How Does Salmonella Get Into Eggs?

On Friday the Food and Drug Administration announced they found salmonella in chicken feed that was used at two Iowa farms where tainted eggs have been traced. An estimated 2,400 people have been sickened from the eggs and more than 550 million eggs have been recalled since early August. Even if investigators have indeed found the salmonella source, you may wonder, how can the bacteria get inside the hard shell of an egg? Chickens get doses of salmonella bacteria (of which there are 2,300 kinds) from their environment, which is easily contaminated by rodents, birds and flies. These carriers deliver the bacteria to all types of farms -- regardless of whether they're conventional, organic or free-range.
This article related to Biology because it has to do with the salmonella baceria infecting chicken eggs.
It is important to us because it informs us that this bacteria is found in eggs also, which is a common food eaten by many people. By letting us know what could potentially be in our food, we could take protective measures to ensure our health.