Growing Bacteria

Goal 11.04

What do bacteria need to grow?

• Moisture• Space • A comfortable temperature (warm)• An energy source and nutrients –

– sugars (glucose and others), or– sunlight (for some types)– chemicals (for the Archaebacteria)

• Incubator – similar to an oven, can be kept at a nice warm temperature, around 32 C.

• Nutrient Agar or Broth– contains energy source– other nutrients– moisture– certain antibiotics sometimes

How do we provide what they need to grow?

Equipment needed:

Incubator

Image from Shelly Scientific www.shellyscientific.com - GI6 SHEL LAB Digital Laboratory Incubator

Nutrient Agar or Broth

Images from Connecticut Valley Biological www.connecticutvalleybiological.com - Tryptic Soy Agar Plates, pkg of 10Nutrient Broth 150 mL

• Environmental sampling: Take a very small part of the

environment and streak it onto a plate or blend a sample and dilute it, and add the diluted sample to the plate.

• Mother culture: Growing bacteria of a certain type. Bacteria of certain types can be ordered from science supply companies.

How do we get the bacteria?

DilutionStart with the item in question:

Liquefy it: This is your sample:

Dilution

From your sample:

Fill a sterile tube with 50% sample and 50% sterile broth:

Repeat:

And keep repeating until you reach the dilution you want:

This is necessary because the original sample may contain billions of bacteria and each of these can become a colony. If you want to be able to tell what kind of bacteria are present, then you need to have only a few colonies.

Bacteria are everywhere and can fall into containers from the air and from you.

1. Sterilize surfaces with 70% alcohol.2. Wear gloves. Don’t touch your face or

surfaces.3. Keep everything closed until you need to

use it. 4. Tilt open containers, and keep lids off of

the counter. Hold them , without touching the inside.

5. Use sterile equipment, or run the loop, or glass spreader through a flame or dip in alcohol between uses.

Sterile Technique

Streaking a plate:1. Take the swab or loop containing

your sample. 2. Rub it gently back and forth on the

top 1/3 of the plate, not overlapping the streak.

3. Take a sterile loop and drag it from the place you rubbed into the adjacent 1/3 of the plate.

4. Re-sterilize the loop and go from the part of the plate you just rubbed across to the last clean spot.

Plating the bacteria

Spreading a plate:1. Add a small amount of liquid sample to

your plate, usually 2 - 3 drops, or 100-150 uL.

2. If using a glass spreader, make sure it is sterile, and cool. Place the spreader just in front of the area with the drops, and smear them in a circular path around the plate.

3. An alternate is to place sterile glass beads on the plate and roll them around until you feel like they have covered the area of the plate.

Plating the bacteria

After the sample has been added to the plate, we say the plate has been inoculated.

The plate should be labeled on the bottom with the date, initials of the person who plated the bacteria and sample name.

The next step is to keep the plate in a dark, warm place for 24 to 48 hours. This step is called incubation.

The next part of this lesson will discuss what we do with the bacteria once we have grown them.

Incubating the sample: