What Are the Applications of an Antibiogram?

The antibiogram is a method that determines the most appropriate antibiotics for the treatment of bacterial infections. Today's article will tell you more about its uses, so read on.
What Are the Applications of an Antibiogram?

Last update: 28 September, 2021

An antibiogram provides information to a physician so they know just which drug to prescribe. This is because the various types of bacteria don’t respond equally to the same antibiotics. Likewise, drugs are different and only attack a certain type of infectious agent.

OK, but why is it that not all microorganisms fall to the same antibiotic? This is a common question and the answer is in the concept of evolution. This is because microorganisms evolved to have mechanisms to evade substances that keep them from surviving.

We must know these resistances in advance in order to be able to apply the appropriate treatment to the infected person. For this purpose, the antibiogram reveals the sensitivity of a given bacterium to certain antibiotics.

Resistance to antimicrobials

Bacteria become resistant over time, based on their need to survive. Drug resistance, which we can observe in antibiograms, has two categories:

  • Innate mechanisms that a family of bacteria has naturally written into its genetic code (they already had it way before the application of antibiotics)
  • Acquired mechanisms as certain bacteria created methods to resist or fight antibiotics (they went from being sensitive to these drugs to being resistant)
A lab technician at work.
An antibiogram reveals bacterial resistance, both innate and acquired.

An example of acquired resistance

An example of acquired resistance is what happened after the discovery of penicillin by Alexander Fleming. Penicillin was the main antimicrobial in the 1940s but a bacterium called Staphylococcus aureus soon developed resistance.

Penicillin is an antibiotic that binds to an enzyme generated by the bacterial wall. In other words, this substance inhibits the synthesis of the bacterial wall, leaving the microorganism unprotected and leading to its death. However, Staphylococcus aureus generated enzymes called penicillinases to break down the penicillin molecule.

Dangers of antimicrobial resistance

The Centers for Disease Control and Prevention (CDC) wrote a 2019 report on the threat of antibiotic resistance in the USA, showing that the number of resistances remains high. Currently, there are 2.8 million antibiotic-resistant infections.

Looking at all this data, the threat posed by antibiotic resistance is worrying and frightening. According to the World Health Organization (WHO), the use and abuse of antimicrobials increased the number and types of resistant microorganisms in recent years.

What’s an antibiogram?

This is a test that helps us to determine the most appropriate antibiotic to specifically treat the infecting bacteria. A physician extracts a sample from the focus of the infection to isolate the causative microorganism when a person has an infection.

Then, the microorganism grows in a controlled medium, a culture, to determine what type of bacteria it is and to which family it belongs. Once this step is done, lab technicians grow it in another medium with antibiotic-releasing tablets.

The bacteria grow in this new culture but those sensitive to antibiotics leave a halo around the tablet. This halo indicates that the bacteria wasn’t able to reproduce because the antibiotic prevented it.

A person holding five capsule blisters
The indiscriminate use of antibiotics has increased the resistance of bacteria. Thus, the antibiogram is now more valuable than it was decades ago.

Treatment according to an antibiogram

A very serious infection leaves no time to wait for the results of an antibiogram. Based on the patient’s characteristics, the focus of the infection, and whether the infection was contracted outside or inside the hospital, the patient is treated with broad-spectrum antibiotics.

These broad-spectrum drugs cannot be deliberately applied to everyone who has an infection. This is because their indication implies the risk of resistance. Of course, there’s no problem if they become resistant as we wouldn’t be able to apply the same antibiotic in severe infections.

On the other hand, targeted treatment is that which is tailored to the bacteria in question. It’s determined by the antibiogram, which indicates the antibiotic to use.

Avoiding bacterial resistance

Preventing bacterial resistance is necessary and vital for humanity. Furthermore, therapeutics will be ineffective and the consequences serious if microorganisms become too resistant.

The number one advice is to take the right dose of the prescribed antibiotic as per the doctor’s instructions. You can’t stop taking the medication even if you feel better, nor can you modify the amount according to your personal taste.

The use of an antibiogram will be the norm if you come across a resistant bacterium, in spite of any precautions you may take. It’s a powerful biochemical tool to treat serious infectious cases.

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