Simply put, antibiotics are medicines that help us fight bacterial infections inside or on the body.

There are two key ways in which antibiotics work: by killing bacteria (bactericidal) or by preventing the growth of bacteria (bacteriostatic). Some antibiotics do a little bit of both. Some actually kill bacteria but take longer than 24 hours (the accepted criteria for bactericidal antibiotics in medicine) to do it and are therefore called bacteriostatic rather than bactericidal.

Antibiotics can be further divided into broad-spectrum antibiotics (like rifampin) which act against a wide range of bacteria or narrow-spectrum antibiotics which act specifically against a pathogenic bacteria (example, vancomycin which is used to treat infectious colitis or gut inflammation).

Antibiotics can be synthetic or they can be derived from natural sources like fungi. Indeed, the original penicillin (the first antibiotic in the world) was made from mould fungus. Synthetic drugs are made in a lab, without using any natural ingredients. Examples of synthetic antimicrobial agents that are effective against bacteria include sulphonamides, cotrimoxazole, quinolones.

In 1945, the person who discovered penicillin, Alexander Fleming, also foretold a future where people would use antibiotics indiscriminately and give rise to antibiotic-resistant bacteria. In his Nobel Prize lecture, Fleming said: “The time may come when penicillin can be bought by anyone in the shops. Then there is the danger that the ignorant man may easily underdose himself and by exposing his microbes to non-lethal quantities of the drug make them resistant.”

The world over, antibiotic resistance has indeed become a big problem today. To counter this problem, scientists are looking at new ways and drugs to fight bacteria. Medical practitioners have also become more judicious about using the latest diagnostic techniques to prescribe the right medicines for the right microbe (narrow spectrum)—thereby, reducing the chances of drug-resistance.

You, too, can do your part:

  • Complete the course of medicine your doctor prescribes, even if you feel better before the course is finished.
  • Go for a checkup after completing the medicine or therapy course, to know if you should continue or discontinue the medicine. 
  • Do not to self-medicate. Even if you get the same symptoms a second or third time, do not use an old prescription. Make sure you see the doctor again, for a proper diagnosis. 

Unless all stakeholders—people like us, doctors, scientists, pharma companies—work together, there may come a time when antibiotics are no longer as effective against harmful bacteria. Scientists and doctors fear that when such a time comes, the gains achieved by antibiotics—such as increased life span—may be reversed.

Read on to know more about antibiotics: their types, uses, how do they work, side-effects and the problem of resistance.    

  1. What are antibiotics and how do they work?
  2. Types of antibiotics
  3. Uses of antibiotics
  4. Benefits of antibiotics
  5. Side effects of antibiotics
  6. Takeaways for using antibiotics
Doctors for What are antibiotics?

Antibiotics are drugs that fight pathogenic bacteria, or bacteria that cause infection. Before the discovery of antibiotics, medical history shows that sexually transmitted diseases like syphilis were incurable, three out of 10 pneumonia patients died, nine in 1,000 women died in childbirth, ear infections led to hearing loss and Strep throat could lead to heart disease. Many of these ailments are preventable or treatable today, thanks to antibiotics.

Though we use the term as a catch-all there are four distinct ways in which antibiotics fight bacteria:

  • By disrupting bacterial cell wall synthesis: All bacteria have an outer membrane (cell wall) made with peptidoglycans—a compound of sugars and amino acids that is then arranged and cross-linked in a particular way to strengthen the wall. Antibiotics like beta-lactams interfere with the way some bacteria make this wall, resulting in weaker bacteria walls. When the bacterial walls are weak, our immune system is able to beat the infection. Beta-lactams are used to treat problems like strep throat and staphylococcus infections.
  • By stopping DNA replication in bacteria: Bacteria use an enzyme called DNA gyrase to multiply. Antibiotics such as fluoroquinolones target this enzyme, to stop the bacteria from making copies of itself. When the harmful bacteria is unable to make copies of itself and spread, the infection dies out.
  • By inhibiting protein synthesis in bacteria: While humans also synthesize proteins in the body using ribosomes, bacterial ribosomes are different from human ribosomes in structure and function. There are two ways in which this type of antibiotics work:
    • By blocking RNA transcription: In order to make copies of itself, bacterial DNA makes RNA. This RNA then tells the bacterial cells how to make specific proteins to perform various functions that are essential for the bacteria's survival and growth. But if the DNA to RNA transcription is halted, the entire process gets stalled. In the absence of proteins, bacterial cells can't function properly and they die out. Rifampin is an example of an antibiotic that works like this.
    • By blocking bacterial ribosomes: Ribosomes synthesise the proteins, based on the directions they get from bacterial RNA. Antibiotics can bind with one of the two subunits (large or smaller) of ribosomes to interfere with protein synthesis. Streptomycin, erythromycin, doxycycline, all work like this.
  • By blocking specific bacterial metabolism: Unlike humans, bacteria make their own vitamin B9 (folate) which is essential for DNA synthesis. Antibiotics that block any of the steps by which bacteria make vitamin B9 stall DNA synthesis too. A combination of sulfonamides and trimethoprim is an example of this type of antibiotic.

