Genetics Problem

Here is my take on it Princess...

Over the past five years, Farmer Smith, by treating his pigs with low doses of antibiotics, has been selecting for bacteria that are resistant to the antibiotics. The doses used killed sensitive bacteria, but not those bacteria that were moderately sensitive or slightly resistant. Over time, only resistant bacteria will be present in his pigs because any sensitive bacteria will have been eliminated by the low doses of antibiotics. The pigs that died this past year were infected by bacteria that had become so resistant they were not killed by even high doses of antibiotics. In the future, Farmer Smith can continue to use the vitamins, but he should use the antibiotics only when a sick pig requires them. In this manner, he will not be selecting for antibiotic-resistant bacteria, and the chances of the antibiotic therapy successfully treating his sick pigs will be greater. Lower doses may potentially decrease the chances of mutation, so rather than causing these genetic mutations really quickly (within five years), it would likely take longer.

Make sense?

Yh kinda but am confused to which part belongs to b and which belongs to c?

Is this part for b:

b. In this manner, he will not be selecting for antibiotic-resistant bacteria, and the chances of the antibiotic therapy successfully treating his sick pigs will be greater.

c.Lower doses may potentially decrease the chances of mutation, so rather than causing these genetic mutations really quickly (within five years), it would likely take longer.

c. Would this have happened without the low doses of antibiotics in the food? Explain

No, it would not have happened because recall, exposing bacteria to too many antibiotics encourages spontaneous and direct mutation. If he hadn't exposed them to low levels over a 5-year period; the bacteria probably wouldn't have mutated and been susceptible to the antibiotics.

b) Bacteria can pass their genetic information from oneself to another via 3 major methods. 1) conjugation (using sex pili), 2) when the bacteria lyses, the resistance gene is taken in by nearby bacteria, 3) horizontal gene transfer. Because of the antibiotics resistance is required to grow, bacteria would be more willing to accept the resistance gene and all other bacteria w/o the resistance would be killed off due to natural selection. Therefore, all bacteria around the area is resistant to the antibiotics and all pigs around who were infected cannot be treated with the same antibiotics.

c) Yes. low doses of antibiotics prevents the antibiotics from reaching a therapeutic level. It challenges the bacteria to develop antibiotics resistance factors (efflux pump, receptor modification, drug modification) and causes the bacteria to be resistant. Furthermore, antibiotics given in irregular or short term period can cause the drug to drop below minimum inhibitory concentration; which is required for the bacteria to be metabolically inactive. Metabolically active bacteria are capable of withstanding this condition and develop resistance to it.

Surely, more than 4 marks here.