What are antibiotics, types and main examples

What are antibiotics, types and main examples

What are antibiotics?

Antibiotics are medications specifically used to eliminate bacteria without damaging our body cells. There are several different types of antibiotics to have an effect on all types of bacteria harmful to our body. They are medications that work exclusively on bacteria and are not capable of eliminating viruses and fungi.

The first antibiotic discovered was penicillin. It was discovered by accident by British microbiologist Alexander Fleming. He was doing studies looking for a way to avoid bacterial infections.

He took a vacation in 1928 and forgot to refrigerate some of the bacterial specimen plates. Some time later, when he returned to work, he found the sample contaminated with mold. When he was going to discard the sample, a colleague visited him and asked about the research.

Fleming used the samples he had to explain the work and noticed that in one of them there was a clear circle around the mold that was contaminating the bacteria, indicating that it produced a bactericidal substance.

After taking samples of the mold and doing more tests, penicillin, the first existing antibiotic, was produced.

In this article you will find the following information:

  1. How do they work?
  2. Mechanisms of Action
  3. Antibiotic classification
  4. The most used
  5. How to know which antibiotic is most suitable?
  6. Bacteria
  7. Resistances
  8. Super bacteria
  9. Emergency antibiotics
  10. Side effects
  11. Antibiotic makes you fat?
  12. Drug interactions
  13. How and when to use correctly


How do they work?

Bacteria invade the host’s body and use the body’s resources to reproduce, doubling in quantity with each reproduction cycle, which can last a few hours or a few minutes.

When they reach a certain number, they begin to damage the body, modifying the environment around them. The immune system is then activated and wages a battle with the bacteria, seeking to eliminate the infection.

Often the battle can last for days and the body is not always able to win. When this happens, bacteria kill the host.

Sometimes the body can even get rid of the bacteria, but depending on how strong the immune system or the bacteria are, there can be damage to the body. That’s where antibiotics come in: they help the body.

Each type of antibiotic has a different effect and not every bacterium is sensitive to every antibiotic. Some types work by killing bacteria and some prevent them from reproducing, preventing them from multiplying and conquering the body. The immune system is then able to terminate the few surviving bacteria and those that are no longer reproducing.

Mechanisms of Action

Modern antibiotics can be divided into two types, depending on how they work. Are they:


Bactericides are antibiotics that kill bacteria. They can do this in a number of ways, reducing their numbers drastically and making it easier for the immune system.

There are several ways an antibiotic can kill bacteria. Penicillin, for example, does this by destroying the cell walls of bacteria and preventing their synthesis, killing them.


Bacteriostatics are antibiotics that prevent bacteria from reproducing. Thus, the number of bacteria stops growing, and then they start to die naturally and be killed by the immune system, without overloading it.

Bacteriostatics prevent bacteria from multiplying. They can inhibit cell protein synthesis, which prevents them from dividing. They can even prevent the bacteria’s DNA from duplicating, which stops them from multiplying, leaving the immune system to efficiently eliminate them.

Some deodorants use bacteriostatic chemicals, preventing bacteria that may be present in sweat from multiplying and emitting odors.

Antibiotic classification

There are several varieties of antibiotics that are used for different types of infection.

Antibiotics are separated according to their chemical structures and mechanisms of action. The ratings are as follows:


Used to treat severe infections by aerobic gram-negative bacteria such as Pseudomonas aeruginosa. May cause vestibulocochlear nerve toxicity. Aminoglycoside antibiotics penetrate the bacterium and inhibit its protein synthesis, killing it. One of the representatives is amikacin.


A broad-spectrum antibiotic, it is used for both gram-positive and gram-negative bacteria. It prevents bacterial cell division by inhibiting cell wall production. One of the representatives is meropenem.

Cephalosporins (first to fifth generation)

Cephalosporins are divided into several generations. Each has some differences from the previous one, often in its effectiveness against resistance.

