Microbiology

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It's one of my units at uni and what i'm thinking is to sort of do my revision notes
electronically?
We'll see how this one works out, cause here's the first one:

 

Antibiotics= chemotheraputic agents, and they are of course used to treat diseases.
i.e. A chest infection you might get Amoxycilin, i used to get this ALL the time from my doctor. For anything and
everything. You don't get antibiotics for illnesses such as the common cold.

Why not?
Because the common cold is caused by a virus and antibiotics do not work on viruses, they only work on bacteria.

So what do they do?

  • They interfere with the metabolism of the microbe- but without affecting the host cell (your cell) too much.

  • Exploit intrinsic differences between the mircrobial cell and the host cell. Selective Toxicity

This means that antibiotics are specific for certain bacteria and know the difference between Prokaryotic and
Eukaryotic.

Eukaryote Prokaryote

Cells DNA contained DNA is not contained
within a membrane within cell membrane

All other organisms DNA often called plasmid
(Mitochondria etc)
are contained within
cell membranes

Animal Cells Bacteria
Plant cell

This is very helpful because it stops the antibiotic from harming/killing the host cell too as they are of different
natures/forms.

 

A list of Antibiotics and the places in which they act:

Penicillin, Cephalosporins, Bacitracins -----> Cell Wall
Chloramphenicol, tetracyclines, Erythromycin, Streptomycin -----> Protein Synthesis
Rifamycin, Nalidixic acid -----> Nucleic Acid
Polymxins -----> Cell Membrane
Sulphonomides -----> Cytoplasm


There are pretty much two types of antibiotic:

Broad-spectrum and Narrow-spectrum, Which means that the antibiotic acts on a wide range of both
Gram +ve and Gram -ve bacteria or that they act on specific bacteria respectively.

 

E.G: Penicillin G ---> Penisillium chrysogenum (produced by)

This antibiotic is effective against such diseases as Syphilis and Gonorrhoea, menigicoccal meningitis.
These are Gram +ve coccal infections.

 

What does it do?

 

Inhibits formation of PEPTIDOGLYCAN which is only produced in the CELL WALL.
Mammals cells do not have cell walls and so this antibiotic is effective for human use.

 

What does the peptidoglycan do?

The cell walls purpose is to protect the cell membrane and the peptidoglycan protects the cell membrane;
The cell membrane would ususally burst if put under High intracellualr osmotic pressure. So without the
peptidoglycan
being produced, the cell wall is rendered useless and the cell membrane will burst killing the cell.

 

PENICILLIN

The most commonly used antibiotic in general therapy, but Penicillin G is the most effective, naturally produced
antibiotic.

 

On the down side, penicillin is unstable in acid (Acid Labile) and can be destroyed in enzymes (Beta-Lactamases)

It is UNSUITABLE FOR ORAL USE. It has to be administered using the parenteral route, which means an injection:
skin/muscous membrane must be pierced. They are used to treat Gram +ve bacterium usually as it is more
effective
It is also used to treat gram -ve however.

 

Semisynthetic Penicillins:

 

Penicillin V: This can be administered orally and is a broad-spectrum antibiotic. less effective at treating Gram -ve
bacteria however is very good at treating Gram +ve bacteria. It is not active against Beta-Lactamase.

 

Semi-Synthetic Methicillin is a narrow-spectrum antibiotic used for treating Gram +ve bacterium, especially beta-
Lactamase producing bacteria as it is un-susceptible to the beta lactimase enzyme. It can only be administered
Parenterally (needle) and is No longer used for patients.

 

Cloxacillin: Used to treat beta-lactamase producing bacteria, Gram +ve bacteria. Can be taken Orally.

 

Ampicillin: Effective against both Gram +ve and -Ve (some) bacteria and especially good against beta-lactamase
producing
bacteria. it can be taken orally.

 

Carbenicillin: Mainly gram -Ve but some restricted Gram +ve use. They are susceptible to beta-lactimase
breakdown
and is acid-labile. Orally administered.


Streptomycin -----> Streptomyces griseus
Broad spectrum
It is used to cure Tuberculosis



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