Antibiotics

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Antibiotics
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What are Antibiotics?

• Antibiotics against life
• Antibiotics are molecules that stop microbes,
  both bacteria and fungi, from growing or kill
  them outright.
• Antibiotics can be either natural products or
  man-made synthetic chemicals.

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• Most of the antibiotics identified over the past
  60 years have been natural products produced by
  one microorganism, within a particular
  environment, to affect neighbouring microbes.
• Can cause microbe death or regulate the growth of
  the neighbouring microbes.
• These antibiotic agents are produced by both
  bacteria and fungi.

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• Depending on the microbe affected by the
  antibiotic it will be classified as
  either Antibacterial
• Antifungal
• There are almost no therapeutically useful agents
  that are effective as both.
• Anti-bacterial antibiotics can be categorized
  based on their target specificity
  "narrow-spectrum" antibiotics target particular
  types of bacteria, such as Gram-negative or
  Gram-positive bacteria, while broad-spectrum
  antibiotics affect a wide range of bacteria.

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Administration

• Previous treatments for infections often
  consisted of administering highly toxic chemical
  compounds such as strychnine and arsenic.
  Antibiotics from microbes have relatively few
  side effects and high effective target activity.
• The antibiotics have to come into contact with
  the undesired microbes in order to have an
  effect.
• Can be administered
• Orally
• Intravenously
• Topically

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Mechanism of Action

• Antibiotic action can be split into 2 mechanisms
• Bacteriostatic
• Bacteriocidal

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Bacteriostatic

• Bacteriostatic antibiotics inhibit growth and
  reproduction of bacteria without killing them.
• Bacteriostatic agents must work with the immune
  system to remove the microorganisms from the
  body.
• Bacteriostatic antibiotics hamper the growth of
  bacteria by interfering with bacterial
• Protein production
• DNA replication
• Cellular metabolism

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Bacteriocidal

• A bacteriocide is a substance that kills the
  bacteria of choice and, preferably, nothing else.
• Microbe death is usually achieved by disruption
  of the bacterial cell membrane leading to lysis.

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Penicillin
Penicillin is one of the earliest discovered and
widely used antibiotic agents, derived from the
Penicillium mold. In 1928, Sir Alexander Fleming
observed that colonies of the bacterium
Staphylococcus aureus could be destroyed by the
mold Penicillium notatum, proving that there was
an antibacterial agent present.
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Penicillin

• Use of penicillin did not begin until the 1940s
  when Howard Florey and Ernst Chain isolated the
  active ingredient and developed a powdery form of
  the medicine.
• Penicillin is a group of ß-lactam antibiotics
  that work by inhibiting the formation of
  peptidoglycan cross-links in the bacterial cell
  wall weakening the cell wall of the bacterium and
  leading to lysis.
• Penicillin is a bacteriocidal agent.

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Antibiotic Production

• Since the first pioneering efforts of Florey and
  Chain in 1939, the importance of antibiotics to
  medicine has led to much research into
  discovering and producing them.
• Despite the wide variety of known antibiotics,
  less than 1 of antimicrobial agents have any
  medical or commercial value.
• In order to identify the useful antibiotics, a
  process of screening is often employed. Using
  this method, isolates of a large number of
  microorganisms are cultured and then tested for
  production of diffusible products which inhibit
  the growth of test organisms.

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Antibiotic Production

• Antibiotics are produced industrially by a
  process of fermentation, where the source
  microorganism is grown in large amounts.
• As the antibiotics are produced by the
  microorganisms they have to be removed to ensure
  they do not effect the bacterial population.
• Certain bacterial species are selectively mutated
  to produce the maximum amount of the antibiotic
  agent.

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Side Effects

• Side Effects can vary widely from nausea to fever
  to a major allergic reaction.
• One of the more common side effects is diarrhoea,
  sometimes caused by the anaerobic bacterium
  Clostridium difficile, which results from the
  antibiotic disrupting the normal balance of the
  intestinal flora.

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Misuse of Antibiotics

• The most common form of misuse is failure to
  finish the course of the antibiotic.
• This can lead to populations of bacteria
  developing antibiotic resistance.
• E.g. MRSA
• C. Difficile

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Antibiotic Resistance
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How does resistance develop?

• The large number of bacterial cells in a
  population leads to the emergence of mutants.
• If a mutation confers a selective advantage for
  survival, e.g. can survive in the presence of an
  antibiotic, then the bacteria will survive and
  grow as its neighbouring bacteria die.
• In general, the more widely used the antibiotic,
  the more chance there is of a resistant strain of
  bacteria emerging.

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