Third-generation cephalosporins, for example, are effective on gram-positive and gram-negative bacteria and are frequently used in nosocomial infections, which are often resistant to several antibiotics due to their place of reproduction.

Fourth-generation ones have the same effect, but are even more effective against gram-positive bacteria and more effective against third-generation resistant bacteria.

Cephalosporins can be represented by cephalexin, from the first generation.


Used in critically ill patients with hypersensitivity to beta-lactam antibiotics such as penicillins and cephalosporins. One glycopeptide is teicoplanin.


Used against respiratory tract infections. Some macrolides can be used against pneumonia. Azithromycin is one of the representatives.


Used against aerobic gram-negative bacteria such as enterobacteria. It is inactive against gram-positive and anaerobic bacteria. Aztreonam represents a monobactam and is the only one available on the market.


Penicillins are used against many types of infections. They were the first antibiotics and have a broad spectrum of action. Amoxicillin is part of this group.

Polypeptide antibiotics

It can be used in cases of eye and urinary infections, specifically those caused by Staphylococcus aureus. Colistin, which belongs to this group, is used to fight hospital infections because, due to its little use, few bacteria have developed resistance to it.


Used in urinary tract infections, bacterial diarrhea, prostatitis caused by bacteria and gonorrhea, among others. Represented by ciprofloxacin.


This type of antibiotic is used against urinary and salmonella infections. Sulfamethoxazole is part of this group.


Chlamydia, syphilis and acne infections can be treated by tetracyclines, among others. Tetracycline is part of this group and is the antibiotic that gives its name.


Used to prevent infections after surgery and to treat acne. Lincomycin is part of this group.

Various antibiotics

Each of these classes has several different antibiotics. They act similarly within their own class, but each class acts differently from the other. Some are more aggressive and cause different side effects or are even capable of causing damage to the body.

There are also antibiotics that do not fit into any of these classifications, such as ethambutol, an antibiotic used to treat tuberculosis and which acts by inhibiting the formation of bacterial cell walls.

The most used

Among the diversity of drugs, each class has the most used antibiotics, according to the indication of the package insert and the physician (a) specialist for each case. Are they:

  • Ciprofloxacin;
  • Amoxicillin;
  • Ampicillin;
  • Azithromycin;
  • Cephalexin;
  • Tetracycline

NEVER self-medicate or stop using a medication without first consulting a doctor. Only he will be able to say which medication, dosage and duration of treatment is the most suitable for your specific case. The information contained on this website is intended to provide information only, and is not intended in any way to replace the advice of a specialist or to serve as a recommendation for any type of treatment. Always follow the instructions on the package insert and, if symptoms persist, seek medical or pharmaceutical advice.

How to know which antibiotic is most suitable?

Only the doctor will be able to indicate which antibiotic is most suitable for you. Contact your doctor if you believe you are dealing with a bacterial infection.

One of the main methods for choosing the antibiotic that will be used in each bacteria is the Gram technique, but a bacterial culture may also be necessary to determine the appropriate drug.

Gram’s technique

Gram’s technique was developed in the late 19th century by Hans Christian Joachim Gram, a Danish physician. The technique involves staining the cell walls of the bacteria with a violet dye and a fixative, lugol.

Both gram-negative and gram-positive bacteria absorb dye and lugol identically and take on a violet color. So 95% ethanol or acetone is used in the bacteria.

In the case of gram-negative bacteria, the walls are dissolved and the stain is eliminated. On the other hand, in gram-positives, the cell walls contract, making them impermeable, and the color is maintained.

Finally, another dye, fuchsin, is used. When looking at the result under a microscope, the gram-positive bacteria will appear violet in color. Gram-negatives will be reddish or pink.

This test is able to indicate whether that specific bacterium has thinner and more sensitive cell walls (gram-negative) or thicker and resistant (gram-positive) in order to decide which type of antibiotic can be used.