Read more: Precautions to take while using antibiotics

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Antibiotics are often hailed as one of the biggest achievements of modern medicine. Indeed, before the COVID-19 pandemic struck in late 2019, non-communicable diseases had overtaken infectious diseases as the cause of death in many countries.

Even as drug resistance rears its ugly head, antibiotics continue to be life-saving in many situations. As mentioned above, antibiotics work in one of two ways:

  • By killing bacteria: bactericidal
  • Or by inhibiting the growth of bacteria in the body: bacteriostatic

Among the antibiotics that work by stopping further growth of bacteria are:

  • Glycylcyclines: They work by preventing protein synthesis thereby inhibiting further growth of the bacteria. These medicines are effective against some drug-resistant bacteria like methicillin-resistant Staphylococcus aureus or MRSA which can cause skin infections and bacterial pneumonia. If left untreated, MRSA can cause sepsis or toxic shock syndrome also.
    Examples of glycylcyclines include tigecycline, which is sometimes used to treat hospital-acquired pneumonia caused by multi-drug resistant Acinetobacter baumannii (MDRAB).
  • Tetracyclines: Discovered by Benjamin M. Duggar in 1948, these broad-spectrum antibiotics are even effective against protozoan parasites—tetracyclines like doxycycline are still used today to treat and prevent malaria. Tetracyclines, previously known as chlortetracycline, are used in the treatment of urinary tract infections (UTIs), chlamydia (a sexually transmitted disease) and various conditions of the skin (for example, severe acne) and eyes. Unfortunately, tetracyclines are also used as growth promoters in the poultry and meat industry—this has made some bacteria resistant to tetracyclines.
  • Lincosamides: These medicines are mostly used in cases of infection by staphylococcus, streptococcus, Bacteroides fragilis and C. difficile bacteria (especially Clostridium difficile colitis or gut inflammation due to C. difficile). They are also used to treat toxic shock syndrome. Lincosamides like clindamycin are particularly useful for the treatment of patients who are allergic to penicillin.
  • Macrolides: Azithromycin, clarithromycin, erythromycin are all types of macrolides which are derived from a soil-borne bacterium known as Saccharopolyspora erythraea. These broad-spectrum antibiotics are used in the treatment of illnesses from pelvic inflammatory disease (PID) to acute exacerbations of COPD (chronic obstructive pulmonary disease that becomes worse suddenly). An interesting fact: though antibiotics are not usually used for viral infections, azithromycin was being tested in combination with pneumonia drug atovaquone for the treatment of COVID-19.
  • Oxazolidinones: A relatively new group of antibiotics, these synthetic drugs are effective against several bacteria that are resistant to methicillin, vancomycin and even penicillin. Examples include linezolid which is used in the treatment of pneumonia and some skin infections.
  • Sulpha drugs or sulphonamides: UTIs, bronchitis, eye infections, bacterial meningitis (inflammation in the meninges or the tissue that covers the brain and spinal cord) and traveller's diarrhoea are among the conditions that are treated with sulpha drugs.

Medicines that kill bacteria include:

  • Aminoglycosides: Used in chemotherapy till the 1980s, today these semi-synthetic antibiotics are used to treat respiratory tract infections, tuberculosis (especially in patients who have been treated for TB before) and chronic Pseudomonas aeruginosa lung infection (which can be hard to treat) in cystic fibrosis. Researchers say this class of antibiotics also works well with others and may be useful to overcome some types of antibiotic resistance. Some examples include streptomycin (in clinical use since 1944) and arbekacin.
  • Beta-lactams: This class of antibiotic drugs includes penicillin and its derivatives, cephalosporins and carbapenems. Perhaps the most popular example, after penicillin, is Amoxicillin. These medicines are used for the treatment of a wide range of diseases like:
  • Fluoroquinolones: Often used in the treatment of urogenital disorders like bacterial prostatitis and UTIs, bone infections like osteomyelitis and respiratory infections. Examples of fluoroquinolones include ciprofloxacin, levofloxacin and moxifloxacin. These medicines are also used against some drug-resistant infections.
  • Glycopeptides: These medicines work by preventing the cell wall formation in bacteria. The most well-known glycopeptide is vancomycin which is used to treat colon infections.
  • Cyclic lipopeptides: These relatively new antibiotics are made with naturally occurring substances. These medicines are used as a last resort, against drug-resistant bacteria. Example: Daptomycin, which is used for the treatment multidrug-resistant S. aureusStreptococcus pyogenesStreptococcus agalactiae and Enterococcus faecalis.
  • Nitroimidazoles: The most famous example of this type of antibiotic is metronidazole, the first drug that was effective against Trichomonas vaginalis (a protozoa) which causes trichomoniasis, a common vaginal infection.

