Bacterial Diseases (AQA GCSE Biology): Revision Note

Bacteria: Basics

• Bacterial pathogens are cells that can infect plants and animals, causing disease

• Not all bacteria are harmful (so not all bacteria are pathogens) – both the skin and large intestine, in particular, are home to hundreds of different bacterial species that play a vital role in maintaining our health

  • Bacteria on the skin act as competitors to harmful pathogens

  • Bacteria in the large intestine digest substances we can’t in food (such as cellulose) and provide essential nutrients (such as Vitamin K)

• Bacterial pathogens produce toxins that cause damage to cells and tissues directly

• In certain optimum conditions, some bacteria can reproduce rapidly (with the fastest being once every 20 minutes for some species of E. coli)

  • Optimum conditions usually involve warmth, moisture and a supply of nutrients

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Salmonella

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

• It is found in the gut of many different animals

Symptoms

• The symptoms of a salmonella infection start between 8–72 hours of eating infected food

• The bacteria secrete toxins that cause the body to react with: fever, abdominal cramps, vomiting and diarrhoea.

• These symptoms are the body trying to remove the infection from the gut

• Generally the infection doesn’t last for more than a few days. It is more serious in young children and the elderly due to the dehydration it causes

How is it spread?

• Contaminated food that has not been cooked properly is the main cause of salmonella food poisoning

• It can be found in eggs and egg products that are not cooked, such as mayonnaise

Treatment & prevention

• Chickens in the UK are vaccinated against salmonella.

• Proper hygiene in the kitchen:

  • Preventing raw meat from contaminating cooked meat

  • Cooking all food thoroughly, not washing raw meat (it spreads the bacteria around the kitchen)

• Washing surfaces and hands before and after handling raw meat, especially chicken

Gonorrhoea

• Gonorrhoea is a sexually transmitted disease (STD) – these diseases are also called sexually transmitted infections (STI)

• In 2018 it had the largest increase (26%) of infections in the UK

  • a total of 56 259 cases

  • it was the cause of 13% of diagnosed STDs

Symptoms

• In the early stages, symptoms include a thick, yellow or green discharge from the vagina or penis and pain when urinating

• Some infectious men and women can be asymptomatic

• Left untreated it can cause infertility, ectopic pregnancies and pelvic pain

• Babies born to women with the disease can get eye infections and be born blind

How is it spread?

• Gonorrhoea is spread by unprotected sexual contact

Treatment & prevention

• Barrier methods of contraception such as the condom can prevent the spread of gonorrhoea

• Can be treated with antibiotics, but now many strains are becoming resistant to the most used antibiotic penicillin

• Tracing of all sexual partners is essential so that all individuals can be tested and treated