Antibiotics: Chemical agents
of Biotic origin able to cure infectious diseases.
Antimicrobial Drugsare antimicrobics synthesized in a laboratory. These
drugs are made by man. Antibiotics are (originally) produced by a microorganism
in small quantities that will inhibit growth or even kill another organism.
Antibiotics are usually from either Fungi or Bacteria.
Antimicrobial drugs are designed
to act within the host (us). They must kill the invading pathogen without
damaging the host. This is termed selective toxicity. This is usually
based upon biochemical differences between the host and the invading microbe.
There are three major differences
between the host and invader that can be exploited.
- Unique Enzymes
- Shared Enzymes Essential
to Pathogen but not to the host
- Different Pharmacological
Properties within the host and pathogen.
An important early antibiotic
was discovered by Alexander Flemming (1927). Flemming was searching for
antimicrobic agents. One day, he discovered a plate of S. aureus contaminated
with a mold (Penicillium = genus). He noticed that there was a “zone of
inhibition” around the mold where no bacteria were growing. The substance
around the mold was characterized and later termed Penicillin. Penicillin
was first used to cure an Oxford policeman with a Staph infection.
Some common mechanisms of Antibiotic/Drug
- Inhibition of cell wall
synthesis - Affects the bacterial cell wall, thus, causing weak points
in the cell wall Examples: Cycloserine and Penicillin
- Inhibition of Nucleic Acid
Synthesis - Blocks synthesis of the raw materials involved in the generation
of DNA and RNA Inhibits replication and can stop transcription Example:
Para-aminosalicyclic acid (PAS)
- Inhibition of Protein Synthesis
- Will react with the ribosome-mRNA complex Examples: Streptomycin,
- Interferes with the function
of the cell membrane - Interacts with the phospholipids of the membrane
and can lead to metabolic insufficiency or lysis of the cell. Antifungals
work in this way. Animal cells have cholesterol in their membranes and
fungi have ergosterols in their membranes. Thus, target the ergosterols.
- Inhibition of Metabolite
Synthesis - Specific Metabolites can be inhibited from forming via inhibitors
(competitive and noncompetitive). Sulfonimides = Sulfa Drugs. This is
a very important compound for folic acid synthesis by bacteria, and
folic acid is important for purine and amino acid synthesis. The sulfa
drugs compete with PABA (competitive inhibition) for the active site
on the enzyme.
Vancomycin, Rifamycin, Viomycin, Erythromycin - inhibit Protein
Polymixin B, Bacitracin
- Deterioration of bacterial cell membrane
Gentamicin - Induces abnormal protein synthesis
- Inhibits Cell Wall Synthesis
In laboratory tests, there
is a simple interaction between the antimicrobial and the microorganism.
In the patient, however, the antimicrobial enters into highly complex
interactions with the body and microorganism, a relationship entirely
different from that in vitro. Furthermore, the eventual success of antimicrobial
therapy in each case will be influenced by such factors as:
- the immune response of the
- the type and site of pathological
- the extent of inflammation
- the local circulation and
- the number of organisms
- the bacterial virulence
- the ability of the antimicrobial
to penetrate and concentrate in effective levels at the site of infection
US Cases Of Resistant
Bacteria Cause For Concern
CDC Study Documents
Dangerous Rise By Linda A. Johnson
The Associated Press Dec. 27 — A sometimes-lethal type of bacteria
that causes many cases of pneumonia, bloodstream infections and
other illnesses is rapidly becoming resistant to antibiotics, a
government study found.