Antibiotics are widely used today to prevent and treat a range of bacterial (and protozoan) infections such as:

To be sure, these are just some of the bacterial diseases that can be treated or managed with antibiotics today.

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Microbiome comprises thousands of bacteria that live on and inside our bodies without harming us. However, some of these bacteria can cause infection if they get the opportunity—for example, in immunocompromised people. Pathogenic bacteria are those bacteria that cause infection and disease—they don't coexist with us. Antibiotics may be used for the prevention or treatment of both.

Infection occurs when the bacteria becomes strong enough to overcome the body's immune system. Unless treated, infections can worsen and cause complications.

Depending on the types of antibiotics used, they may have benefits such as:

  • Antibiotics act quickly, to provide relief from infections and their symptoms and complications.
  • Broad-spectrum antibiotics can help in emergency situations when there is no time to run tests and identify the specific pathogen.
  • Antibiotics for drug-resistant bacteria help in the treatment of health conditions like multi-drug resistant tuberculosis.
  • Antibiotics can be taken orally or used topically, depending on the health condition.
  • Because antibiotics work in four different ways, there is a lot that doctors can do to fight most bacterial disease today.
  • People allergic to one class of antibiotics may be put on another, given how many types of antibiotics there are today.
  • In use since the 1940s, antibiotics are to be credited for the increase in expected lifespan.
  • Most antibiotics can be used for patients of different ages and stages in life.

All medicines have some side-effects. Your doctor weighs these against the damage that the infection can do, before prescribing the medicines to you.

That said, the side effects of antibiotics can vary depending on the specific salts. Here are some of the most common side effects:

  • Headaches
  • Nausea and vomiting
  • Skin rashes
  • Diarrhoea
  • Antibiotics can kill good bacteria as well as bad bacteria in the body. This can disturb the natural microbiome in your body and lead to other infections
  • Drug-induced liver injury is a real risk with antibiotics, as these are processed in the liver
  • Some antibiotics like aminoglycosides can affect the kidneys. Some, like sulfonamides, can increase your risk of kidney stones.

Antibiotics are usually contraindicated (not advised) during pregnancy and breastfeeding. This is because most antibiotics can reach the baby through the placenta or breast milk, as the case may be. That said, there are some conditions in which a doctor may recommend antibiotics even to expecting and lactating moms. For example, pregnant women who test positive for syphilis are given treatment during pregnancy to prevent problems like miscarriage and stillbirth.

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In ancient Egypt and Syria, healers used mouldy bread to treat open wounds. By the mid-1800s, germ theory became widely accepted. By the early 1900s, scientific thinkers started looking at disease-causing microbes more closely to find a cure. In the 1920s, Alexander Fleming investigated an accidental mouldy growth in his lab and discovered penicillin—it would still be a few years before it could be stabilised and commercially produced. But penicillin changed modern medicine.

Hardly anyone would remember a time before 1928 when modern antibiotics were first discovered. However, medical literature shows that bacterial infections like tuberculosis and pneumonia and open wounds that got infected by bacteria were major causes of death back then. Today, we think of these as largely treatable, thanks to antibiotics.

This is not to say that bacterial infections have stopped being a threat to humans. Indeed, each year tuberculosis still claims tens of thousands of lives in India. Many of these people develop drug-resistant forms of TB in which many antibiotics no longer work. And sepsis still kills more people each year than cancer. These are just two examples out of hundreds where antibiotics improve quality of life, and in many cases, save lives.

Going forward, it is important that each of us is more mindful about the antibiotics we use and the way we use them. As researchers simultaneously develop better antibiotics and newer therapies to treat bacterial infections, even those infections that are caused by drug-resistant bacteria.

Dr Rahul Gam

Dr Rahul Gam

Infectious Disease
8 Years of Experience

Dr. Arun R

Dr. Arun R

Infectious Disease
5 Years of Experience

Dr. Neha Gupta

Dr. Neha Gupta

Infectious Disease
16 Years of Experience

Dr. Anupama Kumar

Dr. Anupama Kumar

Infectious Disease


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