3.1.3 Bacterial Diseases · 3. Infection and Response | Aqa GCSE Combined Science Trilogy 8464: Biology

Section 1 of 9Bacteria as pathogens

Binary Fission in Bacteria — Full 2D Simulation

Bacteria are single-celled organisms without a nucleus.

They multiply rapidly by binary fission when conditions are warm and there is a food supply,

so a few bacteria that enter the body can become millions within hours.

Toxins

Bacteria make you ill in two main ways: they damage your cells directly, and they produce toxins that poison the cells.

Unlike viruses, bacteria can be killed by antibiotics, although antibiotic resistance is a growing problem.

Section 2 of 9Salmonella food poisoning

Salmonella bacteria cause food poisoning.

1

The bacteria are often found in raw poultry, eggs and meat.

2

People are infected when they eat food that is undercooked or has been contaminated, for example when chopping boards or hands transfer bacteria from raw chicken to food that will not be cooked.

3

The bacteria multiply in the gut, and the toxins they produce cause the symptoms: fever, abdominal cramps, vomiting and diarrhoea,

which usually begin within 12 to 72 hours of eating.

4

Most healthy people recover without treatment, but the loss of fluid can be dangerous for the very young or very old.

Control measures include:

1

Vaccinating poultry against Salmonella in many countries, such as the UK.

2

Cooking meat and eggs thoroughly, because heat kills the bacteria.

3

Keeping raw and cooked foods separate and washing hands and surfaces.

4

Storing food in a refrigerator, because low temperatures slow the multiplication of bacteria.

Section 3 of 9Gonorrhoea

Gonorrhoea is a sexually transmitted infection (STI) caused by bacteria. It spreads by sexual contact. The symptoms are pain when urinating and a thick yellow or green discharge from the vagina or the penis. If untreated, it can cause infertility in women because the infection can damage the reproductive organs, and it can be passed to a baby during birth.

In the past, gonorrhoea was treated with the antibiotic penicillin, but many strains of the bacterium have become resistant to it, so other antibiotics are now used.

Gonorrhoea

Spread is reduced by using a barrier method of contraception such as a condom, and by testing and treating the infected person and their partners.

People with gonorrhoea should avoid sexual contact until they have been treated.

Section 4 of 9Comparing the two diseases

	Salmonella food poisoning	Gonorrhoea
Spread	Contaminated food, hands and surfaces	Sexual contact
Symptoms	Fever, cramps, vomiting, diarrhoea	Pain on urination, thick yellow/green discharge
Treatment	Usually rehydration; antibiotics for severe cases	Antibiotics (resistance to penicillin is common)
Prevention	Hygiene, thorough cooking, vaccination of poultry	Condoms, treating partners

Section 5 of 9Antibiotic resistance and public health

Both diseases show why public health matters.

1

Salmonella outbreaks can be traced to a source such as a batch of eggs, and removing the source stops the spread.

2

The rise of resistant gonorrhoea is an example of natural selection: where antibiotics are used, bacteria that happen to resist them survive and reproduce,

so the resistant strain becomes more common.

3

Doctors therefore try to prescribe antibiotics only when they are needed, and patients should complete a course of treatment.

4

This links to the antibiotics lesson later in this topic.

Section 6 of 9Bacteria and the immune response

When Salmonella or gonorrhoea bacteria enter the body, white blood cells recognise their antigens and respond (see lesson 3.1.6).

Bacteria and the immune response

The fever that occurs in food poisoning is part of this response: a higher body temperature slows bacterial growth.

Fluid loss in vomiting and diarrhoea is harmful because it upsets the balance of water and ions in the body,

so drinking plenty of fluids, often with salts, is the main treatment.

Gonorrhoea often causes few symptoms in some people, particularly women, who may pass it on without knowing,

so screening and contact tracing are important in controlling it.

You should be able to compare bacterial diseases with viral ones: bacteria are cells that can be killed with antibiotics, whereas viruses are not cells and cannot.

For a long-answer question, show that you understand the link between cause and control: toxins explain the symptoms of food poisoning, rapid multiplication explains why food must be kept cold, and natural selection explains why resistant gonorrhoea has appeared. Name the pathogen type and the disease each time.

Section 7 of 9Exam-style questions

How antibiotic resistance can spread in the gut

Antibiotic resistance: resistant bacteria survive and multiply

How Antibiotic Resistance Can Spread in the Gut — Animated

How Penicillin Kills a Bacterial Cell — Animated

How penicillin works on bacterial cell wall

How diseases are transmitted (spider diagram)

Explain why food poisoning caused by Salmonella is more likely if chicken is not cooked properly. [3]3 marks
Describe how the spread of gonorrhoea can be reduced. [2]2 marks
A person takes antibiotics for gonorrhoea but the infection continues. Suggest an explanation. [2]2 marks

Section 8 of 9Key terms

Term	Meaning
Bacterium	A single-celled organism with no nucleus.
Toxin	A poison produced by bacteria.
Salmonella	Bacteria that cause food poisoning.
Gonorrhoea	A sexually transmitted bacterial infection.
Sexually transmitted infection	An infection spread by sexual contact.
Penicillin	An antibiotic that kills bacteria.
Antibiotic resistance	The ability of bacteria to survive treatment with an antibiotic.

Section 9 of 9Exam technique

1

Saying that food poisoning is caused by the food itself going 'off' rather than by bacteria and their toxins.

2

Writing that Salmonella is spread by droplets in the air.

3

Saying that antibiotics cure all STIsthe cause must be bacterial, and resistant strains exist.

4

Stating that vaccinating people prevents Salmonella: it is the poultry that are vaccinated.