How Do Bacteria Become Resistant To Antibiotics?

After Dr. Alexander Fleming returned from his holidays, he found mold growing in cultures of a bacteria species. He found that the mold was capable of stopping any further growth of the bacteria. Thus began an era of a novel group of medicines called antibiotics. Antibiotics have been used to kill germs and treat diseases for over a century.

Antibiotics are so good at killing germs that many people resort to overusing them or using them when they are not the appropriate treatment. Such increased use of antibiotics has helped bacteria and fungi to adapt to the effects of these drugs. When germs are not killed by the same antibiotics anymore, these germs are said to be antibiotic resistant and are currently a major medical hurdle.

Penicillium notatum
Penicillium notatum, Credit: Wikimedia/Louis Bontemps

Table of Contents

How do antibiotics work?

To understand how bacteria grow resistant to antibiotics, we need to know how these drugs act. Antibiotics either kill the germ or stop its growth without killing it. Antibiotics attain these objectives in three major ways:

• Most bacteria have an outer covering called a cell wall. This is like a jacket that protects the bacteria from the environment. Antibiotics attack and disrupt the cell wall. A cell mostly contains liquid matter. How do you store water? In a container, right? The cell has a similar elastic container to keep the cell contents inside. This is the cell membrane. These are sweet spots for antibiotics to act on. These drugs disrupt cell walls and cell membranes and block processes that form membranes and cell walls.

Diagram of a gram-negative cell wall.
Diagram of a gram-negative cell wall, Credit: Wikimedia/Jeff Dahl

• Bacteria need to make DNA and RNA regularly to survive. Antibiotics target the cell’s ability to produce DNA and RNA, killing the germs.

• Proteins run almost the entire show inside cells. Proteins act as signals, receptors, and enzymes, and also help in absorbing nutrients. Antibiotics target parts of cells that make proteins. Without these proteins, the bacteria and fungi die.

You may think, how do antibiotics severely damage germs but leave our cells alone? This is because human cells and the pathogens that attack our bodies are different. Antibiotics are picky about whom they target. So much so, that these drugs do not even affect the viruses that cause flu and colds.

What causes antibiotic resistance?

Abuse of antibiotics is at the root of antibiotic resistance. When antibiotics are consumed, some of the germs die. However, some pathogens bypass the effects of these drugs and multiply. This is a natural process in bacteria and fungi. The resistant strains can then be spread due to a lack of hygiene. Lack of hygiene is always associated with the spread of contagious diseases, and it is no different for germs immune to these drugs.

How antibiotic resistance happens?:

Bacteria develop defense tactics against antibiotics over time. Proteins and nucleic acid control most of the actions and events in a cell. The pathogens produce specific proteins which decide how the germ will fend off the antibiotic. In some cases, certain bacteria or fungi can become fully immune to all of these drugs. Let us see some ways by which bacteria grow resistant to antibiotics:

Restricting entry of antibiotics: Bacteria have channels in their membrane. These channels are like tunnels through which substances can enter and come out. Antibiotics move into cells through these channels. Bacteria change the shape and structure of the channels to prevent antibiotics from entering. In other cases, bacteria close off many of these channels. Some bacteria develop thicker cell walls.

Changing the target sites: As mentioned, antibiotics are picky about what they target. Although this makes them perfect for attacking certain bacteria, this is also a boon for germs. What if the germs evolve to change these target sites? For example, penicillin binds to certain proteins in the cell walls of bacteria. Bacteria change the structure of these proteins, leaving penicillin with fewer sites to bind. Genes are like the blueprint of how bacteria will function and act. Products of genes also induce changes in cell walls and membranes. This changes how the target site appears to the drug.

Some antibiotics target metabolic pathways. Let us picture the substances that bacteria absorb as raw materials. What is done to raw materials in a factory? They are passed through various devices to yield a final, usable product. In cells, these raw stuffs are processed through chemicals called enzymes, to yield matter that the germ will use. Some antibiotics shut down these cell systems. If germs change the shape of certain enzymes, antibiotics can fail to spot these enzymes. This nullifies the effects of the drug.

Destroying the drug: Some bacteria simply destroy the drug and render it inactive. They make various enzymes for this process. These enzymes are made based on signals from genes.

Getting rid of antibiotics: Have you heard about how doctors treat patients who have been poisoned? The first thing they try is to get the poison out of the patient’s body. Similarly, germs throw out antibiotics, which are like poison to the germ. They do so with special parts called efflux pumps. This technique prevents these drugs from doing any harm to the germs, and they survive and grow.

Antibiotic resistance mechanisms
Antibiotic resistance mechanisms, Credit: Wikimedia/Gerard D Wright

How to stop antibiotic resistance?

Antibiotic resistance is a global issue. Efforts from doctors and the public are needed to stop this issue from growing bigger. Doctors should prescribe antibiotics only if needed. You should never take antibiotics without asking your doctor first. These drugs are not to be shared. Do not advise any other person to take these drugs without a doctor’s oversight.

Popping a pill is not always the best option, and can actually do more harm than good. Multiple health associations have come forward to warn people about antibiotic abuse and antibiotic resistance. With some effort from the people, we can beat this global issue.


Cultures: Cultures are a way to grow microorganisms inside glass equipment (in vivo).

Receptor: A substance to which a molecule binds; in response, the substance signals for some effect in the cell.

Enzymes: Substances that make a biochemical reaction proceed faster than it would in the normal environment.

Strain: A strain is a subtype of a microorganism, which has different characteristics than other types.

Genes: The part of a cell that passes characters of a cell to its offspring

Efflux pumps: These remove toxic substances from the bacterial cell.

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How do antibiotics work?