The size, shape and structure of bacteria

The size, shape and structure of bacteria


Baceira can only be observed under a microscope with a magnification of around 1000 times. Bacteria vary in size from around .001mm to .003mm. Alothough an individual bacterium cannot be seen, large numbers can be seen as small white or yellow spots on growth media in laboratories. These spots are known as colonies.

Large number of spoilage organisms may also cause visible effects on food, for example, discolouration, slime and odour.

Bacteria vary considerably in shape:

  • Cocci are spherical



  • Rods are sausage shaped



  • Spirochaetes are spiral



  • Vibrios are comma shaped




Cell wall – A rigid structure that gives the bacterium its shape.

Cell membrane – Controls passage of waste and nutrients into and out of the cell.

Cytoplasm – The ‘body’ of the bacterium.

Nuclear material – The ‘brain’ of the bacterium (Gives genetic characteristics).

Flagella – Attachment that allow bacteria to move in liquids.

Although some bacteria can use flagella to swim around in liquids, most bacteria rely on other objects to move them about, for example, moving from the one food to another using a table top, a piece of equipment such asĀ  knife or the hands of the food handler. Things which transfer bacteria from one place to another are known as vehicles.

As food poisoning bacteria are commonly found on raw food and people, it is impracticable to operate a food business without food poisoning bacteria being present at one time or another. It is therefore essential to deny them to multiply to a level where they present a risk to customers. ( Large numbers of bacteria usually need to be present in food of cause food poisoning.)