Bacterial culture

In addition to Gram’s technique, other tests must be done to identify which bacteria is present and what type of antibiotic is effective on it. Some bacteria may be resistant strains and testing is needed to find the ideal type of drug.

For this, bacterial cultures are performed. A sample of the bacteria is collected and placed in an environment conducive to their reproduction. When there are enough bacteria, you can identify them and run tests with several different antibiotics to find out which ones work and which ones don’t for that particular bacteria.


Bacteria are the smallest type of living thing that exists. Most of them are harmless to humans. Trillions of them live in your body, living harmlessly in you, under the control of your immune system.

However, some of them can be harmful and, until the development of the first antibiotic, infections caused millions of deaths, as the cure depended completely on the patient’s immune system.

In the past, tuberculosis was a death sentence and a cut on the hand could easily lead to the end of a life. Antibiotics have saved millions of people over the years and, along with vaccination, have been hallmarks of modern medicine. It was believed that thanks to them we would eliminate all illnesses caused by bacteria, but that is not exactly what happened.


Bacteria are living beings and, like us, they are subject to adaptations to the environment. Antibiotics make the environment extremely hostile to bacteria, but they are not able to eliminate 100% of them.

Normally, this is not a problem, as the immune system itself tends to take care of the few survivors, but when an antibiotic-resistant bacteria escapes, it can reproduce.

So a new infection can start and this time she will be immune to the antibiotic, as the bacteria from the new infection are descendants of a resistant bacteria.

Currently, antibiotics from the same family as penicillin (today called penicillins) are used, but penicillin itself, discovered by Fleming, hardly appears. This is because most of the world’s pathogenic bacteria have developed penicillin resistance.

Also, some bacteria are able to transfer their immunity to other live bacteria, and some can collect DNA from dead bacteria and absorb their resistance. This can happen even between different species of bacteria, creating a superbug, resistant to several antibiotics.

Super bacteria


Superbacteria are resistant to many antibiotics. They can be created through natural mutations or, more commonly, the misuse of antibiotics.

Antibiotics are prescribed in specific doses and for specific times because these are the doses and time needed for the infection to clear.

Many people stop taking antibiotics when they notice that their symptoms are gone, but that just means that the amount of bacteria present is no longer enough to cause symptoms.

In a 10-day antibiotic treatment, the least resistant bacteria may die on the first day, while the most resistant ones may die on the seventh day. However, if the patient stops taking the antibiotic on the fifth day, the most resistant will remain alive.

They will have been exposed to the antibiotic and may develop resistance to it. After that, they multiply, spreading resistance, and when the disease returns, the same antibiotic will no longer work.

When this type of behavior is repeated too often, the various generations of bacteria, which spread around the world around the infected person, acquire various resistances.

This is especially common in hospitals, where bacteria can be exposed to multiple patients, antibiotics and other bacteria that can transfer their resistance to each other.

Emergency antibiotics

To deal with resistant bacteria, we use several different types of antibiotics, plus some that are controlled for specific use against bacteria resistant to various antibiotics. However, before starting antibiotic therapy, the ideal is to do the antibiogram, to find out what are the resistances of that bacteria.

Side effects

There are many different types of antibiotics and their side effects are varied. The most common ones, however, involve bacteria that are eliminated. Beneficial bacteria that live in the vagina and intestine can be affected by the medication.

Loose stools, diarrhea and nausea are common side effects.


Using antibiotics during pregnancy should be avoided. Some of the strongest ones can cause fetal malformation. The physician must be informed of any infections that affect the pregnant woman in order to be able to indicate the ideal treatment.


There is a possibility that the patient is allergic to the antibiotic. In this case, the treatment must be stopped immediately and it is necessary to see a doctor so that the medication can be changed. It is important that this exchange is made as soon as possible.

The main symptoms of antibiotic allergy are skin rash, shortness of breath and swelling in the mouth and tongue.

