Structure and Function: Bacteria

Bacteria are microscopic single-celled organisms that are found in every environment. Some bacteria live in or on our bodies without causing disease. There are thousands of different types of bacterium, but relatively few of these cause disease in humans. Bacteria have a variety of shapes that are broadly classified as cocci (spheres), bacilli (rods), and spirochetes and spirilla (curved forms).


Bacteria may exchange genes in a process called conjugation. Plasmids, which may contain genes that give the bacteria resistance to antibiotics, are passed through tubes called sex pili.




Effects of toxins

Some bacteria cause disease by producing poisonous chemicals known as toxins. These chemicals may destroy specific body cells or enter cells and alter their chemical processes. Some toxins are released from bacteria when they die and may cause shock and fever.

The toxin is released into the body by the bacterium. The toxin attaches to a body cell and is absorbed into the fluid cytoplasm.

The toxin disrupts normal chemical reactions inside the cell, so that the cell is unable to function and dies.

Bacterial invasion of a cell

A few bacteria damage tissues in the human body not by secreting toxins but by directly invading the cells. Once inside body cells, the bacteria reproduce and eventually burst out, rupturing the cell membrane.

Different bacteria are specifically attracted to certain body cells. Bacteria enter the cell through the membrane and use the cell nutrients.

The bacteria multiply rapidly in the cell. They kill the cell by breaking its membrane then spread to other areas of the body.

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

The subjects, conditions and treatments covered in this encyclopaedia are for information only and may not be covered by your insurance product should you make a claim.

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