Social Factors That Affect Good Health
Senior 1 · Biology
Social Factors That Affect Good Health
Lesson 4 of 5
25 min
Byiringiro had a bacterial chest infection. The health centre gave him an antibiotic: one capsule three times a day for seven days. By day 3 his fever had gone, so he stopped taking the capsules and kept the rest "in case". Two weeks later the cough was back, worse than before. This time the same antibiotic did not help, and he had to be sent to the district hospital for a different one.
The antibiotic was the same, and so was the patient. What changed was the bacteria. To see why, you need the idea of natural selection.
Definition
Antibiotic: a medicine that kills bacteria or stops them from growing, by attacking structures that bacteria have and human cells do not, such as the bacterial cell wall. Example: penicillin. Antibiotics have no effect on viruses, so they cannot cure a cold, influenza or HIV infection.
Course (of treatment): the full number of doses a health worker prescribes, taken at set times for a set number of days.
Definition
Antibiotic resistance: the ability of bacteria to survive and multiply in the presence of an antibiotic that used to kill them. It is part of the wider problem of antimicrobial resistance (AMR), in which bacteria, viruses, fungi or parasites stop responding to the medicines used against them.
Natural selection: the process in which individuals with a feature that helps them survive in their surroundings live longer and reproduce more, so the feature becomes more common in later generations.
Among the billions of bacteria in an infection, a few are slightly different from the rest by chance: they survive the antibiotic a little better. Figure 1 follows two patients with the same infection.
Figure 1: The antibiotic does not create resistance; it selects it. Stopping early leaves the toughest bacteria alive to multiply and spread.
Taking the full course as prescribed (row B) keeps the antibiotic in the body long enough to finish the job, with the help of the body's own defences.
Worked example 1: explaining Byiringiro's story
Use the four steps of Figure 1 to explain why the antibiotic failed the second time.
Key idea: the antibiotic did not make the bacteria resistant; it selected the resistant ones by removing their competitors.
Worked example 2: how much of the course was missed?
The prescription was 1 capsule 3 times a day for 7 days. Byiringiro took all his capsules for 3 days.
Answer: he missed more than half of the course, and the 12 capsules he kept are dangerous: taken later for a different illness, they would be the wrong dose, and possibly the wrong medicine.
Worked example 3: reading the disc test
A hospital laboratory tests the bacteria from a patient in the same way as the photo. Around the disc of antibiotic P the clear ring is 25 mm wide; around antibiotic Q there is no ring at all. Which antibiotic should the doctor choose?
Answer: antibiotic P. This is why laboratories test bacteria before choosing treatment for serious infections: it avoids wasting time on a medicine that cannot work.
Warning
Use antibiotics safely
The WHO estimates that bacterial antimicrobial resistance was associated with more than 4.7 million deaths worldwide in 2021, and that about 1 in 6 laboratory-confirmed bacterial infections were resistant to antibiotics in 2023. It names the misuse and overuse of antibiotics as the main driver, together with poor access to clean water, sanitation and hygiene, which lets resistant bacteria spread. Antibiotics given to farm animals when they are not needed also select resistant bacteria, so livestock keepers should use them only on a veterinarian's advice.
This links back to Lesson 2: every case of diarrhoea prevented by a latrine and a bar of soap is one less course of antibiotics, and one less chance for resistance to be selected.
What causes antibiotic resistance? (TED-Ed, 5 min). Watch for the moment the few resistant bacteria are left behind, which is Figure 1's step 2, and for how bacteria can also pass resistance genes to each other.
Your friend has a sore throat and a runny nose. Her sister offers her some antibiotic capsules left over from last month. Using what you have learned, write the advice you would give your friend, with two scientific reasons.
Tip
Memory hook: "Stop early, and the strong survive." Whenever a course is cut short, picture Figure 1's row A: the few tough bacteria are the ones left to multiply.
Practice: antibiotics and resistance
Key points
Sources and credits
Figure 1, the worked examples, the decision task and the practice questions are written by Ganzaa.
