Download Introduction of antimicrobials.pps

And
Penicillins

Though antimicrobials have been around forever,
we have only known about them since the late
1920’s.

A fungal contaminant on a bacterial culture
inhibited the organism from growing. The
contaminant was Penicillium notatum. This
occurred in Dr. Alexander Flemings lab.

It was several years before this diffusible
bacteriolytic substance could be sufficiently
produced and used.

Though penicillin got us through, WWII it was clear
that it was not effective against all microbes.

Soil microbes such as streptomycin have been used to
produce many more antibiotics. A culture of this
organism smells like dirt. The best example is the
smell under your house. This branched bacteria is
between bacteria and fungus.

Organisms need to protect their ‘personal space’ and
they do so by producing antimicrobials.

Genes that help an organism become resistant to
a particular antibiotic may be found on their
chromosome or on plasmids.

Some whole groups of organisms are inherently
resistant because of a chromosomal gene. It is so
prevalent that the resistance pattern can be
used to help identify the organism.

Resistance is many times acquired. Genes,
especially on plasmids pass from organism to
organism easily or are passed via viruses.

Promiscuity is rampant.

All penems have the structure above. The
square is called the beta lactam ring.
Penicillin is one of many in this beta
lactam group and is produced by a fungus.

Penicillin is generally active against
gram positive organisms but is good
against many more. Examples are syphilis
and GC.
Penicillium chrysogeum
is the organism which
produces penicillin today.

Given orally though not
all is able to withstand the
acid in the stomach.


Given IV also

Penicillins inhibit the peptidoglycan cross-linking step in the biosynthesis of
the bacterial cell wall . The result of this cross-link inhibition is an unstable
bacterial cell wall which can more easily break and compromise the bacterial
cell.
Penicillin V
Procaine benzylpenicillin – IM (the procaine is to dull the pain of the shot)
Benzathine benzylpenicillin- IM



 http://student.ccbcmd.edu/courses/bio141/
lecguide/unit1/prostruct/penres.html
 Go
to this site to watch how drugs with beta
lactam rings keep transpeptidases from
crosslinking parts of the cell wall
Ampicillin is effective against gram positives
but also gram negatives. It was introduced
in the early 1960s and is still used today.
The difference is the amino group seen
above. That addition helps it penetrate the
cells wall of gram negatives.
Amoxicillin is an aminopenicillin like
ampicillin and is adsorbed well, better
than most penicillin. This is the most
commonly prescribed drug for children. All
of you have had this drug.
You may know the drug Augmentin.
Augmentin = Amoxicillin + Clavulanic Acid
These are usually pink and taste good.

Many organisms produce an enzyme called betalactamase. This enzyme cleaves the beta-lactam ring
inactivating the drug.

New drugs resistant to the enzyme such as methicillin were
produced.

Methicillin is not used today because it has been replaced
with more stable drugs but the terminology remains.
Nafcillin, oxacillin, (flucloxacillin and dicloxacillin) are
used.

If an organism such as Staphylococcus aureus is resistant to
this group of drugs, it is termed ‘methicillin resistant’.
This is not a good thing because it means that there are
only a few remaining antibiotics that may be used to treat
the patient.
Just another example to show that
penicillins are not just for gram positives,
this drug is used to treat Pseudomonas.


You may have heard the term ‘swimmers ear’. This is
a general term but can mean an ear infection with a
water bug called Pseudomonas aeruginosa. It grows
out with a green pigment on media and even
produces it at the site of infection.

This has to be given IV or IM and like Augmentin is
given with a beta-lactamase inhibitor. (Clavulanic
acid and tazobactam make the drug they are given
with more resistant to the enzyme beta-lactamase)