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1. Antibiotic Evaluation

The following set of data was taken from tests of antibiotics ontwo organisms isolated from the lungs of a patient with CysticFibrosis. These evaluations were carried out using the diskdiffusion method, and the diameter of the zone of inhibition (ZOI)is provided for each organism and antibiotic.

Pseudomonas aeruginosa is Gram-negative.

Corynebacterium xerosis is Gram-positive.

Resistant (R): ZOI ≤ 11 millimeters (mm)
Intermediate (I): ZOI > 11 mm and ≤ 17 mm
Sensitive (S): ZOI > 17 mm

Instructions: Evaluate the susceptibility ofeach organism to the antibiotics listed. Then, fill in the“Evaluation” columns with R, I, or S based on your analysis.

Antibiotic	Pseudomonas aeruginosa	Corynebacterium xerosis
	ZOI, mm	Evaluation	ZOI, mm	Evaluation
Penicillin	3		1
Erythromycin	12		33
Rifampin	11		2
Ciprofloxacin	19		27

Based on the results from these two organisms and the dataprovided, determine which antibiotics are broad-spectrum and whichantibiotics are narrow-spectrum.

Antibiotic	Spectrum
Penicillin
Erythromycin
Rifampin
Ciprofloxacin

2. Media preparation

2A. Of all the infectious agents we have discussed, at least oneof them can remain pathogenic after going through acorrectly-functioning autoclave. Which is it?

2B. To test our autoclaves at Southwestern we perform a monthly“Endospore viability” run. Explain why this is a good way todetermine if the autoclave is working properly.

3. Estimation of Bacterial Population Size

3A. Estimate the population of the original culture based on theinformation below:

               Number of colonies on plate: 74
               Volume plated: 0.1 mL
               Dilution of culture plated: 1/1,000,000 (1 x 10^-6)

Estimated population density (Be sure to include the correctunits!):

3B. If I took 0.5 mL of the original culture and diluted it into15 mL of water, how much would the original culture be diluted?

3C. Suppose that I took 1 mL of water from Sweetwater Reservoirand plated it onto TSA. After 1 day of growth, I counted 30colonies on the plate. Sweetwater Reservoir is estimated to haveapproximately

               34,000,000,000,000 milliliters of water (3.4 x 10¹³mL)

How many bacteria do you estimate are living in SweetwaterReservoir?