Lab IIIB: Introduction to Culturing and Characterizing Bacteria

Question 1

Is E. coli gram + or -?

Answer 1

gram -

Question 2

Is B. subtilis gram + or -?

Answer 2

gram +

Question 3

What does a positive star agar test indicate?

Answer 3

The bacteria have the gene to create the enzyme amylase to perform hydrolysis of starch

Question 4

Is penicillin effective against gram-positive or negative cells?

Answer 4

PENICILLIN against GRAM POSITIVE +++++

Question 5

Why is Penicillin effective against gram +?

Answer 5

b/c it inhibits the enzyme that crosslinks the peptidoglycan polymers

Question 6

So what does it mean if a bacterial species is sensitive to penicillin?

Answer 6

it would indicate that it’s gram-positive

Question 7

Does E. coli require the gene for amylase? and why? (knowing that the primary habitat of E. coli is the large intestine of many warm-blooded animals)

Answer 7

NO, the starch will have already been hydrolyzed by the organism by the time it reaches the large intestine, so E. coli does NOT require the gene for amylase

Question 8

What does Cefotaxime target?

Answer 8

Inhibition of CW synthesis

Question 9

What does Norfloxacin target?

Answer 9

inhibition of enzyme required for DNA replication

Question 10

What does Penicillin target?

Answer 10

inhibition of CW synthesis (inhibits the enzyme that crosslinks peptidoglycan polymers)

Question 11

What does Streptomycin target?

Answer 11

inhibition of bacterial ribosomes requires for protein synthesis

Question 12

In order of MOST sensitive to least sensitive to E. coli (+++, ++, ++, -)

Answer 12

Norfloxacin (+++), Streptomycin (++), Cefotaxime (++), Penicillin (-) [N, SC, P]

Question 13

In order of MOST sensitive to least sensitive to B. subtilis (+++, ++, ++, -)

Answer 13

Norfloxacin (+++), Streptomycin (++), Penicillin (++), Cefotaxime (++) [N, SPC]

Question 14

Based on the expected results, which antibiotic would be BEST to differentiate b/w E. coli and B. sub?

Answer 14

Penicillin

Question 15

How come Norfloxacin targets both gram + & - bacteria equally?

Answer 15

b/w its mechanism of action involves DNA replication, required for all bacterial cells to reproduce

Question 16

How to measure the zone of inhibition?

Answer 16

measure edge to edge across the zone of inhibition over the center of the disk (diameter)

Question 17

What does it indicate if there is a LARGE diameter?

Answer 17

it indicates high susceptibility to the antibiotic
(so small diameter = low susceptibility)

Question 18

What does it mean if there is no zone of inhibition? (so just the diameter of the disk)

Answer 18

it indicates that the bacterial species is NOT susceptible to that antibiotic (so it’s resistant)

Question 19

What is an endospore?

Answer 19

a resistant, dormant cell triggered by adverse conditions

Question 20

What genera of bacteria produce endospores?

Answer 20

Bacillus & Clostridium

Question 21

A positive result for the starch agar test indicates that the bacterial species has a gene for and produces which enzyme?

Answer 21

amylase

Question 22

Give all info on Gram-positive bacteria

Answer 22

• THICK peptidoglycan
• plasma membrane

purple

Question 23

Give all info on Gram-negative bacteria

Answer 23

• OUTER MEMBRANE
• think peptidoglycan
• plasma membrane
• pink/red