Transcript Controlling Bacteria

Controlling Bacteria
Antimicrobial Agents (Bactericide)
Chemical substances that either kill
bacteria or inhibit bacterial growth without
harming the host
3 Types of Antimicrobial Agents
1. Antiseptics - chemicals used to inhibit
the growth of or kill bacteria on living
tissues
2. Disinfectants - chemicals used to inhibit
the growth of or kill bacteria on nonliving
things
3. Antibiotics - compounds that block the
growth and reproduction of bacteria
How Antimicrobial Agents work
Inhibition of cell wall synthesis
Damage cell membranes
Inhibit the synthesis of DNA or RNA
Inhibit protein synthesis
Inhibit enzyme activity
Bacterial Inhibition Lab
Level 5 Formal Lab
Lab Objective
To test the effectiveness of 3 bactericides
You pick the bactericides you want to test
You need to bring them to class next Monday
(except for the antibiotics), small samples
State the problem
Write the question that you are trying to answer
Hypothesis
If … then … because
Be sure that your “because” is reasonable
Include name of bacteria being used
Which bacteriacide will be most effective?
Provided Materials
 Bacillus subtilis or
E-coli (decide)
 Petri dish with agar
 Inoculating loop
 Bunsen Burner
 Tweezers
 Filter paper discs
 3 bactericides of your
choice (name them)
 Sharpie marker
 Parafilm wax
 Ruler
 Alcohol
 Distilled water
 Incubator
 Goggles
Procedure
Pay attention to the next couple of slides
and to the demonstration
Think about the materials provided
Write a logical procedure
Your procedure will be due and checked prior to
starting the experiment
SterileTechniques
1. Dip loop in alcohol
2. Heat loop and wire to red-hot.
Flame the handle slightly
2. Allow the loop to cool for 5
seconds.
3. Remove a loop full of the
organism from the plate by
gently scraping the loop against
the bacterial lawn.
4. Streak the Plate
a.
b.
c.
d.
e.
f.
g.
Start at edge of the plate (Area A) with a loop
full of organism. Spread the organism in one
single continuous movement towards the
opposite side of the plate. Use light pressure
and avoid gouging the agar.
Replace lid
Flame loop and let cool
Obtain another loop full of organism
Start at the opposite edge of plate (Area B)
with loop full of organism and spread in
continuous movement toward the opposite
side of the plate.
Replace lid
Flame loop, let cool, and return
Get This Checked Off To Start Lab
by next Monday:
Investigative question
Hypothesis
Materials list (Your group supplies antiseptics and
disinfectants)
Procedure (logical)- 3 procedures
sterile technique
Streaking
setting up your petri plate
Variables
Data- diagram of plate before (how is it set up), data
table for zone of inhibition, picture of plate after
(drawn or with camera)
How to Measure the effectiveness
 Measure the Zone of Inhibition
area around a paper disk or colony of bacteria or mold
where no other organisms are growing
measurements are made to quantify the relative
effectiveness of a compound
Collecting Data
Fill in data table:
- Find diameter of zone of inhibition
- Measure in mm using the ruler
- Draw a picture/ or take a picture of your plate,
shade in where there is bacteria
- Write conclusion (with data #’s as supporting
evidence)
- Write error analysis
- Lab books will be stamped at the beginning of
class Monday/Tuesday.
How to Measure the effectiveness
 Measure the Zone of Inhibition
area around a paper disk or colony of bacteria or mold
where no other organisms are growing
measurements are made to quantify the relative
effectiveness of a compound