Last reviewed by the Faculty of Harvard Medical School on August 9, 2012
By Howard LeWine, M.D.
Brigham and Women's Hospital
Bacteria and other microorganisms that cause infections are remarkably resilient and can develop ways to survive drugs meant to kill or weaken them. This is called antibiotic resistance, also known as antimicrobial resistance or drug resistance. It is due largely to the increasing use of antibiotics.
Today, almost all important bacterial infections in the United States and throughout the world are becoming resistant. Antibiotic resistance has been called one of the world's most pressing public health problems. The smart use of antibiotics is the key to controlling the spread of resistance.
In the past, doctors routinely treated bronchitis and ear infections with antibiotics. Now it seems that many doctors say they are not needed. What's changed?
During the past 50 years, doctors have been able to successfully treat bacterial infections that previously killed thousands of otherwise healthy people by prescribing antibiotics. Doctors have always been concerned that a bacterial infection could become overwhelming and fatal, if not treated. So they preferred to prescribe an antibiotic rather than wait to see if the condition got better on its own or not.
Because some sore throats, bronchitis and ear infections were caused by bacteria, we thought we were helping people with these conditions get better faster. Doctors became very used to treating these and many disorders with antibiotics. Then patients started expecting them. You could often hear people say, "I need to see my doctor to get an antibiotic." The overuse of antibiotics became the norm.
Looking back, no medical studies had been done to determine which conditions needed an antibiotic and which got better on their own. But based on studies that we have now, it turns out that most cases of sore throat (those not caused by strep), bronchitis, and sinus and ear infections will get better on their own. Antibiotics are only needed when the symptoms do not improve and a bacterial infection is most likely causing the problem.
I always thought that green or yellow mucous meant that I definitely have a bacterial infection. Why isn't this true any more?
It's not bacteria that produce the green color. When mucous or phlegm turns green, it means that white cells are actively fighting the infection. The green color comes from a protein called myeloperoxidase inside the white blood cells.
Bacterial infections increase production and activity of the myeloperoxidase-containing white blood cells compared with infections caused by viruses. Sometimes inflammation without an infection due to allergies can cause sputum to have a greenish color.
For certain chronic lung diseases, a change from clear to green sputum indicates the need for an antibiotic. In otherwise healthy people, a cough that produces a little green phlegm does not automatically require an antibiotic. Yellow phlegm is an even less reliable way to determine bacterial infections.
Even though my illness may not be caused by a bacterial infection, what's the harm in taking an antibiotic?
There are several ways antibiotics can harm you.
- Any medication can cause an allergic reaction, but reactions to antibiotics are very common and can be very serious — even life threatening.
- Antibiotics kill many of the "good" bacteria that live in our lower intestine. This upsets the balance and can lead to overgrowth of bacteria called Clostridium difficile. These bacteria produce a toxin that can cause severe diarrhea and sometimes a sudden and severe colitis.
- Many women develop vaginal yeast infections whenever they take antibiotics. The cause is similar to what happens with C. difficile in the colon. Yeast can multiply quickly as the antibiotic kills the "normal" bacteria living in the vagina.
- The overuse of antibiotics contributes to the ever-increasing resistance bacteria develop to antibiotics. Bacteria can evolve or change faster than new antibiotics can be developed and then overused. This means they find ways to survive and become less susceptible to antibiotics' effectiveness.
Why should I care about antibiotic resistance?
If you take dicloxacillin (a type of penicillin) to treat a Staph bacterial infection, the antibiotic might not kill all of the Staph. If a few Staph are resistant, they will survive and multiply. And the new generations of Staph will all carry the changes that make them resistant to the dicloxacillin antibiotic.
Over the last 20 years, many types of bacteria have become resistant to commonly used antibiotics. So, bacterial infections often don't respond to antibiotic treatment when it is really needed. These antibiotic-resistant bacteria can jump from one person to the next. Many people can get colonized — meaning that these bacteria reside on their skin or inside their lower intestines.
