In this blog post, we will explain in simple terms the causes of antibiotic resistance in bacteria, how it works, and how it spreads.

Understanding the causes and mechanisms of antibiotic resistance in bacteria

Antibiotics are one of the most important weapons in modern medicine for treating bacterial infections. However, in recent years, there have been increasing cases where antibiotics are no longer as effective as they used to be. The reason for this is “antibiotic resistance.” In this article, we will take a scientific look at how bacteria become resistant to antibiotics and how this resistance spreads.

Genetic Information and Protein Synthesis: The Basic Life Processes of Bacteria

Bacteria store most of their genetic information in DNA stored in chromosomes. This DNA contains the information necessary to synthesize proteins, which are essential for life within cells. Proteins are key components that perform cellular functions and are synthesized in organelles called ribosomes after receiving information from DNA. Ribosomes are the only organelles in cells that produce proteins, making them indispensable for life.
Proteins that are essential for life are produced in a constant amount, but in response to environmental changes or crisis situations, certain proteins are synthesized rapidly in large quantities. This is an important physiological feature that allows bacteria to adapt quickly to their environment.

The emergence and mechanism of antibiotics

Antibiotics, or antimicrobial substances, were discovered in fungi and soil bacteria in nature, and their development began in earnest. Antibiotics work by binding to various enzymes in the cell membrane, cell wall, or inside the cells of bacteria. This inhibits the activity of enzymes necessary for DNA replication and protein synthesis, thereby preventing the growth of bacteria or inducing their death.
However, as antibiotics became widely used, problems began to emerge. Some bacteria developed resistance to antibiotics, enabling them to evade their effects. This is mainly caused by excessive use and misuse of antibiotics. As a result, resistant bacteria have become selectively preserved, and their proportion has increased significantly over time.

Antibiotic resistance in bacteria: Various manifestations

Antibiotic resistance is not simple. Bacteria can acquire or express resistance in various ways. The following are some of the most common methods.

Blocking antibiotic absorption

Bacteria have the ability to absorb foreign substances through their cell membranes and excrete unnecessary substances. Antibiotics enter the bacteria through specific transport systems in the cell membrane and take effect. However, some resistant bacteria partially interfere with the function of these transport systems, preventing antibiotics from easily penetrating the cells. This allows the bacteria to maintain a certain level of survivability against antibiotics. However, this defense can be easily neutralized by high doses of antibiotics.

Antibiotic efflux

Other resistant bacteria use energy to quickly expel antibiotics that have entered their cells. These bacteria can survive even at high concentrations of antibiotics, giving them much stronger resistance.

Antibiotic degradation or modification

Some bacteria produce enzymes that chemically break down or modify antibiotics. These enzymes act selectively on specific antibiotics, rendering them ineffective. Interestingly, this resistance can be neutralized by “decoy substances.” Decoy substances have a similar structure to antibiotics, so while resistant bacteria attack the decoy substances instead of the actual antibiotics, the real antibiotics are able to act unhindered.

Changes in target structures

Another method is to change the target structure within the bacteria that the antibiotic binds to. For example, if an antibiotic acts on a specific enzyme or part of a ribosome, even a slight change in the structure of that area will prevent the antibiotic from binding. In this case, the bacteria can avoid binding to the antibiotic while maintaining their original function, allowing them to continue their life activities.

Mass production of similar proteins

Instead of directly altering the target enzyme, some bacteria produce large amounts of similar proteins to induce the antibiotic to bind to them. This protects the important enzyme and renders the antibiotic ineffective.

Spread of resistance genes: exchange between bacteria via plasmids

In addition to chromosomes, bacteria also have small ring-shaped DNA called plasmids. These plasmids contain additional genetic information, such as resistance genes, and can be transferred between bacteria. This is one of the main reasons why antibiotic resistance spreads so quickly.
For example, suppose there are bacteria B1 that is resistant to penicillin and bacteria B2 that is resistant to cephalosporin. B1 replicates the plasmid containing the resistance gene and forms a cilium structure called “flagella” to transfer this plasmid to other bacteria. Once the flagella are complete, B1 and B2 form a junction, and the replicated plasmid moves to B2.
During this process, B2 acquires plasmids containing two types of resistance genes. Furthermore, the two plasmids may combine into one. At this point, a specific piece of DNA from one plasmid is separated and connected to an open section of the other plasmid, forming a composite plasmid that is resistant to both antibiotics. The resulting plasmid can be replicated again and transferred to other bacteria.

Environmental factors contributing to the spread of antibiotic resistance

Antibiotic resistance does not arise solely from the evolution of bacteria. Environmental factors also play an important role in its spread. Some antibiotics remain active in the environment until they are broken down. These residual drugs selectively promote the survival of resistant bacteria, thereby increasing the proportion of resistant bacteria.
In particular, in environments where antibiotics are frequently used—such as hospitals, laboratories, livestock farms, and contaminated sewage—plasmid exchange between bacteria occurs more actively, and the speed at which resistance genes spread increases accordingly. If such conditions persist, the likelihood of complex bacteria that are resistant to multiple antibiotics at the same time will eventually increase.

Conclusion: Antibiotic resistance, a challenge that humanity must face together

Antibiotic resistance is not simply a medical problem. It is a complex social issue linked to the environment, food, and industry as a whole. There is an urgent need for the careful use of antibiotics, appropriate management and policies to prevent the spread of resistance, and improved public awareness.
We are no longer in an era where antibiotics are a panacea. If we do not make the right choices now, treatable infectious diseases could once again become a deadly threat. Based on a scientific understanding of antibiotic resistance, it is time to work together to create a sustainable system for responding to infectious diseases.