Micro Bio Exam 3: Antimicrobial Drugs

• Chemotherapy def.


  Use of chemicals to treat disease
• Antibiotic def.


  substance produced by a microbe that inhibits another microbe
• Selective toxicity def.

  selectively destroying and finding pathogens w/o damaging host
• Who are some of the most renowned scientists and what was their contribution?

  Ehrilich & Hata: discovered slavarsan (arsenic-containing)

  Fleming: discovered penecillin

  Klaver, mietzsch, domagk: discovered prontosil (red dye)
• Natural antimicrobial drugs:


  compound isolated from organisms (mold, fungi)
• Semisynthetic antimicrobial drugs:


  chemically modified from a natural drug
• Synthetic antimicrobial drug


  all made in a lab, developed from a chemical not found in nature
• Narrow-spectrum drugs and applications

  affects a narrow range of microbial types, and used when you know what bacteria you are dealing with
• Broad-range drugs and their application

  affects a broad range of gram + or gram - bacteria, used when you don't know the specific bacteria being treated
• When is the dosage of a drug important?

  For safety purposes and so it doesn't interfere with other bacteria in the body.
• What is the route of admission of a drug?

  orally: convenient, but not easily absorbed by the GI tract into bloodstream

  injection: short time to reach a high concentration in plasma, but only used in health-care settings (intravenous or intramuscular)
• What variables can influence the side-affects of drugs?

  Half-life: the rate at which 50% of the drug is eliminated from plasma

  Selective toxicity: selectively kills or inhibits the growth of microbial target while causing minimal or no harm in the host

  Toxicity: side effects casued by the drug

  Drug tolerance: some people are more tolerant
• Significance of positive and negative interactions between drugs?

  Synergism: two antibacterial drugs may be administered together to improve efficiency

  Antagonism: two antimicrobial or between antimicrobials and non-antimicrobial drugs being used to treat other conditions

  Positive: increase efficiency

  Negative: one drug affects another
• Bacterial static def.


  preventing growth
• Bactericidal def:


  killing bacteria
• What is the mode of action for drugs that inhibit the cell wall?

  B-lactam (penicillin) ring prevents the synthesis of peptidoglycan

  • natural: extracted from penicillium cultures, narrow spectrum
  • semisynthetic: contains chemically added side chains, resistant to penicillinase
• What is the mode of action for drugs that inhibit protein syntesis?

  Targets diff. steps in bacterial translation

  • changes shape of 30s portion, causing code on mRNA to be read incorrectly
  • binds to 50s portion & inhibits the formation of the peptide bond (chloramphenicol) suppress the bone marrow, affects blood cell formation
  • interfere w/ attachment of tRNA ribosome complex (tetracyclines) to suppress normal intestinal microbiota
• What mode of action for drugs that inhibit membrane function?

  Change membrane permeability, some drugs create a channel exposing the cell to everything; affects host = skin infection
• What is the mode of action for drugs that inhibit nucleic acids?

  DNA & RNA; interferes w/ replication and transcription

  • variety of ways: block DNA rep. & transcript, inhibit polymerase and helicase, block transcription: inhibit RNA polymerase (no RNA)
• What is the mode of action for drugs that inhibit metabolic pathways?

  Interferes w/ PABA (precursor of nucleotides)

  • antimetabolites compete with normal substrates for an enzyme
  • stops synthesis of folic acids
• Modes of action for fungi?

  • Inhibit synthesis of cell walls
  • disrupt membranes
  • interfere with RNA and DNA synthesis disrupting fungal replication
• Modes of action for protozoa?

  • Inhibition of folate syntesis which is essential for DNA synthesis and cell replication
  • disruption of the electron transport chain, leading to cellular damage and death
  • disruption of microtubule interfering with cell division and leading to cell death
• Modes of action for helminths?

  • Drugs mimic the structure of nucleosides or nucleotides required for viral DNA or RNA synthesis
  • some drugs inhibit essential items for viral proteins to produce
  • some drugs prevent viral entry into host cells by blocking specific viral attachement or fusion proteins, thereby preventing infectio
• What is drug resistance?

  Happens when microbes develop resistance

  • "Superbug" = microbes constantly evolving
  • not overused or misused
  • inappropriate use
  • subtherapeutic dosing
  • patient noncompliance w/ recommended dose
• What is drug modification or inactivation?

  b-lactamase destroys penicillin (ring)
• What is the prevention of cellular uptake?

  inhibition of the accumulation of an antimicrobial drug, prevents antibiotic out of the cell, fights several antibiotics at the same time
• What is target modification?

  structural changes to targets can prevent drug binding, rendering the drug ineffective
• What is target overproduction or enzyme bypass?

  target enzyme overproduces
• What is target mimicry?

  proteins prevent "superbug": microbes constantly evolving
• What are some tests used to determine microbe susceptibility to an antimicrobial drug?

  Immunity genes: resistance genes that exist in nature

  Horizontal gene transfer: transferred immunity
• How do you overcome drug resistance?

  give an appropriate conc.

  • two or more at some time
  • use when necessary
• How can we test the effectiveness of antimicrobials?

  Uses

  • Paper disk w/ a chemotherapeutic agent placed on agar
  • zone of inhibition around the disk determines sensitivity to antibiotic

  -dilution test: places in well trays; E test determines how sensitive bacteria is