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How Antibiotics Work

Antibiotics work according to the mechanism of action (what the drug “targets” in microbes or how the drug “works” in the microbe) that is driven by the drug’s distinguishing chemical structure.

Chemical structures also define the “classification” of antibiotics. If you hear doctors talk about “macrolides” versus “quinolones”, they are talking about families of drugs (not “one” specific drug) and they are referring to the way each family of drugs targets microbes.

When you hear about “generations” of an antibiotic, this means the chemical structure of the current drug has been modified (changed) somehow. These changes are designed to improve the action of the drug, especially when the bacteria have evolved to resist the original drug.

A well known example is Penicillin resistance. Overuse of penicillin resulted in widespread bacterial resistance to this drug. If I went to the doctor today and the doctor decided that a beta-lactam based antibiotic was appropriate, the doctor may prescribe amoxicillin or one of the newer generation cephalosporins versus the original penicillin. That’s because the doctor is thinking the bacteria in my body will probably laugh at penicillin and a “newer” penicillin (like amoxicillin) may be needed.

Why We must complete the ENTIRE course of antibiotic therapy

One of the biggest problems in antibiotic resistance, besides antibiotics being over-prescribed, is patients stopping their medication as soon as they start feeling better instead of finishing their entire course (taking ALL pills prescribed by the doctor).

Imagine your body is a kingdom and your immune system as a fortress/defense system. Your kingdom has undergone an invasion. Taking antibiotics is similar to giving your immune system a much needed weapon to defeat the invaders.

A full course of antibiotic therapy aims to kill off as many invaders that have infiltrated your kingdom within as short amount of time as possible, so that your defense system can take care of the rest, and to ensure that ALL the invaders are killed.

People sometimes stop taking the antibiotic when they start feeling better (“Oh, I’m already feeling better”) or for another reason (“hey, maybe I should save these couple of pills, just in case, for next time”). The problem is that there may be a few invaders that have thus far evaded the antibiotic response, and these will be the invaders who will come back with a vengeance, literally.

Your feeling better has do to with most of the invaders being killed off, but the few that have escaped being killed are buying time to adapt and evolve… to become smarter against your defenses.

Antibiotic resistance arises from the ones that have been allowed to escape because the host (you) decided “All is well, call off the troops!” and giving the invaders time to learn how to better take you down the next time there is an opportunity.

Based on the way each antibiotic family targets microbes, the drugs in that antibiotic family may either kill (bactericidal) or stall the growth of (bacteriostatic) microbes.

This is where we get into the specifics of “how” an antibiotic works. Antibiotics aim to kill by:

  • Targeting a specific feature of bacteria
  • Targeting the reproductive process of bacteria
  • Targeting a critical chemical pathway in bacteria (especially protein synthesis)
  • Overcoming bacteria’s evolved mechanisms of resistance (for example, bacteria that have evolved pumps in their membranes to “pump out” drugs)

Targeting a Specific Feature of Bacteria, Reproduction, or critical process (typically making proteins or “protein synthesis)

Antibiotics that target gram positive bacteria will disrupt the chemical process critical to making the thick peptidoglycan wall (the thick wall is what holds the “gram stain” that allows us to visually identify the “gram positive” bacterial strain).

However, if the bacteria has a thin peptidoglycan wall (this then won’t show up as bright violet stains on the gram stain, making this bacteria a “gram negative” type), then an antibiotic that targets that wall won’t do much damage.

Instead, you’d need an antibiotic that targets a specific feature of gram negative bacteria or target a critical process like protein synthesis. For example, the antibiotic can cross the gram negative bacteria’s cell wall (but are blocked by gram positive bacteria’s peptidoglycan layer) to stop protein synthesis, which stops many critical machinery in bacteria.

Antibiotics that target the bacterial reproduction prevents new bacteria from being produced. This gives your body a fighting chance to go over the existing microbes.

Updated: June 22, 2016 — 12:01 pm

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