BACTERIA

Bacteria are the most abundant living organism on Earth. They are simple, cellular organisms which lack membrane bound organelles (eg. no nucleus, mitochondria, chloroplasts, etc). Most bacteria range in size from 0.5-4μm.

The great majority of bacteria live freely in the environment and do not cause disease. However there are many medically important species.

Traditionally, bacteria are divided into three categories based on their appearance :


Cocci (“balls”) eg. Streptococcus, Staphylococcus (“Golden Staph”), Neisseria (cause of gonorrhoea)





Bacilli (“rods”) eg. Bacillus, E. coli, Salmonella, Clostridium






Spirochaetes (“spirals”) eg. Treponema (cause of syphilis)


Some bacteria do not easily fit into these categories, however (eg. Diptheria causing bacteria are oval shaped). Most bacteria can only be told apart through certain biochemical tests.

Bacterial metabolism is often quite different to our cellular processes. Therefore, chemicals can be used which will kill bacteria but not affect us (eg. antibiotics)