Question

Count the number of CFU from each of the plates (record TNTC if there are too many to count). Record your counts below and calculate the total number of bacteria per mL and the number of ampicillin-resistant bacteria per mL in the chicken fluid. Show all your calculations in a neat logical manner in the workspace on page 4.

Plate Count Plates Without Ampicillin
Dilution	CFU/Plate Plate # 1    Plate # 2		Average/Plate	CFU/mL of Fluid
10-4	52	80	66	66 x 104 / 1 ml = 6.6 x 105 cells/ml
10-5	12	12	12	12 x 105 / 1ml = 12 x 105 cells/m
10-6	0	0	0	No cells

            Total Number of Culturable Bacteria = 9.3 x 10⁵ cells/ml

           

Plate Count Plates With Ampicillin (10 µg/mL)
Dilution	CFU/Plate Plate # 1    Plate # 2		Average/Plate	CFU/mL of Fluid
10-3	59	255	157	1.57 x 105cells/ml
10-4	111	95	103	10.3 x 105cells/ml
10-5	12	9	10.5	(too few to count, they will not be considered for CFU calculation)

Number of Culturable Ampicillin-Resistant Bacteria = 1.57 x 10⁵ cells/ml + 10.3 x 10⁵ cells/ml / 2 = 5.9 x 10⁵ cells/ml

1. Were there several or only a few types of bacterial colonies on the antibiotic plates compared to the non-antibiotic containing plates? Comment on why your results do or do not make sense.   Describe the dominant colony/colonies on the non-antibiotic plates and on the antibiotic-containing plates

2. As mentioned in the introductory material, “The antibiotic that you will test today, ‘Ampicillin’, has been in use for a long time and was introduced commercially in 1961.” Do you think that your results would differ much if you had tested the fluid from the packaged chicken for resistance to a third generation cephalosporin (e.g., ceftriaxone) that was first issued for use in the 1980s instead of ampicillin? Explain

Answer 1

From the given data it is clear that bacteria ares sensitive to antibiotic.

ampicillin come under penicillin category. If any bacteria seems to be resistant to ampicillin means they are resistant beta-lactamase. these type of bacteria can be killed by using third generation cephalosporins like ceftraxone because they are designed to face beta-lactamase resistant bacteria.

Although the given samples are ampicillin sensitive, we can get more better results (less number of colonies) with ceftriaxone because of their more effectiveness.