Antibiotics, Chemotherapy and Sterilization basics

  • Chemotherapy is the treatment of disease with chemicals such as antibiotics and antimicrobials
  • A useful antibiotic is active at a high dilution, has selective toxicity, is stable in storage, is soluble and can be retained in the body at an effective concentration.
  • Antibiotics that affect cell wall synthesis are penicillins, carbapenems, monobactams and cephalosporins
  • Antibiotics affecting the cell wall normally are penicillins alone. Penicillins are effective on gram positive, growing bacteria and has a bacteriocidal effect.
  • Antibiotics that inhibit protein synthesis: aminoglycosides, tetracyclines, macrolides and chloramphenicol. These bind to ribosomes and inhibit translation of protein.
  • Tetracyclines attach to the 30s subunit of ribosome and block attachment of tRNA to the A site. Generally broad spectrum.
  • Aminoglycosides such as streptomycin, kanamycin, gentamycin and neomycin attach to the 30s ribosomal subunit and prevent translation, these are highly toxic.
  • Macrolides such as erythromycin and clindamycin attach to 23s subunit of 50s ribosome. Bacteriostatic effect
  • Chloramphenicol binds to the 23s subunit of 50s ribosome and inhibits peptidyl transferase activity. Have a bacteriostatic effect.
  • Bacteria resist drugs by using penicillinase, by modifying the antibiotics, prevent drug uptake or by drug efflux.
  • Bacteria can come resistant to antibiotics via mutation or exchange of DNA
  • Alternatives to antibiotics include probiotics, pre-biotics, essential oils or acidifiers.
  • We sterilize and disinfect things because bacterial growth needs to be controlled in order to prevent infection, prevent food spoilage or to prevent contamination
  • Sterilization is an absolute method of destruction or removal of all life forms, usually microorganisms.
  • Disinfection is the killing or removal of organisms capable of causing infection. Load is reduced to the point where it is no longer a problem.
  • Preservation is a treatment or condition that prevents the growth of microbes.
  • Antiseptic is a mild chemical agent used on skin or living tissues that kills or inhibits microbe growth.
  • Physical agents for sterilization include heat, incineration or radiation
  • Heat can be dry heat or wet heat. Wet heat is better as it coagulates proteins.
  • Pasteurization is common for milk products and kills most pathogens but not spores, includes LTH, HTST or UHT.
  • Tyndallization is a 3 day cycle of steaming at 100 degrees for 20 mins and is used to treat soils. This is done so that spores that germinate overnight are subsequently killed the next day.
  • Autoclaves use moist heat at high temps and high pressure to sterilize. This is routinely used to sterilize media and objects in a lab.
  • UV radiation is lethal at 260nm and cause thymine dimers however cannot penetrate glass, plastic or paper.
  • Ionizing radiation by gamma rays from Co60 is used to sterilize plastics, petri dishes, gloves and antibiotics.
  • Disinfectants and antiseptics include: soap, alcohol, aldehydes, chlorohexidine, ethylene oxide, halogens, chlorine, iodine and bleach.
  • Resistance to inactivation from most to least: prions, spores, small viruses, gram –ve bacteria, fungi, large viruses, gram +ve bacteria, enveloped viruses.

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