For the last 70 years, doctors have prescribed drugs known as antimicrobial agents to treat infectious diseases. These are diseases that occur due to microbes, such as bacteria, viruses, and parasites. Some of these diseases can be life-threatening.
However, the use of these drugs is now so common that some microbes have adapted and started to resist them. This is potentially dangerous because it could result in a lack of effective treatments for some diseases.
According to the Centers for Disease Control and Prevention (CDC), at least 2 million people become infected with antimicrobial-resistant bacteria in the United States every year. Around 23,000 people die as a result.
In addition, one out of every 25 hospital patients has a healthcare-associated infection (HAI) on any given day.
In this article, we look at the causes of antimicrobial drug resistance, some specific examples, and other treatment options.
Antimicrobial resistance (AMR), or drug resistance, develops when microbes, including bacteria, fungi, parasites, and viruses, no longer respond to a drug that previously treated them effectively.
AMR can lead to the following issues:
- some infections being harder to control and staying longer inside the body
- longer hospital stays, increasing the economic and social costs of infection
- a higher risk of disease spreading
- a greater chance of fatality due to infection
A significant concern is that AMR could lead to a post-antibiotic era in which antibiotics would no longer work.
This would mean that common infections and minor injuries that became straightforward to treat in the 20th century could again become deadly.
Antibiotic versus antimicrobial resistance
Distinguishing between antibiotic and antimicrobial resistance is important.
- Antibiotic resistance refers to bacteria resisting antibiotics.
- Antimicrobial resistance (AMR) describes the opposition of any microbe to the drugs that scientists created to kill them.
It is possible for AMR to develop in bacteria, but it can also originate in fungi, parasites, and viruses. This resistance could affect people with Candida, malaria, HIV, and a wide range of other conditions.
Microbes can become resistant to drugs for both biological and social reasons.
As soon as scientists introduce a new antimicrobial drug, there is a good chance that it will become ineffective at some point in time.
This is due primarily to changes occurring within the microbes.
These changes can come about in different ways:
Mutation: When microbes reproduce, genetic mutations can occur. Sometimes, this will create a microbe with genes that help it survive in the face of antimicrobial agents.
Selective pressure: Microbes that carry these resistance genes survive and replicate. The newly generated resistant microbes eventually become the dominant type.
Gene transfer: Microbes can pick up genes from other microbes. Genes conferring drug resistance can easily transfer between microbes.
Phenotypic change: Microbes can change some of their characteristics to become resistant to common antimicrobial agents.
The way in which people use antimicrobial drugs is a significant contributing factor. For example:
Inexact diagnosis: Doctors sometimes prescribe antimicrobials “just in case,” or they prescribe broad-spectrum antimicrobials when a specific drug would be more suitable. Using these medications in this way increases the risk of AMR.
Inappropriate use: If a person does not complete a course of antimicrobial drugs, some microbes may survive and develop resistance to the drug.
Resistance can also develop if people use drugs for conditions that they cannot treat. For example, people sometimes take an antibiotic for a viral infection.
Agricultural use: Using antibiotics in farm animals can promote drug resistance. Scientists have found drug-resistant bacteria in meat and food crops that have exposure to fertilizers or contaminated water. In this way, diseases that affect animals can pass to humans.
Hospital use: People who are critically ill often receive high doses of antimicrobials. This encourages the spread of AMR microbes, particularly in an environment where various diseases are present.
The United States Food and Drug Administration (FDA) point out that doctors often give antibiotics as a treatment for a sore throat. However, only 15 percent of sore throats are due to streptococcal bacteria. In many cases, antibiotics cannot cure a sore throat.
The FDA add that doctors write “tens of millions” of prescriptions for antibiotics that offer no benefit each year.
People who use these drugs are at risk of allowing AMR to develop. This could make them more likely to have a health problem in the future that will not respond to antibiotics.
Antimicrobial resistance can occur in bacteria, viruses, fungi, and parasites.
Below are some examples:
Tuberculosis (TB): This airborne lung disease results from a bacterial infection. TB was a major killer before antibiotics became available. More recently, drug-resistant forms of TB have emerged worldwide. Standard antibiotic treatments will not work against these forms of the disease.
