Question 8 of 8 Click Submit to complete this assessment. Question 8 10 points S

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Question 8 of 8 Click Submit to complete this assessment. Question 8 10 points Save Answer Knowing a mid stream urine culture was streaked with a 1ul loop and grew 80 clear colonies on the MacConkey agar at 24 hours, what would be reported? 800 cfu/ml of a lactose fermenting gram negative rod. Identification will follow. O 8,000 cfu/ml of a non-lactose fermenting gram-negative rod. No additional work up 80,000 cfu/ml of a lactose fermenting gram negative rod. Id and susceptibility will follow. 80,000 cfu/ml of a non- lactose fermenting gram-negative rod. ld and susceptibility will follow.

Explanation / Answer

Ans. MacConkey agar is a differential media that distinguishes lactose fermenters (pink-colored colonies) from non-lactose fermenters (clear colonies). Simultaneously, it also acts as selective media by inhibiting the growth of Gram-positive bacteria. So, only Gram-negative bacteria grow in the medium.

# So, the 80 colonies observed after Gram-negative, and non-lactose fermenters.

# Now,

            CFU count of inoculum = Number of colonies / Volume of inoculum

                                                = 80 colonies / 1.0 uL

                                                = 80 colonies / 0.001 mL

                                                = 80000 colonies/ mL

# So, correct option is – D. 80000 CFU/mL of a non-lactose fermenting gram-negative rods.

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