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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:

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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.

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