Match controls to targets and read antibiotic-susceptibility results.
Loading saved practice…
Method and worked examples
Antibiotics act on susceptible bacteria by targeting bacterial structures or processes. They do not directly treat viral replication. Antiseptics reduce microorganisms on living tissue; disinfectants are used on suitable non-living surfaces. Sanitation, vector control and reduced exposure act at different parts of a transmission pathway. Their effectiveness depends on the actual route and agent.
Bacterial variants may already carry resistance, or acquire it through mutation or gene transfer. Antibiotic exposure can leave resistant variants with a survival advantage, increasing their proportion. The bacteria evolve; the person does not become antibiotic-resistant. In a supplied susceptibility table, a larger inhibition zone can indicate greater susceptibility under the same stated test conditions, but zone size alone does not specify a safe clinical treatment.
Example 1
A population contains 99 susceptible bacteria and 1 resistant bacterium. A treatment kills the susceptible bacteria only. What fraction of survivors is resistant?
The one survivor is resistant, so 11=100% of survivors. Its resistance was present before treatment in this scenario.
Example 2
A controlled table gives inhibition-zone diameters A=8mm and B=18mm. Which inhibits this strain more in the stated comparison?
B has the larger zone and shows greater growth inhibition under the stated matching conditions.
Watch out:Resistance is a property of bacteria; selection can increase resistant bacterial variants during exposure.
Antibiotics, resistance and control practice | Year 11 Biology | Ascent Arcade