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BACTERIA 
PLATES. Ring Around the Rosy Rhyme. Dates back to the Great Plague of London in 1665 (Bubonic Plague). Ring around the rosy, Pockets full of posies Ashes, ashes, We all fall down. Symptoms of the plague included a rosy red rash in the 
shape of a ring on the skin

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slide2

Ring Around the Rosy Rhyme

Dates back to the Great Plague of London in 1665 (Bubonic Plague)

Ring around the rosy,

Pockets full of posies

Ashes, ashes,

We all fall down.

Symptoms of the plague included a rosy red rash in the 
shape of a ring on the skin

Pockets and pouches were filled with sweet smelling 
hers which were carried due to the belief that the 
disease was transmitted by bad smells

Refers to the cremation of the dead

Refers to all the people dying from the plague.

slide3

In the two laboratory lessons that follow, you will start to understand 
that bacteria are everywhere and that various surfaces have different 
levels of organisms. It is very important to keep in mind that bacteria 
can spread from hands to food, from food to food, and from surfaces to 
food. This cross-contamination can be controlled by the simple measure 
of thoroughly washing hands and surfaces.

If you are going to test hands and under fingernails for bacteria, wash 
your hands after you have swabbed these areas.

If your going to test your mouth, do not put Q-tip in mouth!!! Use inoculating loop!

slide4

ASEPTIC CONDITIONS

Aseptic technique is a fundamental skill needed for any level of 
microbiological work. There are THREE basic components:

1) Sterilization: Lab equipment must be heated (>1000C) to kill resistant 
micro-organisms and their spores. This will prevent contamination of 
your cultures.

2) Working close to a flame: Never leave an open flame unattended, 
and always tie back your hair when working with a flame. The flame 
from a Bunsen burner is used to sterilize inoculation loops to maintain 
pure cultures.

3) Disinfection: Clean you bench top before and after use, to kill any 
cells. Wash your hands thoroughly after the experiment.

slide5

Safety Rules

- Leave all coats, books and bags that are not directly involved with the

lab at the back or side of the room to avoid contamination

- Students with long hair should tie this back to avoid contaminating the

work area

- Always wash your hands with soap and water before leaving the lab

- Do not put pencils, pens, etc. in your mouth; avoid touching your eyes

after handling the samples

- Do not remove the cultures from the lab

- Treat all cultures like they are potential pathogens.

- At the end of the procedure, wipe down your working surface

slide6

Inoculating the Petri Plates

Before you begin part 2, obtain petri dish and using permanent marker divide the dish in four quarters, label C, 1, 2, 3

1

2

C

3

Procedure:

1.

Choose your source of microorganism....

If you choose a nonliving source use the Q-tip to swab your source (that has been 
soaked in boiling distilled) and smear it gently on the agar's surface 
(All over C, 1, 2,& 3) C will be your control.

If you choose a living source (mouth) provide an oral rinse sample using the 
bottled water provided. After sterilising the inoculation loop, dip loop into oral 
sample and transfer an onto the 4 quadrants of the agar plates.

(Exercise Caution not to puncture the agar)

Dip a paper disc in the disinfectant or antiseptic depending on what you 
choose using forceps that have been sterilized in a Bunsen burner flame.

2.

3.

Open the petri dish slighly to place the disc inside on the agar. (Place 
disc in area marked 1). Do this twice more with different disinfectants or 
antiseptics.

Reminder label these areas

4.

Use masking tape to secure the lids of the Petri plate.

Invert the agar plate and place the plate in an incubator 
(Lab 213), set at 300C.

Observations:

1) Draw the growth on the plate after 24 hours.

slide7

2

1

3

C

Observations:

1a) Measure the growth ring around a disk, as indicated by the following diagram.

  Four measurements should be taken from the centre of the disk. 

1

2

4

3

b)  #1 (mm) #2 (mm) #3 (mm) #4 (mm) Average(mm)
Antiseptic 

Disinfectant 

slide8

DESCRIBING BACTERIAL CULTURES

Shape of Colony

Circular

Irregular

Filamentous

Raised

Flat

Wavy

Entire

slide9

Analysis

1. What chemical agents did you use to slow/stop the growth of microorganisms?

2. Which chemical agent was the most successful?

3. What type of microorganisms grew in the petri dish? (Describe shape, colour, type of edges)

4. Write definitions for antiseptic, and disinfectant.

5. When discussing bacteria the word antibiotics often comes up why is this so?

6. Besides chemicals, what other techniques can be used to stop the growth of microorganisms. (Provide 2)

7. List 3 ways in which industry makes use of microorganisms.

8. List the 3 conditions that typically enhance bacterial growth.