Drug resistance refers to the ability of a microorganism, such as a bacterium, virus, fungus, or parasite, to resist an antimicrobial medicine that had previously been effective against it. Drug resistance develops as a result of the use of antimicrobials and can be accelerated by the improper use of antimicrobials, such as failing to complete a prescribed course of treatment or the use of antimicrobials against diseases for which they are known to be ineffective (for example, using antibiotics to treat a virus).
Antimicrobial resistance threatens to reverse the gains made by medicine against infectious disease in the last 60 years and is an international problem that can threaten the lives of patients, hamper the control of infectious disease, and increase health care costs. In addition, as the result of modern means of transportation and the ability of people to move all over the world, antimicrobial resistance is not a problem that can be contained in any one country; instead, movement of an infected person can easily spread drug-resistant microbes from one country to another.
Bacteria, viruses, parasites, and other microbes are living organizations that mutate rapidly and evolve over time; the process of natural selection ensures that the microbes that are best adapted to their environment will survive, and those that are resistant to available antibiotics are thus favored for survival. This evolution is a normal process of nature but becomes a matter of concern in terms of medicine because this process of evolution helps create microbes that are resistant to medicines effectively used against them in the past. Consider the example of a person with a bacterial infection who takes a prescribed antibiotic to combat the infection. Some bacteria will be quickly killed by the antibiotic, but others may have mutated and are resistant to it (that is, the antibiotic does not kill them, or kills them more slowly). If those bacteria survive the antibiotic treatment, they will reproduce and very likely pass the mutation on to their descendants, and in this way a large population of antibiotic-resistant bacteria may be created. When these bacteria infect a new person, existing antibiotics may not be effective in treating this patient, who may suffer serious illness or die as a result.
One of the great success stories of modern medicine is the development of antibiotics such as penicillin, sulfa drugs, and tetracycline to combat common infectious diseases. In the mid-20th century, many believed that modern medicine had conquered formerly dreaded diseases such as tuberculosis and pneumonia, while also bringing common infections such as strep throat and ear infections readily under control. However, as a result of the normal course of evolution, as the use of antimicrobials increased, so did the emergence of strains of resistant microbes. Originally, this was less of a problem because numerous types of antimicrobial drugs were available to treat infections, and if one was no longer effective, a different drug could be substituted. However, continued use and abuse of antibiotics has created a situation in which common bacteria are resistant to numerous drugs, complicating the process of treating patients.
The evolution of drug-resistant bacteria is a natural process, but some behaviors encourage that process. One is failing to complete a prescribed course of antibiotics; this behavior allows bacteria that are resistant to the treatment to survive and multiply. Another is the overuse and inappropriate use of antibiotics; even appropriate use of antibiotics aids the process of breeding drug-resistant bacteria, but overuse and inappropriate use encourages this process without providing any benefit to the patient. Some researchers also believe that widespread use of antibiotics in agriculture (for instance, adding antibiotics to animal feed) also encourages the growth of resistant microbes that can infect humans.
Tuberculosis (TB), a disease that once seemed to be nearly conquered by antibiotics, has become a health threat once again because of the emergence of drug-resistant strains of TB. Multidrug-resistant TB (MDR-TB) refers to resistance to the most commonly used (first-line) TB drugs, rifampicin and isoniazid. It can be treated with other drugs, but it has difficulties, including the need for a longer course of treatment and the fact that the less common drugs are generally more expensive and have more side effects than the first-line drugs. The World Health Organization (WHO) estimates that about 440,000 new cases of MDR-TB occur each year, and that at least 150,000 deaths annually are caused by MDR-TB. An even more serious concern is extensively drug-resistant tuberculosis (XDR-TB), which is resistant not only to the first-line drugs but also to any fluoroquinolone and to at least one of capreomycin, kanamycin, and amikacin. According to the WHO, extensively drug-resistant tuberculosis had been reported in 64 countries as of 2012.
Staphylococcus aureus (staph) is a common type of bacteria often found on people's skin and in their noses; however, staph can also cause illnesses ranging from boils and pimples to meningitis and sepsis. When penicillin was first introduced, it was highly effective against staph infection, but today many strains of staph are resistant to penicillin. Other drugs effective against staph have been developed, but a particularly dangerous strain known as methicillin-resistant Staphylococcus aureus (MRSA) has become increasingly common and has been particularly identified as responsible for many hospital-acquired infections. The WHO estimates that worldwide, a high percentage of infections acquired within hospitals are caused by drug-resistant organisms such as MRSA and vancomycin-resistant Enterococci. In the United States, the Centers for Disease Control and Prevention (CDC) estimate that the proportion of health care-related staph infections related to MRSA increased rapidly from the 1970s to the early 21st century; in 1974, 2 percent of staph infections in intensive care units were caused by MRSA, and this proportion grew to 22 percent in 1995 and 64 percent in 2004. However, increased attention to infection control has caused the number of MRSA infections to decline since then; for instance, a 34 percent decrease in MRSA infections in hospitalized patients was observed between 2005 and 2008.
Shigellosis is an infectious disease characterized by severe and often bloody diarrhea, high fever, and cramping; it is caused by the Shigella bacteria. The WHO estimates that shigellosis causes over 120 million cases of severe dysentery each year, primarily in developing countries and in children under five years of age; about 1.1 million people die annually from shigellosis, about 60 percent of whom are children younger than five. Antibiotic-resistant strains of shigellosis are a matter of increasing concern in countries where the disease is common. For instance, a WHO study in several Asian countries in 2000–04 found that a majority of Shigella isolates were resistant to cotrimoxazole and amoxicillin, and a 2005 study reported that 95 percent of the isolates of two major strains of Shigella, S. sonnei and S. flexneri, were resistant to tetracycline and cotrimoxazole, and 95 percent of the S. flexneri isolates were also resistant to tetracycline and chloramphenicol. The WHO currently recommends only ciprofloxacin for treatment of shigellosis, because of increasing resistance to other antibiotics, but ciprofloxacin resistance is also becoming a problem.
Malaria is caused by infection with a parasite transmitted from person to person through the bite of an anopheles mosquito; symptoms include fever and chills, anemia, and flu-like symptoms. Malaria remains a major health threat in many tropical countries; the CDC estimates that 300–500 million cases occur each year, and over 1 million people annually die from the disease. Drug resistance is becoming an increasing problem with malaria: the WHO found in 2010 that three of the five strains of malaria known to infect humans were partially drug resistant, and some had cross-resistance (resistance to multiple drugs with similar modes of action or that come from the same chemical family) or multidrug resistance. Consequences already recorded for drug-resistant malaria include longer periods of illness, increased mortality, increased cost of treatment, and increased transmission of the disease. In addition, it is feared that ineffective treatment in the public sector (because standard drug therapies fail) will push more patients to the unregulated private sector, where they may be exposed to substandard care as well as a course of treatment known to increase drug resistance.
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When disease-causing microorganisms—bacteria, fungi, parasites, viruses—develop the ability to withstand a particular medication, they are said to b
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(nucleic-acid-based approaches for bacteria) The traditional, culture-based methods for detecting antibiotic resistance in bacteria are suitable mai