Antibiotic resistance

Antibiotics kill certain types of bacteria. Over time, those bacteria change to develop resistance to the antibiotics. 

## Overview
Called **antibiotic resistance**, this is one of the most serious problems facing modern surgery and medicine. It is also one of the best examples of evolution in action.  As per *The Lancet*, at least 1,200,000 people died because of drug-resistant bacterial infections in 2019, more than from HIV or malaria.

## Recent trend
Antibiotic resistance spreads very quickly, far faster than microbiologists expected. "As long as new drugs keep coming, resistance is not a problem. *But there has not been a new class of antibiotics discovered since the 1980s*".  However, there is a lag-time of about eight years between discovery and possible availability for general use. The process is also extremely costly.

### Measures
The National Health Service (NHS) is encouraging  pharmaceutical companies to create new treatments by paying  up to £20 million a year for new antibiotics no matter how many are prescribed, so they so they get paid even if the drugs are just kept in reserve for special cases or an emergency. 

## Natural selection
A well-known example of natural selection in action is the development of antibiotic resistance in microorganisms. Since the discovery of penicillin in 1928 by Alexander Fleming, antibiotics have been used to fight bacterial diseases. Natural populations of bacteria contain, among their vast numbers of individual members, considerable variation in their genetic material, as the result of mutations. When exposed to antibiotics, most bacteria die quickly, but some may have mutations that make them slightly less susceptible. If the exposure to antibiotics is short, these individuals will survive the treatment.

### Prediction
In Fleming's 1945 Nobel Prize lecture he said:

## Mechanism
The mechanisms by which bacteria become antibiotic resistant are by genetic mutation and horizontal gene transfer. 

## Effects
### Surgeries
All surgery that involves cutting open the body poses massive risks of infection. Antibiotics given before and after surgery allow surgeons to do operations that would have been deadly before. Open-heart surgery is one obvious example.

### Medicine
Cancer treatments such as chemotherapy and radiotherapy damage the immune system. Antibiotics are prescribed to boost the body's natural defences. Patients with organ transplants always use drugs to suppress the immune system, otherwise it attacks the transplant. Therefore, antibiotics are used to protect the body. Without effective antibiotics, both sets of patients might die from infections which their immune systems could no longer control.

:"It's a pretty grim future, I think a lot of major surgery would be seriously threatened," said Professor Richard James of the University of Nottingham.

### World Health Organization (WHO)
The WHO has issued similar assessments:

The WHO has now listed the world's most threatening superbugs. Antibiotic resistant infections are being seen all over the world.  In 2023 it said AMR has been associated with almost 5 million deaths a year and had cost the world $100 trillion in global economic losses.

### Shareholders
About 70% of antibiotics are given to farm animals to prevent disease. Campaigners against misuse of antibiotics have raised the issue of antibiotics used in farming at company meetings, especially North American fast-food restaurant companies.  

## Examples
Given enough time, and repeated exposure to the antibiotic, a population of antibiotic-resistant bacteria will emerge. This leads to what is known as an evolutionary arms race, or co-evolution, in which bacteria continue to develop strains that are less susceptible to antibiotics, while medical researchers continue to develop new antibiotics that can kill them. A similar situation occurs with pesticide resistance in plants and insects, and with malarial resistance to quinine.

### Gonorrhoea
A man in the UK has caught the "world's worst-ever case" of gonorrhoea, a sexually-transmitted disease. The main treatment by antibiotics azithromycin and ceftriaxone has failed to cure the disease. An authority said "This is the first time a case has displayed such high-level resistance to both of these drugs and to most other commonly used antibiotics".

### Methicillin-resistant *Staphylococcus aureus*
New strains of Methicillin-resistant *Staphylococcus aureus* (MRSA) have emerged that are resistant the next generation of drugs.

### Tuberculosis
Tuberculosis (TB) is an infectious disease caused by bacteria. It is caused by various types of mycobacteria, usually *Mycobacterium tuberculosis*. The disease usually attacks the lungs, but it can also affect other parts of the body. The pathogen can travel through the air, and spread from one person to the next. Experts believe that one third of the world population is infected with *M. tuberculosis*.  New infections occur at a rate of one per second. MDR-TB is defined as resistance to the two most effective first-line TB drugs: rifampicin and isoniazid. *Extensively drug-resistant TB* is also resistant to three or more of the six classes of second-line drugs. Totally drug-resistant TB was first observed in 2003 in Italy, but not widely reported until 2012. It is resistant to all currently used drugs.

### Malaria
Malaria infections are not caused by bacteria: they are caused by a protozoan parasite injected into the blood by a mosquito. They are normally treated by a combination of two drugs, artemether-lumefantrine. In 2017 four cases occurred in Britain where the drugs have failed. The patients got the disease in Africa. A doctor said "It is an early sign and we need to take it quite seriously as it may be snowballing into something with greater impact".

## Teixobactin
*Teixobactin* is an antibiotic discovered in 2015, the first new antibiotic discovered in 40 years. It is not yet licensed for general use. It works against all gram-positive bacteria such as *Staphylococcus aureus* and against some other bacteria such as *Mycobacterium tuberculosis*.

## References