Lecture 2- Antimicrobials and antimicrobial action

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En provenance du cours de Technical University of Denmark (DTU)

Antimicrobial resistance - theory and methods

527 notes

Technical University of Denmark (DTU)

Antimicrobial resistance - theory and methods

527 notes

The course will cover the topics related to antimicrobial resistance with basic definitions and overview on antimicrobials their use and the emergence and spread of resistance. The course will guide you through the concepts and the importance of resistance spread and dissemination and how that happens. It will show you how bacteria become resistant and which mechanisms they might use for this. And as part of the course you will also receive some training in methods for antimicrobial susceptibility testing (AST) and detection of specific resistance in the microbiological laboratories with the basic methods available and with focus on the obtention of good quality results which can be interpreted and used for different purposes. Additionally, it will show you how to use genomic analysis tools to analyze whole genome sequencing data to detect resistance genes (and or other genes of interest) in a simple and easy way using online tools freely available. In the new new version an additional module including detection of specific resistance mechanisms was added. After this course you should be able to: 1. Describe the most important families of antimicrobials and mode of action 2. Understand the basic concepts of antimicrobial resistance from several perspectives (clinical, research and microbiological) 3. Enumerate and describe how bacteria can become resistant and the mechanisms that may be involved in that process 4. Describe how antimicrobial resistance emerges and spreads around the world including concepts of antimicrobial resistance transfer, selection and dissemination 5. Enumerate the methods used for antimicrobial susceptibility testing (AST) 6. Compare dilution and diffusion methods and know the basic techniques of agar disk diffusion, broth dilution and agar dilution methods 7. Have detailed theoretical knowledge on how to perform the main methods in a laboratory 8. Know the basic concepts about analysis and interpretation of results of AST, including different breakpoints, cut-off setting and their applications. 9. Understand the importance and related concepts related to quality management and quality assurance method standardization, applied to AST 10. Relate the information obtained in this course with real cases of resistant bacteria spreading in patients, the community, animals or the environment 11. Relate the phenotypical results with results from genotyping using molecular techniques for detection of resistance mechanisms 12. Understand the concept and be able to apply genomic analysis tools used to detect resistance genes and other relevant genes from Whole Genome Sequencing (WGS) data (with demonstration of selected online tools) Disclaimer: Please note that the guidelines and methods referred or links included in these materials are updated when the videos lectures are produced and before the course is released, however these might become outdated with time.

À partir de la leçon

Module A- Antimicrobial and antimicrobial action

Antimicrobials and antimicrobial action ( includes two lectures and one quiz). Here you will learn a lot about antibiotics/ antimicrobials and you will know more about:what they are, where do they come from, what are the major groups and how can we classify them, how do they have an effect, how do they act on the bacterial cells

Lecture 1- Antimicrobials and antimicrobial classification24:59

Lecture 2- Antimicrobials and antimicrobial action16:09

Rencontrer les enseignants

Lina Cavaco
Ext Researcher
Copenhagen University- ICMM /Statens Serum Institut - Department for Bacteria, Parasites and Fungi
Pimlapas Leekitcharoenphon
PostDoc
Research Group for Genomic Epidemiology, DTU Food
Rene S. Hendriksen
Professor, PhD
Technical University of Denmark, National Food Institute, Research Group of Genomic Epidemiology
Valeria Bortolaia

[MUSIC]

Hello, everyone. My name is Lina Cavaco, and

I'm here to present you the second lecture of this course.

And this course is going to focus on antimicrobials and

antimicrobial resistance.

So this lecture is also one of the very basic ones to understand what

antimicrobial drugs do and

how they do what they are supposed to to kill and inhibit bacteria.

So we are going to give you some definitions and

show you how antimicrobials actually work.

So to start with I give you some outline and

really we are going to into looking into the bacterial cell.

And what are the targets for the drugs, the antimicrobial drugs.

Where they have taken their action, how they do that?

What are the modes of action?

And the modes of action in regards to the spectrum of activity,

so in regards to which bacteria they are able to kill and why they do so.

So, we are going to define a little bit around bacteria.

Don't be afraid.

If you don't have the basics of bacteriology,

I will guide you through it and we'll look into what happens in the bacterial cell.

This is a very busy slide I know, but I'm going to spend some time explaining you.

Let's think this is a bacteria.

This is a bacteria cell.

A bacteria is a prokaryotic organism.

So you have a cell membrane, a cell wall structure.

You have the DNA in the cytoplasm, there is no nucleus in the prokaryotic cells.

And you have all the machinery that the cell needs inside this bacteria cell.

And they will divide to procreate, to become daughter cells.

