Topic 2.2
What are bacteria?
Here, you’ll discover the fascinating world of bacteria—tiny, single-celled organisms that can be both helpful and harmful to humans. While some bacteria support vital processes like digestion and food production, others can cause diseases. You’ll explore the different bacterial shapes, understand how scientists identify bacterial infections and learn how structure plays a role in their behaviour.
Bacteria
Bacteria are tiny, living cells ranging from 5 to 20 micrometres in size. A micrometre is a millionth of a metre.
Not all bacteria are harmful. Some have been used for centuries to help make cheese and yoghurt. However, certain types, known as pathogenic bacteria, can cause diseases such as cholera, salmonella, tuberculosis, and E. coli.
How Bacteria Make Us Sick Once inside the body, pathogenic bacteria can release chemicals called toxins. These toxins, along with the body’s immune response, often lead to symptoms of illness.
Bacteria Cell Structure
Bacteria Cells are simple with four main parts:
- Cell Wall: Helps maintain shape and prevents bursting
- Bacterial DNA: Controls the division of the cell and how the cell functions
- Plasmid DNA: Small pieces of extra DNA, circular in shape, that jump between bacteria
- Flagellum: Helps bacteria move, not essential
Types of Bacteria
Bacteria come in various shapes, which help scientists identify different types of infections:
1. Coccus (Spherical)
2. Bacillus (Rod)
3. Spirochete (Spiral)
These shapes assist in bacterial classification and are crucial in diagnosing infections.
Coccus
Round-shaped bacteria, often forming clusters or chains. Examples include Streptococcus and Staphylococcus.
Bacillus
Rod-shaped bacteria, sometimes forming pairs or chains. Common examples are E. coli and Salmonella.
Spirochete
Spiral or corkscrew-shaped bacteria, which are flexible and move in a twisting motion. Borrelia (causes Lyme disease) is an example.
Case Study Campylobacter jejuni infection
You’ve just had a bad case of food poisoning. You’ve been infected with Campylobacter jejuni which is a type of bacteria. Symptoms appear within 1-5 days. Campylobacter jejuni is the most common cause of food poisoning and is often found in raw chicken.
Bacterial cells can multiply every 20 minutes. So, if you start with 2 cells, in 20 minutes, you will have 4. After 40 minutes, you will have 8. After 60 minutes, 16 cells and so on.
If you ate the chicken at 7 pm and ingested 2 bacteria cells, when will you have over 250 cells?
The infective dose can be as few as 1 or 2 bacteria.
Discussion Prompts
- How do you think the shape of bacteria might affect their ability to spread or cause disease in humans? For example, would rod-shaped bacteria spread differently than spherical bacteria?
- In what ways could understanding bacterial shapes help scientists and healthcare professionals diagnose infections more quickly and accurately