Mrs. Stewart
Medical Interventions
Central Magnet School
GRAM (-)
GRAM (+)

Thin layer of peptidoglycan

Thick layer of
peptidoglycan

Lipopolysaccharides
(endotoxins)

Stain blueish - purple

Stain red
Bacteria are stained with two stains:
1. Crystal Violet stain (blue/purple)
2. Fuchsin counterstain (red)
Gram –
Gram +

Blueish-purple

Red

Peptidoglycan layer
absorbs the crystal violet
stain

LPS cell wall prohibits
peptidoglycan layer from
absorbing crystal violet
stain (absorbs counter
stain)

What cellular components do some bacterial
cells have that make them powerful
pathogens? Explain.
GRAM -

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 – wound
infections that lead
to many amputations
or sepsis

Sepsis – bacterial
infection in blood
stream – leads to
organ system failures

The early antibiotics = natural products of
other microorganisms (fungi or other
bacteria)

Now = created synthetically (chemically
altering existing natural products)

Depends on
the bacteria
Gram +
OR
 Gram 

Bactericidal – Kills the
bacteria

Bacteriostatic – inhibits
growth & reproduction
* The body’s natural defenses
can usually take it from there




Beta – Lactam
Fluoroquinolones
Tetracyclines
Sulfanomides

Disrupt the synthesis of peptidoglycan
thereby inhibiting cell wall synthesis &
damaging cell wall integrity

Broad spectrum (can work against + or -)

Bactericidal

Example: Penicillins

Why are penicillins often more effective
against gram positive than gram negative
bacteria?

Inhibit topoisomerase enzymes which
prohibit DNA replication and protein
synthesis

Broad spectrum – effective against + and -

Bind the 30s ribosomal subunit,
blocking the attachment of
tRNA, thereby inhibiting protein
synthesis

Broad spectrum – effective
against + and -

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

Why is it important to understand the
structure of a bacterial cell when developing
an antibiotic?

What class of antibiotics would you prescribe
for Sue? Explain.

Bacterial
infections only

Antibiotics target
bacteria and a
few parasites.

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

Antibiotics are
not effective
against viruses.

Most colds
and sore
throats are
caused by
viruses

How do antibiotics function without harming
the surrounding human cells?

NO

That leads to antibiotic resistance due to
overuse

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

Ear Infections

MRSA

TB – Tuberculosis

Strep throat