They will split into two and they will live their lives happily and

maybe some cause some disease one of the days.

Many bacteria are not causing disease but

antimicrobials are used for the ones that do.

So what we are worried about is the ones that are causing disease and

are dividing in the human or animal body.

And those we want to treat with antimicrobials.

As when we give antimicrobials,

they have action in some points on this bacterial cell.

And one of the main points and

starting from the first antimicrobial's discovered which was Penicillin and

the drugs related to Penicillin and other groups of drugs.

They act on the cell wall.

So, they act on the making of the cell wall that when the bacteria divides and

cannot make a new cell wall.

Then they just are killed because they cannot grow beyond this point.

Again when we want to inhibit the growth of bacteria, we can also act on their DNA.

So if they are replicating the DNA they are dividing the DNA to make two

chromosomes and to split into daughter cells,

we can also act there on the DNA replication.

And that's what some of the drugs that are used in treatment are doing as well,

like Fluoroquinolones and Metronidazole.

Then we can also interfere with the cell protein factory.

Cells, like every cell, needs protein to make protein to build up their systems.

And they will be doing this from the DNA and

transcribing the RNA and

this can be stopped by some of the drugs that we are using.

So some of the antimicrobials would interfere with the protein synthesis

either interfering with the RNA polymerase in this case or

they interfere with the protein synthesis as well.

But then, by inhibiting the ribosomal binding.

Also here,

that is the ribosomal binding is just that they bind to different targets.

Again, in this case, is a very specific target in relation to only gram-negative

bacteria, which is a specific group that have this outer cell membrane.

You act on this outer cell membrane.

Of course it wouldn't work on cells that don't have this one.

So, it only works on these gram-negatives.

And this is quite important groups as the Polymyxins and Colstin and

Amphotericim, and this is kind of an almost mechanical effect as a detergent.

This means also that these antimicrobial drugs are rather toxic, but they

are actually used in last-case resources when other antimicrobials don't work.

That's why we are quite worried nowadays,

where resistance to these have been found very very recently.

So at the last part, we have metabolism going on inside the cells and

for example, one of the important pathways inside the bacteria cell

is the production of folic acid.

And here you have several substrates going into this metabolism.

And several groups of drugs that we are using like Sulfonamides and

Trimethroprim, happen to be very alike with one of the intermediate substances.

So they mimic one of the substrates, and

therefore they stop this process from going on.

So in this case, they would interfere with the metabolism

inside the cells of one of the essential components.

So as you can see, well, there is a number of targets in the bacterial cell, but

there's not much more than that.

So actually, we are relatively limited.

Just to show in another way, we have some of the antimicrobial

groups and how they classify in relation to cell wall synthesis,

DNA, protein or inhibition of folic acid are here.

So there is just in writing in text what more or

less the same what I told you in the picture.

So, as you can see, there's not so many places where a drug could actually affect.

So in a way there is a limited number of targets.

This is Is something that limits also the pharmaceutical companies and

the researchers there to find new targets,.

There is no new targets, they have to invent new drugs

that still can act on these targets and get the bacteria killed by that way.

So and because I talked about cell wall synthesis and

there are differences in the cell walls.

If you don't have a background in bacteriology,

I must tell you that there are two big groups of bacteria.

The gram-positives which have a structure of a cell wall that is

quite different of the gram-negative ones.

And the basic differences is that while all bacterial have this internal membrane,

and then they have this thick layer of Peptidoglycan in the gram-positive cell

walls, and they don't have any other structure, any other outer membrane here.

So the drugs are able to pass this Peptidoglycan and act on the targets.

In relation to the gram-negative cell walls, it is a bit

different because there is this outer envelope this outer cell membrane.

And then the drugs would need to cross this,

which is a little bit more difficult.

And they are depending on some pores on this cell wall,

and these pores are regulated by some of proteins that are porous.

When the drug crosses this, then they would be able to cross this space and

act on the targets.

So there is some differences, and this makes a difference into which drugs you

can use for the gram-positives and which drugs you can use for the gram-negatives.

Of course if we use a cell-wall-synthesis-inhibiting

antimicrobial which should have a cell wall,

there's also some bacteria that just don't have it.

So they have a different structure.

So in those it would not work at all.

And for the drugs that act on the cell wall, there's still some that act on

better on gram-positives and better on gram-negatives.

So as I mentioned also for the RNA and protein synthesis,

there are several places where we can act.

While first there would be nucleotides in their genome, and

when we replicate the DNA you would have some DNA replication.

And when you want to make proteins there would be a RNA polymerase acting.

And there would be binding to the ribosome and

transcription into protein so that in the end we have protein.

