JUDY WOODRUFF: Next: the mounting worries and public health concerns over the rise of drug-resistant bacteria.That's the subject of tonight's episode of FRONTLINE.

To tell the story, the program examines three notable cases, including that of Addie Rerecich, an 11-year-old girl in Tucson.After complaining of a nagging pain in her hip, she ended up fighting for her life in the hospital in 2011.Here's an excerpt, beginning with her mother's recollection.

TONYA RERECICH, mother: I thought, well, you know, she's just finishing up softball.She had been tothe track meet, you know, oh, kind of, well, it could have been an injury.

I gave her some ibuprofen.As the night wore on, her pain got worse. She didn't sleep much that night, woke me up a couple times asking if she could take a hot bath or have another ibuprofen.

NARRATOR: The next morning, Tonya Rerecich, a nurse for 16 years, took Addie to a local hospital, where they said she had symptoms of a virus.But over the next two days, the pain spread and the fever gotworse.

TONYA RERECICH: I was afraid.At that point, I remember being very afraid. And so I packed a bag, andwe went to another hospital that had -- specialized in children's care.

I remember thinking, she looks bad.This is bad.Something's really, really wrong.They put her on antibiotics.Her blood pressure was dropping.They were making space in the ICU for her.The next morning, she need oxygen via mask.They looked at part of her lungs and diagnosed with her pneumonia.

I remember sitting there watching the sun come up and thinking, how did she get so sick?How did this happen so fast?

SEAN ELLIOTT, specialist: I met Addie in a hospital bed in the intensive care unit.She was lying there breathing quickly.She was scared.She had little infected boils all over her body.What really looked most likely when I saw her was a staph bacteria causing septic shock.And Addie fit a pattern that I recognized with community associated MRSA.

JUDY WOODRUFF: Ray Suarez picks up more of the story from there.

RAY SUAREZ: Journalist David Hoffman investigated this for FRONTLINE. And he joins me now. And, David, in your story, we see yet more of this young girl's suffering.Did any of the conventional drugs available ever answer Addie's infections?

DAVID HOFFMAN, FRONTLINE: No. This courageous girl went through a real nightmarish odyssey.And in the end, she had to suffer surgery to remove the infection, because the bacteria were resistant to all of the antibiotics we have on the shelf.

RAY SUAREZ: What does this story tell us about the race between infection and antibiotics, the drugs we have got available to fight them?

DAVID HOFFMAN: Well, I think that one thing it tells us is, this could happen to any of us.And we oftentimes think about something like antibiotic resistance as a problem that other people might have or it could happen to somebody else.

But we as a society have a looming problem that some of these bacteria, some of the harmful ones, are becoming resistant to our last-resort, very best antibiotics.

RAY SUAREZ: We ought to talk more about what becoming resistant means.Do they evolve?Do they gradually develop a tolerance for what we have been hitting them with in human beings' systems?

DAVID HOFFMAN: Evolution drives everything, and it's relentless, constant.And these bacteria have hadyears and years of being bombarded with our antibiotics, in large measure because we overused them, because we took too many of them.But, as they evolve, they think of defense mechanisms to fight back.

And our documentary film is partially about a group of bacteria known as gram-negative bacteria that can be very dangerous if you get an infection.But one of the things that's been discovered about some of these is that they have developed kind of an armor, a hard shell, in which they can defend themselves against the antibiotics, even the best ones.

RAY SUAREZ: How are the drug companies, who, after all, produce the drugs that are becoming increasingly unable to treat these infections, responding to this threat?

DAVID HOFFMAN: Well, this is a tough time, because in the golden age of antibiotic drug development, these companies developed literally dozens and dozens of new ones.And when one antibiotic stopped working, we always had the promise of new ones.

But a couple things happened.First of all, the science got harder.And, also, the economics changed.Many of these drug companies will have to spend a billion dollars as an investment in a new drug.And theylook at the question of an antibiotic, which you take briefly, that's how you're supposed to use it, and then stop taking, and compare the return on investment to their billion dollars with, say, a drug for a chronic disease, like a cholesterol drug, well, they have chosen to invest in the chronic disease.

It's a strict choice about capitalism, about the market.In some ways, the market isn't really helping us here, because the choices these companies are making are to develop the big blockbuster drugs that people have to take for life.So they have cut back on antibiotic development, just at a time when resistance seems to be rising.

RAY SUAREZ: Well, you mentioned drugs that are designed to only be taken for a short period of time.Isn't part of the problem that too many of us take too many antibiotics too often?

DAVID HOFFMAN: It's been a problem throughout the 70-year history of the antibiotic age.

Alexander Fleming, who first came up with penicillin, warned us in his Nobel Prize speech in 1945 against overuse.And, today, we're seeing some of the results of overuse.There was a study out just last week that found that the large number of people that went to doctors in emergency rooms for sore throats, of the whole group, about 10 percent of them had a legitimate need for an antibiotic, and about 50 percent of them actually got antibiotics.

RAY SUAREZ: But do we -- are we ready to tell people, no, you can't have them; just suffer through this infection until you kick it?

DAVID HOFFMAN: Well, there are plenty of cases, viruses and other ailments that people have, where antibiotics won't do any good.

And a lot of estimates suggest that at least half of the antibiotics that we give to humans are wrongly prescribed or the doses are wrong.So, yes, we need some better stewardship.We ought to take care of these medicines, rather than use them recklessly.

RAY SUAREZ: A couple of the people that you spoke to talked about a post-antibiotic world of medicine.And given some of the horrifying infections you show us in the course of the program, what does a post-antibiotic world look like, where some of our major weapons don't work anymore?

DAVID HOFFMAN: Well, Ray, all you have to do is look at the age before antibiotics.

I think we, as our generation, has forgotten what it was like in the period before World War II, when a simple infection could oftentimes lead to someone's death.And I guess the question we face is, do wewant to go back to that age?

You only have to look at a time when infections were dealt with automatically by surgery.There were noantibiotics.And when antibiotics were invented and when they came along after World War II, consider what they did for modern medicine.We have sophisticated surgeries today like transplants because of antibiotics.

We have cancer treatments that are only successful because of antibiotics.So a post-antibiotic age won't only mean the danger of infection, but a lot of things that we have innovated in medicine, a lot ofthe most important therapies won't be available if we don't have antibiotics.

RAY SUAREZ: And, very quickly, are we close to that terrible world?

DAVID HOFFMAN: I don't think that anybody knows.But the trend is turning negative.We need to do something about it.

RAY SUAREZ: David Hoffman from tonight's FRONTLINE, thanks a lot.

DAVID HOFFMAN: Thank you.