Other effects

With the variety of antibiotics, several side effects can arise. Between them:

  • Hearing loss;
  • Vertigo;
  • Kidney injury, stones or failure;
  • Brain damage;
  • Decrease in the number of white blood cells;
  • Light sensitivity (photophobia);
  • Teeth pigmentation;
  • Eye injury;
  • Temporarily low blood pressure;
  • Seizures;
  • Liver damage;
  • Headache;
  • Metallic taste in the mouth;
  • Change in urine color;
  • Diarrhea.
  • Nausea.

Antibiotic makes you fat?

Not! Antibiotics do not make you fat. What happens is that some antibiotics can cause excess gas during treatment, which can give the feeling and appearance of a bloated stomach. This is temporary and once the treatment is completed, the excess gas will also go away.

Drug interactions

Antibiotics are many different drugs and each of them has varied and specific drug interactions. For example, carbamazepine, a drug used to treat epilepsy, has reduced effect during antibiotic use.

It is important to inform the doctor of any medications that are being used during antibiotic treatment so that they can adjust the dose or choose a type of antibiotic that does not interact with your medication.


For a long time there was a fear that antibiotics would reduce the effect of contraceptives. There was a theory that the effect of some antibiotics on gut bacteria reduced the absorption and concentration of the hormone from the pill in a woman’s body. The theory made sense, but studies weren’t done to discover its validity.

However, in recent decades, the problem has been investigated. Studies have shown that an antibiotic is able to reduce the effectiveness of the contraceptive pill: rifampicin, a drug used to treat tuberculosis.

In any case, the ideal is to adopt another barrier method in case of using any type of antibiotic, which is also recommended by some doctors.

How and when to use correctly


Antibiotics were a revolution in modern medicine, but today they are used without the necessary care. There are laws that limit the indiscriminate purchase of antibiotics. For the sale of the drug, it is necessary to present a prescription in two copies, one of which is kept by the pharmacy.

Using the drug correctly helps to prevent the creation of resistance and superbugs, in addition to making the cure of the disease more assured for the patient.

When to use?

The use of antibiotics should be a last resort. If you’re feeling sick, go to the doctor to find out what the disease is and don’t assume it’s a bacteria.

Many diseases are caused by viruses, fungi, protozoa and parasites, and antibiotics do not work against these disease agents. Taking the medicine will only affect the other bacteria in your body, the ones that aren’t causing any problems, and it will build resistance in them.

You should only use antibiotics when the doctor prescribes it, as he has the knowledge of which antibiotic can be used for which bacteria, and he is also the one who knows the dose, times and duration of treatment.

Always respect doses and schedules

Each antibiotic has its specific times and doses to take effect and eliminate bacteria effectively. If you let the drug concentration in the body get too low, the bacteria may have a chance to reproduce again.

However, you should not take more than the dose prescribed by your doctor, as this can lead to unwanted and dangerous side effects.

What if I forget?

If you miss a dose, take the medicine as soon as you can and remember. Keep the spacing between doses.

If you needed to take a dose every 8 hours but missed one and didn’t remember until four hours later, take a dose as soon as you remember and the next dose should be taken 8 hours later.

I got better, now what?

Continue taking the drug until the end of treatment. It is extremely important that you do not stop taking the antibiotic when your symptoms go away. When their numbers drop, the bacteria stop causing symptoms, but many of them are still present.

If you stop the antibiotic, the chances of them reproducing again are high, and worse, they can develop resistance to the drug as only the strongest survived to that point.

Often, the number of doses of an antibiotic treatment matches the number of doses in the medicine box, and reaching the end of the box is necessary.

Drink a lot of water

Drinking water helps the liver to filter the blood more easily, eliminating both dead bacteria and drug remnants. It is recommended to drink around 2 liters of water a day.

Throughout human history, bacteria caused countless deaths until we managed, in the middle of the last century, to develop a game-changing defense. However, the bacteria are still present, evolving and adapting to our best weapon against them, so it is necessary to use antibiotics with care and wisdom.