MICRO

• Antimicrobial chemotherapy


  The use of drugs to control infection on or in the body
• Antimicrobial drugs


  Produced either synthetically or from natural sources
• Broad-spectrum antimicrobials


  Effective against many types of microbes
• Narrow-spectrum antimicrobials


  Effective against a limited group of microbes
• Considerations to choose an effective antimicrobial


  • The nature of the infecting microbe
  • The microbe's sensitivity to available drugs
  • The overall medical status of the infected host
• Kirby-Bauer test


  Identifies antimicrobials that are effective against a specific infectious bacterial isolate
• There are a great number of antibacterial drugs, but a limited number that are effective against protozoa, helminthes, fungi, and viruses
• Cellular targets for antibiotics in microbes


  • Cell wall synthesis
  • Nucleic acid structure and function
  • Protein synthesis
  • Cell membranes
  • Folic acid synthesis
• Drugs that block cell wall synthesis


  • Penicillins
  • Cephalosporins
  • Carbapenems
  • Vancomycin
• Drugs that block protein synthesis


  • Aminoglycosides
  • Tetracyclines
  • Erythromycin
  • Ketolides
• Synthetic antimicrobials that block nucleic acid synthesis


  • Sulfonamides
  • Trimethoprim
  • Fluoroquinolones
• Drugs that disrupt cell membranes


  • Polymyxins
  • Daptomycin
• Bacteria in biofilms respond differently to antibiotics than when they are free-floating
• It is therefore difficult to eradicate biofilms in the human body
• Fungal antimicrobials


  • Macrolide polyenes
  • Azoles
  • Echinocandins
  • Flucytosine
• There are fewer antiprotozoal drugs than antibacterial drugs because protozoa are eukaryotes like their human hosts; they have several life stages, some of which can be resistant to the drug
• Antihelminthic drugs immobilize or disintegrate infesting helminthes or inhibit their metabolism in some manner
• Mechanisms of action for antiviral drugs


  • Blocking viral entry into cells
  • Blocking the replication process
  • Preventing the assembly of viral subunits into complete virions
• Drug resistance


  Microorganisms are no longer inhibited by an antimicrobial to which they were previously sensitive
• Mechanisms of microbial drug resistance


  • Drug inactivation
  • Decreased drug uptake
  • Decreased drug receptor sites
  • Modification of metabolic pathways formerly attacked by the drug
• Widespread indiscriminate use of antimicrobials has resulted in an explosion of microorganisms resistant to all common drugs
• Research strategies for new antibiotics


  • Targeting iron scavenging pathways of microbes
  • Use of RNA interference
  • Mimicking natural defense peptides
  • Use of bacteriophages
• New targets for antiviral therapy may focus on host factors that the virus needs for its reproduction
• Probiotics and prebiotics


  Methods of crowding out pathogenic bacteria and providing a favorable environment for the growth of beneficial bacteria
• Major side effects of antimicrobials


  • Toxicity to organs
  • Allergic reactions
  • Problems resulting from alteration of normal biota
• Antimicrobials that destroy most but not all normal biota can allow the unaffected normal biota to overgrow, causing a superinfection
• Chemotherapeutic drug


  A drug treatment that uses powerful chemicals to kill fast-growing cells in your body
• Antimicrobial


  Any antimicrobial drug, regardless of its origin. An antimicrobial is an agent that kills microorganisms and stops their growth
• Antibiotic


  Substances produced by the natural metabolic processes of some microorganisms that can inhibit or destroy other microorganisms; generally. The term used for targeting bacteria and not other types of microbes
• Antiviral


  Targets specific points in the infectious life cycle of viruses
• Antifungal


  Antifungals are used to treat fungal infections. Cells of fungi are eukaryotic, therefore the majority of antimicrobial drugs designed to attack bacteria and are generally ineffective in combating fungal infections. Also, drugs toxic to fungal cells are also capable of harming human tissues
• Antifungal drugs


  • Macrolide polyenes
  • Azoles
  • Echinocandins
  • Allylamines
• Antiprotozoal


  Kills or inhibits growth of protozoans
• Synthetic drugs


  Drugs produced entirely by chemical reactions
• Semi-synthetic drugs


  Drugs that are chemically modified in the laboratory after being isolated from natural sources
• Broad-spectrum


  Antimicrobials effective against a wide variety of microbial types-for example, a drug effective against both gram-positive and gram-negative bacteria
• Narrow-spectrum


  Antimicrobials effective against a limited array of microbial types-for example, a drug effective mainly against gram-positive bacteria
• Drug resistance


  The reduction of effectiveness of a drug or medication in treating a disease or condition
• Therapeutic index (TI)


  The ratio of the dose of the drug that is toxic to humans compared to its minimum effective (therapeutic) dose. The closer these two figures are (the smaller the ratio), the greater the potential for toxic drug reaction
• It is best to choose the one with high selective toxicity for the infectious agent and low human toxicity