• Single-celled organisms found in all types of environments
• Can only be seen through a microscope - measured in micrometer (one millionth of a meter)
• Prokaryotes - they do not contain a nucleus
• Grouped in families - having the same bacterial ancestors. E.g. Enterobacteriaceae
• A family member is a genus - each genus having developed its own peculiar characteristics. E.g. Escherichia
• A genus has different species E.g Escherichia Coli (E. Coli)
• Different shapes, sizes and many other characteristics
Bacteria can be harmless, beneficial or harmful (pathogenic) . . .
Do not affect humans
Beneficial Bacteria produce enzymes that:
• Aid food digestion and production of some vitamins - break down complex food molecules into simpler materials (especially in ruminants); Responsible for production of vitamin K and some b vitamins
• Are Involved in production of many foods eaten by humans - milk souring bacteria are used to produce yogurt, cottage cheese, and buttermilk; other bacteria used to produce vinegar and sauerkraut
• Are the principal agents of putrefaction - the anaerobic decomposition of organic materials, especially protein (i.e. contains nitrogen); produces foul odors
• Are the principal agents of decay - the gradual decomposition of organic matter exposed to air by bacteria and fungi.
Pathogenic bacteria cause disease by different mechanisms:
• Directly attack tissues (in other life-forms) - E.g.Bacterial Leaf Spot caused by Pseudomonas cichorii