A person who has TB that is not drug-resistant will require daily treatment with several drugs for 6 to 9 months.
Drug-resistant TB is more complex to treat. The person will need to take the drugs for a longer time, and they will need close supervision. Poor management can result in fatalities.
Methicillin-resistant Staphylococcus aureus (MRSA): This is a bacterial infection that can be fatal. People usually get MRSA when they are staying in a hospital.
In the past, it was a well-controlled infection, but now the CDC see it as a major public health concern due to antibiotic resistance.
Gonorrhea: Gonorrhea is a sexually transmitted bacterial infection that is common in the U.S. and elsewhere. Cases of drug-resistant gonorrhea have started to occur.
Now, there is only one type of drug that is still effective against the drug-resistant form of this disease.
The CDC describe drug-resistant gonorrhea as an “urgent public health threat.”
HIV: Effective antiviral treatment for HIV can now prevent this condition from becoming more severe. The treatment can make the levels of the virus undetectable, meaning that it is not transmissible.
The World Health Organization (WHO) note that if people are unable to take the drugs as they should, perhaps due to medical costs, new drug-resistant strains of the virus may appear.
Fungal infections: Candida, Aspergillus, and other fungi can lead to a range of severe infections. Candida albicans (C. albicans) is responsible for thrush, a common vaginal infection. Aspergillus can cause or worsen aspergillosis, a lung condition.
Some of these infections can have fatal consequences. There is concern that fungi are becoming increasingly resistant to antimicrobial treatments.
Malaria: Mosquitoes spread this parasitic disease, which killed around 445,000 people worldwide in 2016. In many parts of the world, drug-resistant parasites have evolved so that certain antimalarial drugs are now ineffective.
As infections stop responding to current drugs, there is an urgent need to find alternatives.
In some cases, this means using combinations of different medications, known as multiple-drug therapy.
Scientists are also looking for new forms of treatment, including different types of antibiotics and other alternatives.
What are the alternatives?
Scientists have proposed some novel ways of combating bacteria.
These include the following techniques, which researchers are investigating for the treatment of Clostridium difficile (C. difficile):
- using a virus that consumes bacteria, known as a bacteriophage, in drug form
- using monoclonal antibodies that can combat the effects of the toxins that the microbes produce
- developing vaccines to prevent infection from occurring
- fecal microbiota transplant, which involves taking good bacteria from a healthy person’s gut and transplanting them into a recipient who is lacking them
- the use of probiotics to restore the gut flora
More research into these treatments is necessary to confirm their effectiveness.
Meanwhile, experts are stressing the need for:
- doctors to prescribe antibiotics only when they are useful and necessary
- patients to use antimicrobial drugs precisely as the doctor recommends and only after a complete diagnosis
Preventing microbes from developing resistance to drugs has become as important as treating the illnesses that they cause.
The main reason for the increase in AMR appears to be the frequent and improper use of antimicrobial drugs.
Steps that people can take to help lower the risk of AMR include the following:
- Only use antimicrobial drugs when a doctor prescribes them.
- Always complete the full prescribed course, even if the symptoms have subsided. If not, the drug may only kill off the most vulnerable microbes, leaving others to survive and develop resistance.
- Never share antimicrobials with others or using leftover drugs from previous prescriptions. These medications may not be suitable for different forms of infection.
- Do not pressurize doctors into prescribing antimicrobials when they are not necessary.
- Follow good hygiene practices to prevent the spread of microbes, including washing hands thoroughly and ensuring that food preparation areas are clean.
- Get recommended vaccinations, as this will reduce the risk of needing to take medication.
AMR develops when microbes stop responding to the drugs that were previously able to kill them.
Both microbial behavior and the way in which people take antimicrobial drugs are responsible for the increase in AMR.
This resistance could be very dangerous as it could mean that it is no longer possible to treat some infections, which could lead to severe complications or even death.
Scientists are working to develop new treatments to try to counter AMR.
People can help by only using medications according to a doctor’s prescription and ensuring that they complete the full course of treatment.