Introduction to the Antibiotic Resistance Problem
- MRSA Is Putting Resistance in the News
- Humans Live with Many Pathogens
- Antibiotics Block Growth and Kill Pathogens
- Broad-Spectrum Antibiotics Also Perturb Our Microbiomes
- Antibiotic Resistance Protects Pathogens
- Antibiotic Resistance Is Widespread
- Antibiotic Resistance Is Divided into Three Types
- The Development of New Antibiotics Is Slowing
- Vaccines Block Disease
In this chapter, we define terms and provide an overview of antibiotic resistance. One of the key problems is that as a global community we have not considered antibiotics as a resource to be actively protected.1 Consequently, we use antibiotics in ways that directly lead to resistance. Changing those ways requires an understanding of antibiotic principles. We begin with a brief description of MRSA to illustrate a bacterial-based health problem.
MRSA Is Putting Resistance in the News
MRSA is the acronym for methicillin-resistant Staphylococcus aureus. (Acronyms are usually pronounced letter by letter, as in DNA; scientific names are always italicized; after an initial spelling of the entire name, the first name is often abbreviated by its first letter.) S. aureus is a small, sphere-shaped bacterium (see Figure 1-1) that causes skin boils, life-threatening pneumonia, and almost untreatable bone infections. It often spreads by skin-to-skin contact, shared personal items, and shared surfaces, such as locker-room benches. When the microbe encounters a break in the skin, it grows and releases toxins.
Figure 1-1 Staphylococcus aureus. Scanning electron micrograph of many MRSA cells at a magnification of 9,560 times.
Public Health Image Library # 7821; photo credit, Janice Haney Carr.
Sixty years ago, S. aureus was very susceptible to many antibiotics, including penicillin. Susceptibility disappeared, and the pharmaceutical industry produced increasingly potent antibiotic derivatives. Among these was methicillin, which overcame resistance to penicillin. But in 1960, one year after the introduction of methicillin, MRSA was recovered in the United States. As the resistant bacterium spread through hospitals, surgical procedures and long-term use of catheters became more dangerous. MRSA also caused pneumonia, commonly following influenza, and recently skin infections caused by MRSA captured public attention. In one newspaper account,2 pimples on a newborn baby were found to contain MRSA. Antibiotics cleared the infection; however, a month later, the father found boils on his own leg that contained MRSA. Treatment cleared the boils, but they came back. The mother developed mastitis during breast feeding that required a 2-inch incision into her breast to drain the infection. About a year later, an older child developed an MRSA boil on his back. The family is now constantly on alert for MRSA, trying to wash off the bacteria before the microbes find a break in the skin.
Community-associated MRSA has its own acronym (CA-MRSA) to distinguish it from the hospital-associated form (HA-MRSA). Many community-associated S. aureus strains are members of a group called USA300, which now accounts for half of the CA-MRSA infections. The strain causes necrotizing (flesh-eating) skin infection, pneumonia, and muscle infection. In 2005, MRSA accounted for more than 7 million cases of skin and soft tissue infection seen in outpatient departments of U.S. hospitals.3 As expected, CA-MRSA strains are moving into hospitals. In a survey of U.S. hospitals taken from 1999 through 2006, the fraction of S. aureus that was resistant to methicillin increased 90%, almost entirely from an influx of CA-MRSA.4
Although many infections tend to occur in persons having weakened immune systems, MRSA can infect anyone. For example, healthy young adults tend to be susceptible to a lethal combination of influenza and MRSA pneumonia. In Chapter 7, "Transmission of Resistant Disease," we describe occurrences of CA-MRSA infection among athletes. Fortunately, most of these dangerous CA-MRSA strains are still susceptible to several antibiotics; however, that susceptibility may soon disappear.
HA-MRSA has been a problem in hospitals for years; in many countries, it is getting worse. For example, in the United States, MRSA climbed from 22% of the S. aureus infections in 1995 to 63% in 2007 (from 1999 through 2005, it increased 14% per year).5 From 2000 to 2005, MRSA helped double the number of antibiotic-resistant infections in U.S. hospitals, which reached almost a million per year or 2.5% of hospitalizations.6 In the United States, more persons now die each year from MRSA (17,000) than from AIDS.
MRSA in hospitals is largely an infection-control problem, that is, control requires keeping the organism from spreading from one patient to another, and if possible, keeping it out of the hospital entirely. Neither is easy. For many years, the Dutch have had an aggressive screening program for incoming patients. They isolate persons who test positive for MRSA and treat them with antibiotics that still work with S. aureus. Entire wards of hospitals are closed for cleaning when an MRSA case is found, and colonized healthcare workers are sent home on paid leave until they are cleared of the bacterium. The cost is about half that required to treat MRSA blood-stream infections;7 consequently, the effort is thought to be cost-effective.
Until recently, many U.S. hospitals took a different approach: MRSA infections were considered part of the cost of doing business. Holland is a small country that can implement specialized care—the United States has a much higher incidence of MRSA. Nevertheless, in 2007, a Pittsburgh hospital reported that it had adopted the Dutch method. The hospital saved almost $1 million per year by screening patients and by insisting on more intensive hand-washing protocols for hospital staff.8 Other U.S. hospitals are reconsidering their own stance.
Individual consumers will begin to search for hospitals having low MRSA incidence. That search will be easier when hospitals publish their drug-resistant infection statistics. Some states now require reporting of MRSA to health departments; consequently, the numbers are being collected. As an added incentive for MRSA control, some insurance carriers refuse to cover hospital costs when a patient contracts MRSA while there. Hospitals have responded by setting up antibiotic oversight committees to help keep resistance under control.