the use of antibiotics as if they were candy to be taken for every little cough and sniffle can only mean bad things for mankind. Something scary to do would be to take swabs of various places in the school/home and plate onto agar plates with different antibiotics to see how common antibiotic resistance is.