Chemotherapy Tests
Achemotherapy testis a scientific test that determines which antibiotic combats
a particular pathogen. These tests are used to determine which antibiotic to pre-
scribe to treat a specific disease. The antibiotic is called a chemotherapeutic agent.
There are two popular chemotherapy tests: diffusion methods and the broth
dilution method.DIFFUSION METHODS
Diffusion methods are tests that place a paper disk or plastic strip that is coated
with a chemotherapeutic agent in touch with a pathogen to determine if the
chemotherapeutic agent inhibits the pathogen. There are two commonly used
diffusion methods. These are the disk-diffusion method and the minimal
inhibitory concentration method.
The disk-diffusion method, also known as the Kirby-Bauertest, uses a filter
paper disk that is coated with the chemotherapeutic agent being tested. The
paper disk is placed in a Petri plate that contains an agar medium that has been
contaminated with the pathogen. The Petri plate is then incubated during which
the chemotherapeutic agent diffuses onto the agar. A zone of inhibition can be
seen in the agar medium. A zone of inhibition is the area where the pathogen
does not grow because the chemotherapeutic agent inhibits it. Scientists meas-
ure the diameter of the zone of inhibition and compare the diameter to a stan-
dard table for the chemotherapeutic agent. The table indicates whether the
pathogen is sensitive, intermediate, or resistant to the chemotherapeutic agent.
The minimal inhibitory concentration (MIC) test is an advanced diffusion
method that determines the lowest concentration of the chemotherapeutic agent
that inhibits the visible growth of bacteria. This test uses a plastic coated strip that
contains a gradient concentration of the chemotherapeutic agent. The strip is then
exposed to the pathogen, after which the strip is compared to a printed scale to
determine the minimal inhibitory concentration of the chemotherapeutic agent.BROTH DILUTION METHOD
The broth dilution method is used to determine the minimal inhibitory concen-
tration and the minimal bactericidal concentration (MBC) of the chemothera-(^246) CHAPTER 16 Antimicrobial Drugs