Overview – Bacterial Protein Synthesis Inhibitors (Antibiotics)

Many bacteria are inherently resistant (intrinsic resistance), while others develop resistance to common antibiotics such as penicillin or fluoroquinolones. For the treatment of infections caused by these pathogens, selective antibiotics, pathogen-specific narrow-spectrum antibiotics should be used. Life-threatening infections should be treated with broad-spectrum antibiotics before identification of the pathogen. This article provides an overview of reserve antibiotics, their pharmacodynamics, indications and adverse effects.

00:00
Let's move on to another
category ofantibacterial agents,the Bacterial Protein Synthesis Inhibitors.
00:08
So the bacterial protein
synthesis inhibitors are narrowspectrum agents.
00:15
They act either on the 50 S
subunit such as linezolidor streptogramins
or lincosamines.
00:22
Or the broad spectrum agents
that are like the macrolides.
00:26
and chloramphenicol.
00:28
Other broad spectrum agents
that act on the 30 S subunitinclude the tetracyclines,
the aminoglycosides.
00:36
Now let's just quickly
do some definitions.
00:40
Because we need to do
this before we go on.
00:42
There's something called
as post-antibiotic effect.
00:45
So this is an anti-ineffective
effect that lastsafter the elimination
of the antibiotic from the body.
00:50
That's often because we have
some kind of, I wouldn't saypermanent but long lasting
effect in this caseon the 50
or 30 S subunits.
00:59
Bactericidal means
that it kills bacteria.
01:03
Bacteriostatic means that it
just stops the bacteriafrom replicating but doesn't kill them.
01:09
So the bacteria are still
alive but the numbersaren't increasing.
01:13
So the other immune mediated,
killing of the bacteriacan occur unimpeded.
01:19
The 70 S ribosomal mRNA subunit
is composed of a 50 Sand a 30 S.
01:28
Okay, I know 50 plus 30 is 80.
01:32
And how come 50
plus 30 equal 70.
01:34
Don't worry about it, the point
is that the 50 Sand the 30 S make up 70 S unit.
01:40
Time dependent agents.
01:43
So these are drugs that have
increased killing activitywith time.
01:48
This is different from the
concentration dependent killingwhere the drugs have increased
killing activitywith concentration.
01:55
So there you have some basic
definitions and we're goingto be using them as we go
forward in this lecture.
02:03
Let's go on to
the 70 S ribosomal unit.
02:10
The 70 S ribosomal unit is made
up of 50 S and the 30 S units.
02:15
Now, this is a hamburger.
02:17
Think of it is as
a hamburger bun.
02:19
So 50 S is top of the bun
and the 30 Sis the bottom of the bun.
02:22
So the 30 S is
smaller and flatter.
02:24
The 50 S is bigger and puffier.
02:26
Now how this works is that you
have this charged transfer tRNAon the end there.
02:33
Bringing in the 7th amino acid.
02:36
You can see the 7 in there,
that's the amino acid.
02:38
So the charged transferRNA
and sits on top of the mRNA,or messengerRNA.
02:44
And the messengerRNA is the base
that determines what the codingis going to be for the protein.
02:51
Let's pretend for a moment that
this particular protein is,or I don't know a protein
involved in metabolism.
02:57
There's a specific code
that's coded by mRNA.
03:00
And it tells the transferRNA
which amino acids to bring in.
03:05
As it goes through the
hamburger, it's as if you hada slice of cheese through
the hamburger buns,you get different coding.
03:13
And you have a very specific
sequence that makes upthe protein.
03:18
So the protein is the sort
of the chain of blue circlesthere.
03:22
Kind of like a string onion
coming out of the hamburger.
03:25
So that protein is very
specifically configured based onthe characteristics
of the messengerRNA.
03:32
Now the unchanged, sorry
uncharged transferRNA is thendiscarded and eventually becomes
charged and then it grabsanother amino acid.
03:43
Now, the drugs we're going to
talk about act at differentpoints in this 70 S
ribosomal unit.
03:50
So for example, chloramphenicol
blocks the transpeptidationwhich is the joining
of the two amino acids.
03:57
The macrolides also block
transpeptidationbut in a slightly different area.
04:03
The tetracyclines binds to 30 S
subunit and prevent bindingof incoming transferRNA.
04:10
So they actually stop, you
know transferRNA number 7from joining.
04:15
Linezolid has a unique site
that inhibitsinitiation complex formation.
04:21
So initiation complex is
the very first reactionthat brings the 30 S
and the 50 S together.
04:27
And allows everything
to start working.
04:29
On the other end
of the production line there,the streptogramins block exit ports for polypeptides.
04:36
So new ones can't come inand overall transcription
is inhibited.

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