Only a handful of people who get colonized will actually get an infection. But if they do get sick, then this new strain of bacteria will be much harder and more expensive to treat. People don't become resistant to an antibiotic. The bacteria do. Some bacteria become resistant to many drugs and rarely some don't respond to any of the antibiotics currently approved. A person who is colonized with multi-drug resistant bacteria can pass this on to someone else who may develop a severe infection.
Antibiotics have been around for over 60 years. How come antibiotic resistance has become such a problem recently?
There are three main reasons why antibiotic resistance has become more prevalent:
- The over use of antibiotics promotes the emergence of more strains of resistant bacteria.
- Drug companies have been very successful at discovering drugs that can attack many different species of bacteria. They are called broad-spectrum antibiotics. When a doctor suspects that a person has a bacterial infection but is not sure which specific type is causing the infection, prescribing a broad-spectrum antibiotic increases the probability that the drug will be effective. However, these antibiotics will kill a lot of bacteria that live with us but don't harm us. Some of these will be resistant to the drug. The resistant ones survive and thrive. They take over and stay around even after the antibiotic is discontinued.
- People with chronic diseases and impaired immune systems are living longer. Most healthy people who become colonized with a resistant bacterial strain will eventually fight it off using their immune system. But for people with chronic diseases and impaired immune systems, the resistant bacteria are more likely to hang around.
I keep hearing about MRSA. What is it? Why is it so dangerous?
MRSA is short for methicillin resistant Staphylococcus aureus. Originally good old penicillin killed all strains of Staph aureus. Many years ago, however, a strain of Staph became resistant to penicillin. Methicillin was developed as the "cure" for penicillin-resistant Staph.
Methicillin and similar drugs originally worked against almost all Staph infections. But as more methicillin needed to be used, multiple strains of Staph became resistant to all the penicillins and other types of antibiotics as well.
Staph bacteria are all around us and live on our skin. If they get under the skin and multiply, they will usually cause a small abscess. However, Staph bacteria can infect any organ in the body. If they get into the blood stream, they can affect many organs at the same time.
Staph infections can potentially be very serious and even fatal — even those that can be treated with the older antibiotics. But some strains of MRSA are not only resistant to most commonly used antibiotics, but have evolved into bacteria with other threatening features. This makes them especially dangerous.
Some MRSA strains are especially hardy. Normally white blood cells work in concert with an antibiotic to destroy bacteria. The hardy MRSA actually sense danger and attack the white blood cells, destroying them before the MRSA is destroyed.
Also some MRSA strains have developed ways to spread more easily from one person to the next.
Are there other bacteria that are resistant to antibiotics?
Unfortunately, the answer is yes. And the list keeps getting longer. Despite the great progress science has made in discovering new antibiotics to treat resistant strains, some bacteria have consistently stayed ahead of the science. In addition to MRSA, other bacteria that have developed resistance include Enterococcus, which causes blood, kidney and heart valve infections, and Clostridium difficile, which causes antibiotic-induced colitis and diarrhea.
How can I prevent getting MRSA and other infections with resistant bacteria?
The best prevention is frequent hand washing with soap and water or an alcohol-based hand cleanser. If you or your child is active in a team sport, it is especially important to wash your workout clothes and uniforms after each use.
Don't ignore small cuts or breaks in the skin. Rinse them thoroughly. If you develop increasing redness, swelling or pain around a cut, promptly seek medical advice.
When visiting a person who is in the hospital or nursing home, thoroughly wash your hands before and after your visit. Strictly follow any instructions posted outside the room regarding contact precautions. You may need to wear protective gloves and a full gown during the visit. When leaving the room, leave the gloves and gown inside the room in specially marked containers.
We all need to use antibiotics more appropriately. You can help your doctor by asking if you are likely to get better just as fast without taking one. If your doctor says you don't need an antibiotic ask what you can do to decrease your symptoms while your body is healing. Don't save antibiotics and start them again without specific instructions from your doctor. Don't share antibiotics with family or friends.
Howard LeWine, M.D. is chief editor of Internet Publishing, Harvard Health Publications. He is a clinical instructor of medicine at Harvard Medical School and Brigham and Women's Hospital. Dr. LeWine has been a primary care internist and teacher of internal medicine since 1978.