Bacterial diseases

Infection and response · Communicable diseases · note 3 of 9

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Bacterial diseasesSpec 4.3.1.3

In short

Salmonella food poisoning and gonorrhoea are bacterial diseases. Salmonella is spread in food, and its symptoms are caused by the bacteria and the toxins they secrete; UK poultry are vaccinated against it. Gonorrhoea is a sexually transmitted disease that was easily treated with penicillin until resistant strains appeared. It is controlled with antibiotics and condoms.

Salmonella food poisoning

Salmonella food poisoning is spread by bacteria ingested in food, or on food prepared in unhygienic conditions.

The fever, abdominal cramps, vomiting and diarrhoea are caused by the bacteria and the toxins they secrete.

In the UK, poultry are vaccinated against Salmonella to control the spread.

Gonorrhoea

Gonorrhoea is a sexually transmitted disease (STD) caused by a bacterium. The symptoms are a thick yellow or green discharge from the vagina or penis, and pain on urinating.

It was easily treated with the antibiotic penicillin until many resistant strains appeared. It is spread by sexual contact.

The spread can be controlled by treatment with antibiotics or by using a barrier method of contraception such as a condom.

Two bacterial diseases compared
	Salmonella food poisoning	Gonorrhoea
Spread by	Eating contaminated food, or food prepared in unhygienic conditions	Sexual contact
Symptoms	Fever, abdominal cramps, vomiting, diarrhoea	Thick yellow or green discharge; pain on urinating
Control	Vaccinating poultry in the UK	Antibiotics; barrier contraception such as a condom

Exam tip:

Use the full name 'barrier method of contraception' or 'condom'. 'Protection' is too vague for a mark.

Written and checked against the AQA GCSE Combined Science (8464) specification · Updated October 2026

Frequently asked questions

How do pathogens spread?

Pathogens spread by direct contact, by water or by air. HIV and gonorrhoea spread by sexual contact, and HIV also by the exchange of body fluids such as blood. Measles spreads in droplets from sneezes and coughs, and rose black spot by water or wind. Salmonella spreads in food, and malaria is carried by mosquitos.

How do white blood cells fight infection?

White blood cells fight infection in three ways. Some engulf and digest pathogens, which is called phagocytosis. Others produce antibodies, which target a particular pathogen and help to destroy it, and antitoxins, which neutralise the toxins released by pathogens. This is the immune system, which acts when a pathogen gets past the non-specific defences.

How do vaccines work?

Vaccines work by introducing small quantities of dead or inactive pathogen into the body, which stimulates white blood cells to produce antibodies. If the same pathogen enters the body later, the white blood cells respond quickly to make the correct antibodies, so the pathogen is destroyed before it causes illness. A vaccine does not contain antibodies itself.

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