3.1 Definition of resistance

Activity 12: A recap on definitions

Recall the definitions of:

  • antimicrobial
  • antibiotic
  • antibacterial.

Discussion

The definitions are as follows:

TermDefinition
AntibacterialCompounds that kill or inhibit the growth of bacteria.
AntibioticCompounds that kill or inhibit the growth of microbes/micro-organisms. ‘An antibiotic is an agent or substance that is produced by or derived from a micro-organism that kills or inhibits the growth of another living micro-organism. Antibiotic substances that are synthetic, semi-synthetic, or derived from plants or animals are, strictly speaking, not antibiotics. However, for the purposes of this module they are included. In this document “antibiotic” refers to an antimicrobial agent with the ability to kill or inhibit bacterial growth.’ (WHO, 2019)
AntimicrobialCompounds that kill or inhibit the growth of microbes/micro-organisms. ‘An antimicrobial is an agent or substance derived from any source (micro-organisms, plants, animals, synthetic or semi-synthetic) that acts against any type of micro-organism, such as bacteria (antibacterial), mycobacteria (anti-mycobacterial), fungi (antifungal), parasite (anti-parasitic) and viruses (antiviral).’ (WHO, 2019)

Activity 13: Understanding resistance

Watch the following video on antibiotic resistance, up to 2:38. Don’t worry if you hear some terms in this video that you are unfamiliar with; it is important that you understand the overall concept of resistance to antibiotics in bacteria.

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Transcript: Video 6

[MUSIC PLAYING]

NARRATOR:
What if I told you there were trillions of tiny bacteria all around you? It's true. micro-organisms called bacteria were some of the first life forms to appear on Earth. Though they consist of only a single cell, their total biomass is greater than that of all plants and animals combined. And they live virtually everywhere, on the ground, in the water, on your kitchen table, on your skin, even inside you.
Don't reach for the panic button just yet. Although you have 10 times more bacterial cells inside you than your body has human cells, many of these bacteria are harmless or even beneficial, helping digestion and immunity. But there are a few bad apples that can cause harmful infections, from minor inconveniences to deadly epidemics.
Fortunately, there are amazing medicines designed to fight bacterial infections. Synthesised from chemicals or occurring naturally in things like mould, these antibiotics kill or neutralise bacteria by interrupting cell wall synthesis, or interfering with vital processes, like protein synthesis, all while leaving human cells unharmed.
The deployment of antibiotics over the course of the 20th century has rendered many previously dangerous diseases easily treatable. But today, more and more of our antibiotics are becoming less effective. Did something go wrong to make them stop working? The problem is not with the antibiotics, but the bacteria they were made to fight. And the reason lies in Darwin's theory of natural selection.
Just like any other organisms, individual bacteria can undergo random mutations. Many of these mutations are harmful or useless. But every now and then, one comes along that gives its organism an edge in survival. And for a bacterium, a mutation making it resistant to a certain antibiotic gives quite the edge.
As the non-resistant bacteria are killed off, which happens especially quickly in antibiotic-rich environments, like hospitals, there is more room and resources for the resistant ones to thrive, passing along only the mutated genes that help them do so.
Reproduction isn't the only way to do this. Some can release their DNA upon death to be picked up by other bacteria while others use a method called conjugation, connecting through pili to share their genes. Over time, the resistant genes proliferate, creating entire strains of resistant super-bacteria.
End transcript: Video 6
Video 6
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In your own words, what is antibiotic resistance?

Discussion

Bacteria have developed ways to defend themselves against the antibiotics that other microbes produce. When bacteria can withstand attack by the antibiotic, they are termed resistant to that antibiotic.

Bacteria can be innately resistant or acquire resistance. (You will learn more about this in the module Introducing antimicrobial resistance.) The first, innate resistance, is a natural state of some bacteria. For example, some organisms may have innate resistance because the antimicrobial cannot pass the bacterial cell wall. Examples of innate resistance include Enterococci, which can withstand the effects of cephalosporins, and Klebsiella species that are not susceptible to penicillin V.

Resistance can also be acquired. The two major ways of developing acquired resistance are through genetic mutation or through gene transfer. Bacteria mutate with a high frequency: not all of these mutations lead to antimicrobial resistance, but some do. Even the slightest selective advantage brought about by a mutation can result in an organism out-competing its neighbours. Bacteria with a resistance gene can transfer it to another bacterium, which then acquires resistance (gene transfer).

Remember: bacteria are the ones that get resistant to antibiotics – not people, animals or plants.

The term ‘antimicrobial resistance (AMR) is used to describe this phenomenon. Although it technically includes resistance to all microbes, in this course it will generally be used to refer to antibacterial resistance.

In Section 4 we will look at the development and drivers of resistance in more detail, but first let’s take a moment to think about what this means for modern medicine (human and veterinary), and agriculture at the global scale.

3 The problem of antibiotic resistance

3.2 Consequences of resistance