<em>Clostridium tetani</em> b/w <em>Clostridium tetani</em>

Clostridium tetani

These bacteria are usually found in soil they enter the body through breaks in the skin. Clostridium tetani causes tetanus (lockjaw). This is a serious human disease that causes painful tightening of the muscles, usually all over the body. It can lead to "locking" of the jaw so the victim cannot open his mouth or swallow.

Observing bacteria in a Petri dish

Students should examine cultures in containers, which have been taped and closed. Colony morphology is a method that scientists use to describe the characteristics of an individual colony of bacteria growing on agar in a Petri dish. It can be used to help to identify them.

Different types of bacteria will produce different-looking colonies, some colonies may be coloured, some colonies are circular in shape, and others are irregular. A specific terminology is used to describe common colony types. These are:

  • Form - What is the basic shape of the colony? For example, circular, filamentous, etc.
  • Size – The diameter of the colony. Tiny colonies are referred to as punctiform.
  • Elevation - This describes the side view of a colony. Turn the Petri dish on end.
  • Margin/border – The edge of a colony. What is the magnified shape of the edge of the colony?
  • Surface - How does the surface of the colony appear? For example, smooth, glistening, rough, wrinkled or dull.
  • Opacity - For example, transparent (clear), opaque, translucent (like looking through frosted glass), etc.
  • Colour - (pigmentation) - For example, white, buff, red, purple, etc.

Each distinct colony represents an individual bacterial cell or group that has divided repeatedly. Being kept in one place, the resulting cells have accumulated to form a visible patch. Most bacterial colonies appear white or a creamy yellow in colour, and are fairly circular in shape.