Animal health - antibiotics and microbes

• Pre-Antibiotics: Moulds, Heating & Microbial

  • Moulds used in ancient Greece and China
  • Herbs in Iraq
• Microbial Dates:

  • 1917 - Greig-Smith Welsch found antinomycetin from Streptomyces
  • 1937 - Welsch isolated Antinomycetin from streptomycetes
  • 1939 - Dubos isolated Tyrothricin
• First therapeutic antimicrobials were not antibiotics
• Chemicals 1: Syphilis

  • 1854 - 1915
  • Paul Ehrlic
  • tested 600 arsenic compounds
  • in 1908 found compound 606 - Arsphenamine
  • effective against syphilis
• Chemicals 2:

  • 1895 - 1965
  • Gerhard Domagk
  • 1935 - Prontosil
  • developed sulphonamides effective against: pneumonia, meningitis, Gonorrhoea
• Penicillin:

  • discovered by Alexander Fleming
  • Staphylococcus culture went mouldy
  • mould cleared bacteria around itself
  • extracts remained effective at 800th dilution
• Antibiotics definition:

  substances that kill or damage pathogens but do not harm other cells
• what are antibiotics?

  • microbes but not organic acids, peroxides or alcohols
  • selective toxicity for invaders
• Antibiotic Microbes example

  Streptomyces:

  • filamentous and important bacteria
  • source of 75% described antibiotics
  • DNA with high Guanine - Cytosine
  • secondary metabolism
  • largest number of genes
• Antibiotic microbes example:

  Fungi / moulds

  • 20 % of all antibiotics are fungal
  • all chemotherapeutic antibiotics
• antibiotic microbes example:

  True bacteria = Bacillus

  • 5 % of all antibiotics
  • almost all from Bacillus genera
• Test antibiotics:

  1. Sample, grow and isolate microbes
  2. test isolates as antimicrobials:
  3. add to pathogen plate, incubate
  4. clear = inhibition zone
• Test antibiotics: MIC (minimum inhibitory concentration)

  • prepare liquid media & add antibiotics
  • inoculate with test microbes
  • incubate
  • turbid culture = pathogen growth = no inhibition
  • clear culture = no pathogen growth at lowest dose = MIC
  • further tests using nutrient agar plates to confirm MIC
• Test antibiotics: Disc diffusion test

  • nutrient agar medium
  • microbial growth
  • red paper discs with antibiotics
  • clear zones around discs = antimicrobial
• gene technology = microbial

  • identify genes in microbes
  • gene mutation to enhance yield
  • gene modification and amplification
  • extraction and purification
  • test for potency, toxicity, safety and efficiency
• microbial antibiotic production summary

  • collect sample to isolate microbes
  • identify microbes
  • isolate colonies and test MIC
  • test anti bacterial chemicals
  • purify
  • re test - in vitro and in vivo
  • mass produce using fermenting vessels
  • mix with carriers and binders
  • antibiotics produces
• How antibiotics work: target bacterial cell: BACTERIAL CELL

  • in a bacterial cell ions and metabolites have higher conc inside than outside
  • more osmotic pressure inside but
  • cell membrane is delicate so covered with rigid cell wall
• How antibiotics work: bacterial cell wall:

  composed of:

  • peptidoglycan
  • glycan
  • tetra-peptide
• how antibiotics work: attack bacterial cell wall

  • five major antibiotic groups based on their target sites
• antimicrobial classification: Bactericidal:

  • kill or dissolve pathogen / bacteria by breaking cell wall
  • penicillin, cephalosporin, vancomycin
• antimicrobial classification: Bacteriostatic

  • suppress or stop bacterial growth:
  • distort DNA replication
  • interfere with protein synthesis
  • stop folic acid synthesis
  • rely on host defence
  • example: tetracyclines, chloramphenicol, macrolides
• Antibiotic examples: B-Lactam

  • similar to penicillin
  • lactam molecule with an amide bond within a four member ring
  • involved in amide N and Carbonyl carbon
• antibiotic examples: Aminoglycosides:

  • bind to 30 S ribosomal sub-unit causing misreading by tRNA
  • bacteria unable to synthesis protein for its growth
  • treat serious bacterial infections via = intravenous or intramuscular
  • used orally to treat = intestinal infection and topical infections
  • example: streptomyces, Micromonospora
• antibiotic examples: Macrolides = mycines

  • a lactone ring with deoxy sugars (cladinose & desosamine)
  • lactone ring may have 14, 15, or 16 members
  • a polyketide class of natural products
  • examples = erythromycin, azithromycin, clarithromycin
• when to use antibiotics: Therapeutic

  • high doses for short period = treat infections and diseases
  • example: bacterial enteritis in swine, anaplasmosis in cattle
• when to use antibiotics: sub-therapeutic

  • small doses in feed or water to prevent disease
  • example: 200g / tonne will cure low level infection, prevent disease outbreak, bacterial resistance
• benefit of antimicrobial use in animals:

  • disease control and animal welfare
  • nutrient sparing, improved feed and water intake
  • reduced toxic wastes products
  • better digestion and absorption
  • quality food for consumers
• why use alternatives?

  • in hospitals resistance to antibiotics is high
  • existing low cost antibiotics fail against frequent infections
  • newer more expensive antibiotics face more resistance
• antimicrobial resistance:

  clinical resistance to a drug occurs when the MIC of an agent specific bacteria exceeds the safe level of MIC in vivo
• antimicrobial resistance: occurs by:

  • mutation in gene, sensitive or resistant to a drug
  • or
  • gaining chromosomal DNA carrying a resistant gene
• Antimicrobial resistance: two types

  • cross resistance = a single mechanism gives resistance to multiple antimicrobial agents that are closely related
  • multiple resistance = multiple mechanisms give resistance to unrelated antimicrobial agents
• major mechanisms of antimicrobial resistance

  1. altered permeability of antimicrobials due to: antimicrobial can't enter the bacterial cell and active export of antimicrobial from cell
  2. inactivation of antimicrobials by enzymes
  3. mutated target site that stops antimicrobial binding
  4. replacement of sensitive pathways
• Example of antimicrobial resistance: tetracycline resistance

  • inhibits tRNA & bacterial growth by binding to 30 S ribosome
  • this binding is reversible = bacteriostatic
  • infectious bacteria resist tetracycline by at least two routes:
  • efflux and ribosomal protection
• tetracycline resistance: 2 routes

  • efflux = a resistant gene encodes a membrane protein that pumps tetracycline out of the cell via artificial plasmid pBR322
  • ribosomal protection = another gene encodes a protein which binds to ribosome & resists tetracycline action on ribosome
• antibiotic resistant examples:

  • 1950s = staphylococcus aureus treatable with penicillin but today = most strains resistant
  • 1980s = 50% of people with TB had resistant strain
• antibiotic resistance:

  • resistant genes transfer between bacteria = bacteria never exposed to antibiotics acquire resistance from others - DNA transduction
• alternatives to antibiotics:

  • stabilise gut - optimise beneficial microbes
  • dietary manipulation
  • pre - biotics
  • pro - biotics
  • directly fed microbes
• Alternatives: stabilise gut microbes: strategy:

  • balanced diet
  • gradual change of diet
  • stress free & hygiene housing
• alternatives: Stable gut microbes: benefits:

  • more resistant to pathogens
• alternatives: stabilise gut microbes: mechanisms

  • better attachment, digestion + protection
  • competitively exclude pathogens
  • occupy receptor sites via fimbrae - gut wall, oligosaccharides
  • inhibit pathogenic growth by releasing toxins