Directions: Read article and write a paragraph summary (at least 5 sentences) explaining:

“How does natural selection result in antibiotic resistance?”

Natural Selection in Antibiotics

Natural selection is a rather simple idea. In a group of organisms, let's a say a litter of newborn wolf cubs, there will be some variation from cub to cub even though all the cubs have the same mother and father. The differences are caused by random mutations of the wolves' DNA. Some of the changes may make the wolf cubs better hunters and better survivors, and some of the changes may make them poorer hunters and poorer survivors

For example, one cub may be born with larger teeth. This wolf may be a good hunter and survive to pass the genes for larger teeth on to the next generation of wolves. Another wolf cub may have smaller teeth. This wolf may be a poorer hunter, and may not live long enough to reproduce. Then the genes for smaller teeth will not be passed on to the next generation of wolves. This means that in time, most wolves will have larger teeth. In fact, if you look in a wolf's mouth, you will see its teeth are very large, but we don't recommend you get too close to the mouth of any wild carnivore!

Charles Darwin helped develop this idea in the 1800s. He studied ecosystems around the world and was intrigued by the way animals and plants always had just the right features to live in their own environments. In the Galapagos Islands off the western coast of South America, he found lots of different species of finches—small seed-eating birds. On every island he found the finches had different kinds of beaks. The finches of each island had beaks suited to breaking open the particular seeds that were found there. The variation of beak type clearly indicated an adaptation to different types of food available on the different islands.

Natural selection doesn't just affect big animals like birds and wolves. It also affects microbes, and this is not always a good thing. Our use of antibiotics can sometimes cause the evolution of bacteria that resist antibiotics. This is how it works: There are many many bacteria in a person who suffers from a bacterial disease. Some of them will be more resistant to antibiotics than others, because of random mutations. If the patient is treated with antibiotics, the antibiotics may not kill all the bacteria, but only those bacteria that are most susceptible to the antibiotic. The most resistant bacteria are left behind. When the surviving bacteria reproduce, the genes for resistance will be passed on to the entire next generation of bacteria. In short, sometimes antibiotics only kill the weak bacteria, leaving the stronger nastier ones behind.

This happens when a patient stops taking antibiotics before the doctor says to do so. This also happens when antibiotics are given for diseases that aren't caused by bacteria, such as colds and flu!!

http://www.chemheritage.org/EducationalServices/pharm/antibiot/activity/reslab.htm