Antibiotics/soil Experiment

Question 1

What are antibiotics?

Answer 1

chemotherapeutic agents produced by microorganisms that kill or inhibit bacteria

Question 2

What are the four cell targets of antibiotics?

Answer 2

•Cell wall
•Cell membrane
•Protein synthesis
•DNA replication

Question 3

What was the purpose of plating the soil samples on a TSA-CHX (cycloheximide) plate?

Answer 3

To prevent fungal growth

Question 4

What piece of equipment did we use to inoculate the TSA-CHX plates after serial dilutions were performed?

Answer 4

A p100 micropipette and then a bacterial spreader

Question 5

What is PBS and why did we use this during the isolation process?

Answer 5

A non-toxic solution, which prevents cells rupturing or shrivelling up due to osmosis.

We wanted to give the bacteria from the soil an isotonic environment to maintain osmotic balance

Question 6

What was the purpose of performing serial dilutions prior to plating the bacteria?

Answer 6

To get isolated colonies

Question 7

Which piece of equipment did we use to inoculate the plates with bacteria?

Answer 7

A p100 micropipette

Question 8

What piece of equipment did we use to spread the bacteria evenly on the plates?

Answer 8

A bacterial spreader

Question 9

What is a CFU?

Answer 9

(Colony functioning unit) a cluster of cells that are the same species that form a colony

Question 10

How many bacteria are required to form an isolated colony?

Answer 10

1

Question 11

What is the statistical range for countable colonies?

Answer 11

30-300

Question 12

Know the formula for calculating CFU/g and be able to use the formula to quantify the number of bacteria of a sample (example: What is the CFU/g if 100 microliters of a 1ml sample of a 10 -4 dilution resulted in 95 colonies?

Answer 12

CFU/g= number of colonies X 1 / total dilution plated

Question 13

How were you able to differentiate the different bacteria that grew on your TSA-CHX plates?

Answer 13

Colony morphology ; unique colonies and characterize them according to size, pigmentation, form, elevation, margin, and surface

Question 14

What did you use to patch the bacteria on the master plates?

Answer 14

A sterile toothpick

Question 15

What type of media was used for antibiotic screening?

Answer 15

MH; Mueller Hinton plates

Question 16

How was this plate inoculated with the tester strains?

Answer 16

a process called picking and patching.
Each master plate will be divided into a 12-section grid to accommodate up to 12 unique isolated colonies

Question 17

How were the isolates inoculated on this plate after the plates have been inoculated with the tester strains?

Answer 17

With a sterile toothpick

Question 18

After incubation, did you tell which soil isolates were antibiotic producers?

Answer 18

by checking for clear zones around the growth (the positive control will be an example of clearing)

Question 19

What is the difference between narrow spectrum, broad spectrum, and intermediate spectrum antibiotics?

Answer 19

classified by the number of bacteria that they have an affect on.
Narrow spectrum- effective against one to a few groups
Broad spectrum- effective against many groups’ bacteria
Intermediate spectrum- effective against a moderate number of groups

Question 20

How did you classify your antibiotic producing soil isolates as narrow, broad, or intermediate spectrum?

Answer 20

narrow