What are superbacteria?
Superbacteria are organisms that have developed resistance to many antibiotic drugs. Infections caused by these bacteria can be extremely difficult to treat, as some have become resistant to all antibiotics that were once effective against them. Because resistance can spread from one bacterium to another, resistant strains of many different types of bacteria have emerged.
Superbacteria have become a serious health threat worldwide; antibiotic-resistant strains are present on every continent, including Antarctica. The incidence of illness caused by drug-resistant bacteria is increasing dramatically around the world. Resistant strains of disease-causing bacteria, originally found primarily in hospitals, have now moved beyond health care facilities and into communities.
When bacteria are exposed to an antibiotic, most of them will die. However, a few bacteria may acquire changes in their DNA (deoxyribonucleic acid) that allow them to survive in the presence of the drug. These bacteria will multiply, creating a drug-resistant group. This vertical transmission (that is, the method of passing resistance genes) requires time for resistance-causing mutations to arise and stays within the same type of bacteria.
The rapid spread of multiple resistance genes among species of bacteria occurs through a second method of gene transfer: horizontal transmission. Bacteria often carry their antibiotic resistance genes on bits of DNA called plasmids, which are commonly passed between bacteria. One plasmid can contain genes for resistance to numerous different antibiotics. Bacteria that receive such a plasmid will become resistant to multiple antibiotics in one rapid event. They can then spread this resistance even further when they multiply.
The widespread use of antibiotics in medicine and agriculture has led to the emergence and spread of superbacteria. Frequent exposure of bacteria to antibiotics increases the likelihood that they will develop resistance. Hospitals provide ideal conditions for bacteria to acquire resistance, because antibiotics are often used liberally and because many species of disease-causing bacteria are present.
Drug-resistant bacteria also arise on farms that produce meat and poultry, where antibiotics are routinely given to healthy animals to prevent disease and to promote growth. Incomplete treatment of pathogens with antibiotics can also promote resistance. When a person stops taking prescribed antibiotics before all bacteria are eliminated, the remaining bacteria may become resistant.
Staph infections. Methicillin-resistant Staphylococcus aureus (MRSA) causes skin and soft tissue infections, which can be invasive and life-threatening. MRSA is usually resistant to aminoglycosides, macrolides, tetracycline, chloramphenicol, lincosamides, and methicillin. MRSA infection is a major public health problem. According to the Centers for Disease Control and Prevention (CDC), MRSA infection in 2008 caused life-threatening illness in 90,000 people and 15,250 deaths in the United States alone.
Tuberculosis. Nearly one-third of the world’s population is infected with Mycobacterium tuberculosis, the bacterium that causes the lung disease tuberculosis (TB). About ten percent of those infected will develop TB. The rise of antibiotic resistance now threatens the only treatment for TB, which is antibiotic therapy. Strains of M. tuberculosis that are resistant to a minimum of one antibiotic have been documented in every country surveyed by the World Health Organization. Multidrug-resistant TB (MDR TB) is caused by strains of M. tuberculosis that are resistant to both isoniazid and rifampicine, the two most effective anti-TB drugs.
Opportunistic infections. Persons with compromised immune systems are vulnerable to infection by organisms that are normally harmless in healthy people. Acquired in hospitals, opportunistic infections can be life-threatening without appropriate antibiotic treatment. Drug-resistant strains of the bacteria responsible for these infections pose a growing threat to hospitalized persons. The CDC estimates that annually, two million persons in the United States get some sort of infection while in the hospital; 70 percent of the bacteria that cause these infections are resistant to a minimum of one antibiotic typically used to treat them.
Strains of Klebsiella pneumoniae have developed resistance to carbapenems, one of the few classes of antibiotics effective against these gram-negative bacteria. Enterobacter variants are also carbapenem-resistant, and they are resistant to all penicillin derivatives and cephalosporins. Enterococcus faecium has developed strains that are resistant to both ampicillin and vancomycin. Pan-resistant strains of Pseudomonas aeruginosa and Acinetobacter baumannii are no longer treatable with any known antibiotics.
Superbacteria present a serious global threat to human health. The worldwide spread of antibiotic resistance jeopardizes the usefulness of antibiotics in the treatment of bacterial diseases. Health care providers increasingly face the challenge of treating infections for which few or no effective antibiotics exist. People with resistant infections face longer hospital stays, more severe illness, and an increased chance of death from certain diseases. The resulting costs are high, both in terms of health care dollars and human lives. Solutions will require global efforts to reduce overuse and misuse of antibiotics, to prevent the spread of resistant organisms, and to develop new antibiotic agents.
Groopman, Jerome. “Superbugs.” The New Yorker 84 (2008): 46-55. Recounts outbreaks of drug-resistant bacteria and discusses the causes and economic impact of multidrug resistance.
Klevens, R. M., et al. “Invasive Methicillin-Resistant Staphylococcus aureus Infections in the United States.” Journal of the American Medical Association 298 (2007): 1761-1763. A study that examines the prevalence of MRSA infection in the United States.
Muto, C. A., et al. “SHEA Guideline for Preventing Nosocomial Transmission of Staphylococcus aureus and Enterococcus.” Infection Control and Hospital Epidemiology 24 (2003): 362-386. Presents evidence-based recommendations for preventing the spread of antibiotic-resistant bacteria in hospitals.
Nikaido, Hiroshi. “Multidrug Resistance in Bacteria.” Annual Review of Biochemistry 78 (2009): 119-146. Review article describes the molecular mechanisms of antibiotic resistance in bacteria.
Sachs, Jessica Snyder. Good Germs, Bad Germs: Health and Survival in a Bacterial World. New York: Hill and Wang, 2008. Describes for general readers the nature and scope of antibiotic resistance and discusses the practices that have led to drug-resistant bacteria.
Sharma, Surendra, and Alladi Mohan. “Multidrug-Resistant Tuberculosis: A Menace that Threatens to Destabilize Tuberculosis Control.” Chest 130 (2006): 261-272. A comprehensive review of drug-resistant tuberculosis worldwide, including its epidemiology, molecular mechanisms, diagnosis, and treatment.