Bacteria can sometimes adapt to the antibiotics used to kill them. This adaptation, which can involve structural changes or the production of enzymes that render the antibiotic useless, can make the particular bacterial species resistant to the particular antibiotic. Furthermore, a given bacterial species will usually display a spectrum of susceptibilities to antibiotics, with some antibiotics being very effective and others totally ineffective. For another bacterial species, the pattern of antibiotic sensitivity and resistance will be different. Thus, for diagnosis of an infection and for clinical decisions regarding the best treatment, tests of an organism's response to antibiotics are essential.

A standard method of testing for antibiotic resistance involves growth of the target bacteria in the presence of various concentrations of the antibiotic of interest. Typically, this test is performed in a specially designed plastic dish that can be filled with agar...