Antibiotic susceptibility is a metric for determining how antibiotic-resistant a population of organisms is. Some people are highly susceptible, while others are highly resistant, and the goal is to find a treatment that kills the majority of the organisms in a given population. The immune system is much more capable of attacking the infection and killing any remaining individuals once the bulk of the infection has been addressed.
Antibiotic susceptibility testing can be done using a variety of methods. Growing a population of bacteria in culture and adding small discs coated with various antibiotics is one of the most basic methods. If the organisms are sensitive to a particular medication, a dead zone will form around the disc as bacterial growth is slowed. Doctors can use this information to determine which medications they will use to treat a patient.
Antibiotic susceptibility testing has a wide range of applications. These tests can be used in the development of new antibiotic medications to identify organisms that the drugs should target. They can also be used to test susceptibility in vitro rather than on the patient in the evaluation of a patient with a persistent infection, allowing doctors to prescribe an effective medication as quickly as possible. Antibiotic susceptibility research is also used to better understand how bacteria evolve and respond to antibiotic exposure.
Antibiotic susceptibility is extremely low in some bacteria. This can be a natural trait, and as antibiotics are used and organisms are exposed to them, the organisms with the highest levels of resistance will survive. These go on to reproduce, resulting in an increase in resistance in the population as a whole. Antibiotic resistance is a major concern in medical treatment around the world, particularly in infections acquired in hospitals, where patients are already weak and less capable of fighting infection, and in immunocompromised patients, such as AIDS patients.
Even in organisms that are known to have high antibiotic susceptibility, a few individuals have higher resistance. It is critical to finish antibiotic courses in order to reduce the likelihood of these individuals surviving, thereby keeping the population vulnerable and making it easier to treat infections caused by these organisms. If people do not finish antibiotics or do not follow administration instructions, they risk contributing to the development of antibiotic resistance in the population, making those drugs less effective for preventing infection recurrence in themselves and other patients in the future.