How do antibiotics kill bacteria?

Updated February 21, 2017

Antibiotics are medicines used that kill or inhibit bacteria in patients without harming the patient. Some antibiotics are made from natural sources, such as Penicillin and other antibiotics are made from synthetic sources in laboratories. Different antibiotics can be classified into two different groups. The two groups are bacteriostatic and bacteriocidal. The two groups of antibiotics work in different ways.

Bacteriostatic Antibiotics

Antibiotics that are classified in the bacteriostatic group don't actually kill bacteria. Bacteriostatic antibiotics inhibit the growth of bacteria. Inhibiting the growth of bacteria, allows the patients' immune system to fight off the existing bacteria without becoming overwhelmed with the growth of more bacteria.

Bacteriocidal Antibiotics

Antibiotics that are classified in the bacteriocidal group do kill bacteria. Bacteriocidal antibiotics are considered more affective because they do kill all of the bacteria instead of leaving some bacteria remaining for the patients' immune system to fight off. Patients that have weak immune systems may have trouble fighting off bacteria. For these patients, bacteriocidal antibiotics are especially beneficial.

How Antibiotics Work

There are several different ways that antibiotics work to kill or inhibit bacteria. Some antibiotics kill bacteria by attacking the outer cell wall of the bacteria. Some antibiotics kill bacteria by attacking the inner membrane of the bacteria cell. Some antibiotics kill bacteria by attacking the chemical pathways bacteria require for survival. Some antibiotics inhibit bacteria growth by attacking the chemical pathways bacteria require in order to reproduce.

Antibiotic Resistance

Sometimes bacteria develop a resistance to certain antibiotics. When bacteria survive exposure to an antibiotic, the bacteria become stronger against and more likely to survive that antibiotic in the future. The bacteria passes the resistance gene when it reproduces. Eventually, the resistant gene can be passed to large numbers of bacteria, producing an antibiotic-resistant strain of bacteria. Antibiotic resistance is exasperated by patients who don't finish their prescription of antibiotics, not fully killing the bacteria and encouraging bacteria resistance in surviving bacteria. When bacteria develops a resistance to a certain antibiotic and stops being affective, doctors must start using a different antibiotic.

Antibiotics are not Selective in Which Bacteria is Killed

While antibiotics help a patient by killing harmful bacteria, the medicine often kills good bacteria, also. Antibiotics are not selective in what bacteria that is killed. The body has several species of good bacteria that are helpful to the body. For instance, the good bacteria acidophilus is naturally found in the body and aids digestion. Because antibiotics kill acidophilus, some doctors suggest that patients taking antibiotics, take an acidophilus supplement at the same time.


Antibiotics are a useful and life-saving medicine in the health care industry when used against bacterial infections. Antibiotics are not affective against viral infections.

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