PREDICTING THE GROWTH OF MICROORGANISMS

Objectives Students will Use sterile techniques to collect a sample Observe the growth of microorganisms on a nutrient agar plate Create nutrient jelly ideal for growing microbes for observation. Understand the environment for culturing microbial growth.

SUMMARY This lab is designed to give students a “hands-on” experience to help answer the question: How can you determine where in your environment you might find microorganisms?

KEY CONCEPTS Microbes are very small and have been around a long time Microbes are everywhere; they are extremely abundant and diverse

Growth is in a general manner a process where an individual organism is becoming larger. Bacteria, however, are so small that it is almost impossible to measure the growth of an individual. Therefore, the growth of bacteria is described through the size of their colonies. In relevant conditions, bacteria are growing so well that the number of bacteria increases twice in an hour or even with a shorter time.

Bacteria are very small, one celled, microscopic organisms that are found in air, water, soil, and the bodies of other living organisms. If provided with the right conditions they will multiply into a visible colony of bacteria cells. The nutrient jelly provides a nutritious environment where the bacteria and fungi can grow into a visible group of cells (colony).

PRECAUTIONS Most bacteria and fungi collected in the environment will not be harmful. However, once they multiply into millions of colonies in a petri dish they become more of a hazard. Be sure to protect open cuts with rubber gloves and never ingest or breathe in growing bacteria. Keep growing petri dishes taped closed. When the experiment is finished, a teacher or demonstrator should safely destroy the fuzzy bacteria colonies.

BACTERIAL COLONY MORPHOLOGY

Bacteria grow on solid media as colonies. A colony is defined as a visible mass of microorganisms all originating from a single mother cell, therefore a colony constitutes a clone of bacteria all genetically alike.

Edges (also called margin)

BACTERIAL SHAPES

PETRI DISH Is a shallow cylindrical glass or plastic lidded dish that biologists use to culture cells – such as bacteria culturecellsbacteria

AGAR Is a jelly-like substance, obtained from algae

Where can we find bacteria?

How can you find bacteria? You can’t see it, so how do you find it? Under the right conditions, bacteria grows very fast, exponentially Some bacteria populations can double every 10 minutes Bacteria grow in colonies – a colony is a visible mass of bacterial growth on solid medium that developed from 1 or a few cells A colony can contain millions of cells We can find bacteria by growing it in the right conditions until it is visible to the human eye

How to Sample Bacteria Get a sterile swab – don’t touch the cotton end Swab the area to be tested Open your Petri dish carefully and swab the cotton in the specified area on the agar Close the Petri dish quickly Get a new swab for each sample When done, close the Petri dish and use scotch tape to seal the sides Put the Petri dish upside down in a dark, warm place