Bacterial diseases (AQA GCSE Biology): Revision Notes
Bacterial diseases
What are bacteria?
Bacteria are tiny living things called prokaryotic organisms. This means they don't have a proper nucleus like plant and animal cells do. Many bacteria can act as pathogens, which means they cause diseases.
Unlike plant and animal cells (eukaryotic cells), bacterial cells have their genetic material freely floating in the cytoplasm rather than enclosed in a membrane-bound nucleus.
A bacterial cell is quite simple. It contains:
- Cytoplasm - the jelly-like substance inside the cell
- A loop of DNA - the genetic material that controls the cell
- Plasmids - small rings of extra DNA
- A cell membrane - the thin layer around the cell contents
- A cell wall - a tough outer layer that protects the bacteria
Key features of bacteria
Bacteria have several important characteristics that help them cause disease:
- They are usually much smaller than plant and animal cells, but bigger than viruses
- They can reproduce very quickly once inside your body
- Some bacteria make poisonous substances called toxins that damage your tissues and make you feel unwell
- They can infect both plants and animals
- They spread through direct contact, contaminated water, or through the air
Two well-known bacterial diseases are cholera and tuberculosis (TB).
The rapid reproduction rate of bacteria is one of the main reasons why bacterial infections can become serious so quickly. Some bacteria can double their population every 20 minutes under ideal conditions.
How bacteria spread disease
Bacteria can get into your body and cause infections in several ways. Once inside, they multiply rapidly and some produce harmful toxins that damage your cells and make you sick.
Examples of human bacterial diseases
Salmonella food poisoning
Example: Salmonella Food Poisoning
How it spreads:
- Eating food that contains the Salmonella bacteria
- Eating food that was prepared in dirty conditions
Symptoms:
- Fever - your body temperature goes up
- Stomach cramps - painful feelings in your belly
- Vomiting - being sick
- Diarrhoea - loose, watery stools
Gonorrhoea
Example: Gonorrhoea
How it spreads:
- Through sexual contact between infected people
Symptoms:
- Thick yellow or green discharge from private parts
- Pain when urinating (passing water)
Treatment and prevention
Antibiotics
Bacterial diseases can be treated using antibiotics. These are medicines that kill bacteria or stop them from growing. However, there's a growing problem with antibiotic resistance. This means some bacteria have changed so that certain antibiotics no longer work against them.
Antibiotic Resistance - A Growing Concern
Antibiotic resistance occurs when bacteria evolve to survive antibiotic treatments. This makes infections harder to treat and can lead to more serious health complications. For example, gonorrhoea used to be easily treated with penicillin, but now many strains are resistant to multiple antibiotics.
Prevention
One important way to prevent bacterial diseases is through good hygiene. The story of Ignaz Semmelweis (1818-1865) shows how important hand washing is:
The Pioneer of Hand Hygiene
Semmelweis noticed that many women died from infections after childbirth. He realised that doctors might be spreading germs between patients on their hands. When doctors started washing their hands before examining patients, death rates dropped dramatically. At the time, nobody understood about germs, so he couldn't explain why hand washing worked so well.
Other prevention methods include:
- Using condoms during sexual activity to prevent STDs like gonorrhoea
- Proper food hygiene to prevent Salmonella poisoning
- Cooking food thoroughly and storing it properly
Remember!
Key Points to Remember:
- Bacteria are prokaryotic organisms that can cause diseases by producing harmful toxins
- Bacterial cells have a simple structure with cytoplasm, DNA, plasmids, cell membrane and cell wall
- Salmonella spreads through contaminated food and causes fever, cramps, vomiting and diarrhoea
- Gonorrhoea spreads through sexual contact and causes discharge and pain when urinating
- Antibiotics can treat bacterial diseases but antibiotic resistance is a growing problem
- Good hygiene, especially hand washing, helps prevent the spread of bacterial diseases