If we want to inhibit the cycles, we can inhibit at the basic level.

At the DNA level, we can inhibit at the polymerase level,

or we can inhibit at the ribosomal level.

And that's what happens with these antimicrobial drugs.

So we have drugs that act on these several processes.

Again, in the DNA synthesis it's rather similar,

we also have one molecule of DNA that wants to replicate to two so

that we have divided the cell into two cells at some point and there are some

enzymes that act on this DNA replication and the structuring of DNA.

Essentially for example Topoisomerases that are acting on this super coiling and

if you bring in some drugs like the quinolones that act on this specific

target the Topoisomerases for example, we have

an effect here and the replication doesn't go so well.

The cell dies from that so it causes cell death.

As I tried to explain a little bit before in the very busy slide,

here it is much better explained.

This metabolic inhibition of the folic acid synthesis.

Folic acid is actually one of the vitamins that we might take as a human,

but in the bacteria they produce it themselves, so

they need to synthesize it in able to be living, and

they have this series of substrates and enzymes that interfere in this

metabolism so that they get tetrahydrofolic acid at the end.

And here you have these substrates that are very similar to some drugs.

So this PABA is very similar to sulphonamide.

So they mimic the substrate and stop the synthesis here.

And the Trimethroprine is quite similar to this dihydrofolic acid and goes in here.

So there would be action in the metabolism itself.

So when I talk about different antimicrobials and

their different action that also implies that antimicrobials when they get in

contact with different bacteria.

They might act a little bit different because the bacterial species and

the bacterial structure is a little different.

So we have some antimicrobials that are quite good.

And these are gram positive until, sorry, up to here.

And these are gram-negative bacteria.

So you have some that act more on one side and some that at more on the other side,

and we have also very large spectrum drugs that are able to act on almost every drug.

Actually, this should also be grey.

Because the Cephalosporins have a very, very broad spectrum as well.

We have drugs that are very broad spectrum, and those are the drugs

that we use as a choice when we don't know what the infection is, for example.

We use the narrow spectrum when we know exactly what we are dealing with and

when we want to have a good effect on that narrow spectrum.

So, if we think about the spectrum of the drugs,

we can have some classifications depending on the classes.

The first drugs, the Penicillins,

which are still used quite a lot, are more targeted for the gram-positive bacteria.

Because some of the gram-positives have been developing some resistance

we got some modifications of this drug that were chemically done

to target for example more staphylococci and

then we had some other modifications that we're to target more the gram-negatives.

So they were evolving a long time and new groups of these Penicillins came along.

Cephalosporins are also in the same class,

in the beta-lactams class as the Penicillins.

But they also have evolved from a rather low spectrum and

gram-positives only towards a very large spectrum in the third and

fourth generation that takes both gram-positive and gram-negative bacteria.

Again here carbapenems.

These are one of the very last resource antimicrobials.

When you get carbapenems in the hospital it's because you are very sick and

resistance have arised.

And that's where you, you will need to get a treatment with such a drug.

Its a very large spectrum and it is used in highly

resistant strains also and monobactams are part of this family, also large spectrum.

But not exactly as much as the carbapenems but close to.

Again, this is for

other groups of antimicrobials that target the protein or DNA synthesis.

Again, there's differences in the spectrum depending on which drugs you used.

The macrolides are more for the gram-positive, tetracyclines are quite

broad in spectrum, and fluoroquinelones are quite broad as well,

as well as aminoglycocides, Gentamicin for example.

And then we have a very specific drug, Metronidazol which is only used for

anaerobe, so bacteria that are not breathing oxygen but

are living on carbon dioxide sources.

So, just to summarize in a very large view of different groups of bacteria,

here we have the mycobacteria which includes the tuberculosis agent for

example, Mycobacterium tuberculosis and other.

This is a very specific group which have different wall structure,

so you need very specific drugs in here.

So here for example, you will use something like this that is only used for

mycobacteria, maybe some of the large spectrum drugs like

the amino glycosids have some effect there.

The gram-negative bacteria, where you have several groups acting on them.

The gram-positive which includes treatment with Penicillins and

some of the large spectrum drugs as well.

The Chlamydias are also another group that is rather specific which is

more dependent.

t's not as the defined

as other bacteria, it's a little bit different.

It is not targeted by many, maybe a little bit Sulphonamides and

Tetracyclines, and the Rickettsias which are intercellular bacteria also,

are only really affected by Tetracyclines.

As you see Tetracyclines actually take up a large group of bacteria, and some of

the others take the main groups are these that are causing the main infections.

So thank you very much for this lecture.

I hope you, you will follow us for the next ones.

[MUSIC]

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