Bacteria are single-celled prokaryotes. They can reproduce very rapidly — doubling every 20 minutes under ideal conditions.
Bacteria cause disease in two main ways:
PRODUCING TOXINS — many bacteria secrete chemicals (toxins) that damage cells and tissues. It is often the toxins, not the bacteria themselves, that cause the symptoms of disease.
DIRECT CELL DAMAGE — some bacteria invade and destroy body cells directly.
Unlike viruses, bacteria CAN be treated with ANTIBIOTICS — drugs that specifically target bacterial structures (e.g. cell walls) that human cells don't have.
Salmonella Food Poisoning
CAUSE: Salmonella bacteria (various species).
TRANSMISSION: Eating food contaminated with Salmonella — most commonly undercooked poultry, raw or undercooked eggs, unpasteurised milk. Also spread through poor kitchen hygiene (cross-contamination from raw to cooked food) and unwashed hands.
SYMPTOMS: Begin 12–72 hours after eating contaminated food:
Fever.
Stomach cramps and abdominal pain.
Vomiting.
Diarrhoea (which can be severe and bloody).
Symptoms usually last 4–7 days.
MECHANISM: Salmonella bacteria survive cooking if the food isn't heated properly. They reach the small intestine, colonise the gut lining and produce toxins — causing the symptoms.
PREVENTION: Thorough cooking (bacteria are killed by heat), good hygiene (wash hands, clean surfaces), refrigeration (slows bacterial growth), pasteurisation of dairy products, vaccination of poultry flocks.
TREATMENT: Most cases resolve without antibiotics — rest and plenty of fluids. Severe cases may need antibiotics and hospital treatment.
Gonorrhoea
CAUSE: Neisseria gonorrhoeae bacteria.
TRANSMISSION: Sexual contact — a sexually transmitted infection (STI). Passed during vaginal, anal or oral sex without barrier contraception.
SYMPTOMS:
IN FEMALES: Often NO symptoms (asymptomatic) — this makes it particularly dangerous as it can spread unknowingly. When symptoms occur: thick yellow/green vaginal discharge, pain when urinating.
IN MALES: Thick yellow/green discharge from the penis, burning pain when urinating.
COMPLICATIONS: If untreated:
Pelvic inflammatory disease (PID) in females → can cause infertility.
Increased risk of HIV infection.
Can be passed from mother to baby during birth → eye infection in newborn.
PREVENTION: Using condoms (barrier contraception), reducing number of sexual partners, regular STI testing.
TREATMENT: Antibiotics — however, ANTIBIOTIC-RESISTANT strains have emerged, making gonorrhoea increasingly difficult to treat. This is a serious and growing public health problem.
ANTIBIOTIC RESISTANCE in gonorrhoea happens through natural selection:
Random mutations in bacteria can produce resistance.
Antibiotics kill non-resistant bacteria but resistant ones survive.
Resistant bacteria reproduce, passing on resistance genes.
Over time, the population becomes resistant.
⚠️ Common Mistake
Gonorrhoea IS treatable with antibiotics — but antibiotic-resistant strains are emerging. Do not say 'gonorrhoea cannot be treated'. Say instead: 'it can be treated, but resistance is a growing problem'. Also: Salmonella causes disease primarily through TOXINS — not just by the bacteria damaging cells directly.
📌 Key Note
Salmonella: bacteria, contaminated food, symptoms = fever/vomiting/diarrhoea, prevented by cooking thoroughly. Gonorrhoea: bacteria, STI, discharge and pain, treated by antibiotics (resistance growing).
🎯 Matching Activity — Match the Bacterial Disease to its Features
Match each feature to Salmonella or Gonorrhoea. — drag the symbols on the right to match the component names on the left.
Salmonella
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Gonorrhoea
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Salmonella
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Gonorrhoea
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Salmonella
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Sexually transmitted — thick discharge and pain when urinating
Bacteria produce toxins in the gut — causing vomiting and diarrhoea
Antibiotic-resistant strains have emerged — major public health concern
Spread through undercooked food — prevented by thorough cooking and hygiene
Often resolves without antibiotics — rest and fluids usually sufficient
🎯 Test Yourself
Question 1 of 2
1. How is Salmonella food poisoning prevented?
2. Why is gonorrhoea becoming harder to treat?
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