Question

2. The MIC, Kirby Bauer and E-TEST are all tests that are used to determine which antibiotics work against specific bacteria. a. Your patient comes in with a Staphylococcus aureus infection and you know that tetracycline kills S. aureus, but you want to prescribe the patient with the lowest concentration of tetracycline, which test would you conduct to find the lowest concentration that killed off S. aureus? b. Your patient comes in with a mystery bacterial infection. You want to prescribe an antibiotic, but you don't know which antibiotic will kill this mystery bacteria. Which test would you conduct to find the most effective antibiotic to this mystery bacteria? c. Which test will tell you if a bacteria is susceptible to an antibiotic AND the lowest concentration of that antibiotic in the same test?

Answer 1

2 a) The minimum concentration of an antimicrobial agent such as antibiotics that stops the proliferation of a microorganism is known as the minimum inhibitory concentration of MIC. It can be determined by Etest or Epsilometer test.

The patient has Staphylococcus aureus infection which could be treated by tetracycline. In this case, the antimicrobial agent is tetracycline.

The test which is required to test the lowest concentration of an antimicrobial agent that kills a particular microorganism (S. aureus in this case) is known as the Minimum bactericidal concentration test. This test is conducted following the MIC determination.

b)

The antibiotic required to kill the mystery bacteria could be determined using the Kirby Bauer test. This test is also known as a disk diffusion test. Various antibiotics can be tested against the culture of mystery bacteria. The clear zones in the test will indicate the antibacterial action of antibiotics against that mystery bacteria.

c)

The antibiotic susceptibility and the lowest concentration of the antibiotic of that antibiotic or MIC both can be found using Etest or Epsilometer test used in conjugation with the agar plate lawn method. It provides the antibiotic concentration needed to inhibit the concerned bacteria using an antibiotic strip. This will provide the MIC value for the antibiotic. The agar plate lawn method will provide the susceptibility of the antibiotic against the bacteria.