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 synthesisDamage cell membranesInhibit the synthesis of DNA or RNAInhibit protein synthesisInhibit enzyme activity

Bacterial Inhibition Lab

Level 5 Formal Lab

Lab Objective

To test the effectiveness of 3 bactericidesYou pick the bactericides you want to testYou need to bring them to class next Monday

(except for the antibiotics), small samples

State the problemWrite the question that you are trying to answer

HypothesisIf … then … because

Be sure that your “because” is reasonableInclude name of bacteria being usedWhich bacteriacide will be most effective?

Provided Materials

Bacillus subtilis or E-coli (decide)Petri dish with agarInoculating loopBunsen BurnerTweezersFilter paper discs

3 bactericides of your choice (name them)

Sharpie markerParafilm waxRulerAlcoholDistilled waterIncubatorGoggles

Procedure

Pay attention to the next couple of slides and to the demonstration

Think about the materials providedWrite a logical procedure

Your procedure will be due and checked prior to starting the experiment

SterileTechniques

1. Dip loop in alcohol2. Heat loop and wire to red-hot. Flame the handle slightly2. 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. 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.

b. Replace lidc. Flame loop and let coold. Obtain another loop full of organisme. 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.

f. Replace lidg. Flame loop, let cool, and return

Get This Checked Off To Start Lab by next Monday:

Investigative questionHypothesisMaterials list (Your group supplies antiseptics and

disinfectants)Procedure (logical)- 3 procedures

sterile techniqueStreakingsetting up your petri plate

VariablesData- 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 Inhibitionarea 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 Inhibitionarea 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