How is natural selection shown in the development of antibioticresistant strains of bacteria?

Answer 1

Exposure of a population to a toxin that kills a high percentage of the population selectively eliminates those individuals most susceptible to the toxin. This leaves the most resistant individuals to reproduce individuals that are also resistant. After many generations of this selection the whole population is resistant.

Answer 2

When a population of bacteria is bombarded with antibiotics, the 'weak' ones will die. The ones with some resistance built in will survive, and divide to form a new population of copies of themselves, or a resistant population. This in itself is survival of the fittest in a very pure form. The 'selection' of stronger individuals that survive to breed is natural selection.

Answer 3

If we didn't use an antibiotic (methacillin), we would not have selected for those bacteria that had a resistance gene. Now we have to contend with that MRSA (methacillin resistant Staphylococcus aureus). By using the methacillin, we are producing a selecting environment.

Answer 4

Say a population of bacteria is treated with a antibiotic. Most of the bacteria die, but a few survive. The have been natural selected because their traits that lead to their survival are passed on to the next generation of bacteria which now have these traits of survivability and reproductive success. Natural selection leading to evolution.

Answer 5

The antibiotics humans use selects for the development of resistance by killing non-resistant bacteria.

Normally there are many kinds of bacteria on your body, called your natural flora. If a bacterium is producing extra enzymes to counter antibiotics then is tends to grow more slowly because it's using energy to produce these substances. This usually means that this bacterium will be selected against since other, less resistant bacteria can grow faster and out-compete it. However, if the bacteria are in an environment that is exposed to antibiotics, then the resistant strain is selected for. The non-resistant bacteria will all be killed off, leaving the antibiotic-resistant bacteria to thrive and grow exponentially. They are able to monopolize the area because they can survive and there is no competition to keep their numbers down. This shows selective pressures against the non-resistant bacteria and for the resistance.

In some cases (such as MRSA) one kind of bacteria has multiple genes against many different kinds of antibiotics. The overuse of different antibiotics has favored their survival. This makes them very difficult to destroy and very serious if an infection occurs.