Spectrum of activity; Range of efficiency; Range of activity

The spectrum of efficiency includes the entirety of microorganisms sensitive for an antibiotic drug. It can be supposed that germs with similar characteristics can be treated with the same antibiotic. One of the criteria to distinguish between different bacteria is the way they react on Gram's stain. Bacteria, which accept the dye, appear blue when they are looked at under the microscope. They are called gram positive. In gram negative germs the dye is washed out, after a second coloring with another dye they appear to be red under the microscope.