a method for testing antimicrobial susceptibility . A plastic strip is used that has a defined concentration of drug on one side and an interpretive scale of minimal inhibitory concentrations on the other side; it is put on the surface of an agar medium inoculated with the microorganism to be tested. This method is most useful for fastidious bacteria such as Streptococcus pneumoniae , Haemophilus influenzae , and certain anaerobic bacteria.