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  • Writer's pictureMed Insider

Overview of Antibiotic Resistance

By Nicole Blattman


  • Antibiotics have existed for over a century.

  • Antibiotic resistance occurs when the very bacteria an antibiotic is designed to kill is able to overpower the drug itself and continue to grow.

  • Resistant bacteria occur due to random mutation and spread of resistance genes. Bacteria do not adapt to antibiotics.

  • Resistance genes can come in the form of 5 main resistance mechanisms.


Over a century ago, German scientist Paul Ehrlich discovered arsphenamine, a substance able to selectively kill bacteria that cause syphilis. Ehrlich’s discovery incited a future of antibiotic development that changed the face of medicine. Just a few years later, Alexander Fleming discovered penicillin, which was soon widely distributed across the globe. Ever since this mass production of antibiotics began, a similar mass spread of antibiotic resistance has followed. Antibiotic resistance occurs when the very bacteria an antibiotic is designed to kill is able to overpower the drug itself and continue to grow. Today, antibiotic resistance is a substantial global health threat, associated with millions of deaths each year.

How Does Antibiotic Resistance Work?

A common misconception of antibiotic resistance is that bacteria are able to adapt in order to resist antibiotics. This is not the case. Rather, killing susceptible bacteria allows bacteria that have acquired random mutations that cause resistance to survive and reproduce, spreading their resistance genes to their offspring. Sometimes, resistance genes can even be spread “horizontally,” or to their neighboring bacteria rather than their offspring.

Resistance Mechanisms

Resistance genes or mutations can come in the form of different resistance mechanisms. There are 5 main types of resistance mechanisms:

  • Limiting drug uptake

    • This occurs when bacteria, gram negative bacteria specifically, have a thick outer layer known as the LPS, or the lipopolysaccharide layer. This layer acts as a barrier to certain antibacterial agents. Some antibiotics can enter gram negative bacteria through channels known as porins. Certain resistance genes may decrease the number of porins, for example.

  • Modification of drug targets

    • Antibiotics target certain proteins that can bind to them. Resistance genes could impact the number of these proteins or the structure of these proteins, making them less able to bind to antibiotics.

  • Drug inactivation

    • Resistance genes may allow bacteria to degrade the antibiotic itself, or possibly inactivate the drug by transferring a chemical group of the antibiotic.

  • β-lactamases

    • β-lactam drugs are the most widely used antibiotics. Resistance to these drugs can occur by preventing the ability of their binding proteins to attach to the antibiotic, by acquiring efflux pumps which pump out antibiotics from the bacteria, or by breaking down the antibiotic using specific enzymes.

  • Drug efflux

    • Efflux pumps can rid the bacteria of antibiotics in a more general fashion. These pumps are not always specific to a certain antibiotic, but can cause resistance to many drugs at once.


Infections caused by antibiotic-resistant bacteria can be extremely difficult or impossible to treat. These infections could be deadly or require extensive care. The best way to prevent antibiotic resistance is to prevent disease: practice good hygiene, wash your hands, take care of any wounds or conditions, and get any recommended vaccinations.

If you do get sick, make sure to consult with your healthcare provider about whether antibiotics are necessary. Viral infections cannot be cured by antibiotics, and taking these drugs can lead to antibiotic resistance. They should only be taken if needed.



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