Bacteria and Antibiotics

Mrs. StewartMedical InterventionsCentral Magnet School

2 Classes of Bacteria

GRAM (-)

Thin layer of peptidoglycan

Lipopolysaccharides (endotoxins)

Stain red

GRAM (+)

Thick layer of peptidoglycan

Stain blueish - purple

What’s the difference?

Gram Stain

Gram +

Blueish-purple

Peptidoglycan layer absorbs the crystal violet stain

Gram –

Red

LPS cell wall prohibits peptidoglycan layer from absorbing crystal violet stain (absorbs counter stain)

Bacteria are stained with two stains:1.Crystal Violet stain (blue/purple)2.Fuchsin counterstain (red)

Think – Pair – Share

What cellular components do some bacterial cells have that make them powerful pathogens? Explain.

Neisseria Meningitidis

GRAM -

How do we treat bacterial infections?

Antibiotics are drugs used to treat infections caused by bacteria.

Antibiotic - A substance produced by or derived from a microorganism and able in dilute solution to inhibit or kill another microorganism

History of Antibiotics•1928- Alexander Fleming

•Accidentally discovered penicillin

•Left lab untidy for a month and went on vacation

•Came back and found a fungus growing in one of his bacterial cultures. Fungus was inhibiting the bacteria.

•Fungus = penicillium notatum

•Later named: penicillin

Gangrene and Sepsis - WWI

Gangrene – wound infections that lead to many amputations or sepsis

Sepsis – bacterial infection in blood stream – leads to organ system failures

Penicillin

Where Do Antibiotics Come From?

The early antibiotics = natural products of other microorganisms (fungi or other bacteria)

Now = created synthetically (chemically altering existing natural products)

Which antibiotic is prescribed?

Depends on the bacteria

Gram +OR Gram -

How Do Antibiotics Work?

Bactericidal – Kills the bacteria

Bacteriostatic – inhibits growth & reproduction

* The body’s natural defenses can usually take it from there

Classes of antibiotics

Beta – Lactam Fluoroquinolones Tetracyclines Sulfanomides

Beta – Lactam

Disrupt the synthesis of peptidoglycan thereby inhibiting cell wall synthesis & damaging cell wall integrity

Broad spectrum (can work against + or -)

Bactericidal

Example: Penicillins

Think – Pair – Share

Why are penicillins often more effective against gram positive than gram negative bacteria?

Fluoroquinolones

Inhibit topoisomerase enzymes which prohibit DNA replication and protein synthesis

Broad spectrum – effective against + and -

Tetracyclines

Bind the 30s ribosomal subunit, blocking the attachment of tRNA, thereby inhibiting protein synthesis

Broad spectrum – effective against + and -

Sulfa (sulfonamides) 1st class of antibiotics ever used

Structurally similar to PABA – a substance that the bacteria use to synthesize folate (folic acid)

Inhibits the synthesis of folic acid (Folate)

folate is necessary for DNA synthesis

No DNA synthesis (replication) = No cell division

Think – Pair – Share

Why is it important to understand the structure of a bacterial cell when developing an antibiotic?

Think – Pair – Share

What class of antibiotics would you prescribe for Sue? Explain.

When are antibiotics prescribed?

Bacterial infections only

Antibiotics target bacteria and a few parasites.

Why don’t antibiotics work on viruses?

They do not share the same structures

Viruses consist of a hereditary material (DNA or RNA) surrounded by a protein coat or fatty envelope.

They do not have any organelles – they hijack host cells to produce more DNA/RNA or proteins

What type of infection is it?

Antibiotics are not effective against viruses.

Most colds and sore throats are caused by viruses

Think – Pair – Share

How do antibiotics function without harming the surrounding human cells?

Should we take antibiotics if we are

unsure what the pathogen is? NO

That leads to antibiotic resistance due to overuse

How does overuse lead to resistance?

There are more bacterial cells in/on your body than there are human cells

Antibiotics will target all susceptible bacteria – not just the spot of infection

All bacteria living within your body will either die (susceptible) or will live (resistant) Survival of the fittest

Examples:

Ear Infections

MRSA

TB – Tuberculosis

Strep throat