Answer:
In a macrotube (macrobroth) dilution susceptibility test,
1.0 ml of Mueller Hinton (MH) broth is pipetted into tubes 2 through 10, tube 11, and tube 13.
Two milliliters of MH broth is pipetted into tube 12;
1.0 ml of 200 micrograms/ml of ampicillin is added to tubes 1, 2, and 13.
A twofold serial dilution is performed in 1.0 ml amounts in tubes 2 through 10.
The standardized inoculum is diluted 1:200 and 1.0 ml is added to tubes 1 though 11.
The tubes are incubated for 20 hours at 350 C.
After this time, the tubes are examined for visual growth.
Tubes 6 through 7 are visibly turbid, while tubes 1 through 5 show no signs of growth. Tubes 1 through 5 are plated on blood agar, incubated overnight at 350C, and read for growth. Plates 1 through 4 show no growth while several colonies are observed on plate 5.
The MIC is:
The tubes 1 through 5.
Explanation:
The MIC is the tube which gets the lowest anti-biotic concentration showing no visible growth, and as tubes 6 through 7 are visible turbid.
