Micro

• The methods of microbial control used outside of the body are designed to result in 4 possible outcomes 


  sanitization, disinfection, antisepsis, and sterilization
• sanitization

  Sanitizing kills bacteria on surfaces using chemicals, it is not intended to neutralize viruses
• Disinfection

  Disinfecting neutralizes viruses and kills bacteria on surfaces using chemicals(does not kill bacterial endospores)
• asepsis

  Any practice that prevents the entry of infectious agents into sterile tissues and thus preventsinfection
• sterilization


  Process that destroys or removes all viable microorganisms (including viruses and endospores)
• Bacterial endospores havetraditionally been considered themost resistant microbial entities


  The goal of sterilization is thedestruction of bacterial endospores
• Bacteristatic


  chemical agents that prevent the growth ofbacteria on tissues or on objects in the environment
• Fungistatic


  chemicals that inhibit fungal growth
• Bactericidal


  destroys bacteria except for those in theendospore stage
• Fungicidal:


  kills fungal spores, hyphae, yeasts
• Virucidal


  inactivates viruses, especially on living tissue
• Sporicidal


  destroys bacterial endospores (achieves sterility)
• Mechanical, Filtration 


  Pore sizes can be controlled to permit truesterilization by trapping viruses or large proteins• Pore size 0.2 μm (micron) filters out mostbacteria• Pore size 0.02 μm filters out most viruses
• Filtration is important to water purification 


  unable to remove toxins
• physical, heat

  Lower temperatures are microbistatic (slows activities- enzymes or metabolic reactions), Elevated temperatures are microbicidal(moist or dry)
• Moist heat- water+heat 


  boiling water- disinfection not sterilize (does not kill endospores)

  pasteurization- disinfection not sterilize

  autoclaving- steam under pressure ( WILL STERILIZE)
• Dry heat-killing microbes using heat- no water involved 


  IncinerationDirect exposure of bacteria to intense heat (several thousand °C),burns microbes to ashes and gases

  Hot air oven-sterilization needs 3 hours, destroys endospores
• Moist vs dry heat

  Moist heat:Operates at lower temperatures and shorter exposuretimes to achieve the same effectiveness as dry heatMicrobicidal effect is the coagulation (clotting) anddenaturation of proteins

  Dry heat:Dehydrates the cell, removing waternecessary for metabolic reactionsAt very high temperatures, oxidizes cells,burning them to ashes and gases
• Physical- ultraviolet radiation 


  Causes damage to cells through two main pathways:• formation of thymine dimers in DNA and• generation of reactive oxygen species

  Disadvantages• UV does not penetrate glass, plastic or water very well• Not good for surfaces with lots of “hiding places”

  DOES STERILIZE
• prevention of uv related damage

  1. DNA repair enzymes e.g. Photolyase2. Antioxidant enzymes e.g. superoxide dismutase,catalase3. Pigments e.g. carotenoids, melanin• ROS scavenging• Dissipation of excitation energy as heat4. Negative phototaxis – navigate away from light
• Ionizing Radiation 


  Causes double strand DNA breaks
• Chemical control- alcohol 


  Work by denaturing proteins and disrupting cell walls & membranes

  Effective against vegetative cells
• Chemical control-Halogens 


  They generally disrupt microbial enzyme function

  Effective against vegetative cells and some endospores
• Chemical Control- Oxidizing Agents 


  Work by oxidizing enzymes thus shutting down the microbe’s metabolism

  Bactericidal, virucidal, and fungicidal; sporicidal in higher concentrationsEspecially effective against anaerobic organisms
• Chemical Control- Phenol 


  They denature proteins and disrupt cell membranes

  Effective against vegetative cells but not spores
• Chemical control - Surfactants


  Work by disrupting the cell membrane structure

  Generally, work well against vegetative cells but not endospores
• Chemical control - Heavy Metals

  Bind to proteins, inhibit enzymatic activity

  work well against vegetative cells but not endospores
• Chemical control - Aldehydes


  Work by: denaturing proteins inactivating nucleic acids inactivating membranes

  Effective at sterilization
• Biological Control of Microorganisms

  emerging field that shows great promise- natural control
• selective toxicity 


  kill or inhibit microbial cells without damaging host tissues
• Drugs with excellent selective toxicity block the synthesis of the bacterial cell wall(penicillins and cephalosporins)


  Human cells lack the chemical peptidoglycan and are unaffected by the drug
• Antibiotics are natural metabolic products of bacteria and fungi


  Produced to inhibit the growth of competing microbes inthe same habitat (antagonism)
• Goals of chemotherapy: disrupt the structure or function of an organism to thepoint where it can no longer survive


  Antimicrobial drug categories:• Inhibition of cell wall synthesis• Inhibition of nucleic acid structure and function• Inhibition of protein synthesis• Interference with cytoplasmic membrane structure and function• Inhibition of folic acid synthesis
• Drugs That Target the Cell Wall

  Most drugs that target the cell wall contain a beta-lactam ring in their molecular structureβ-lactams inhibit the synthesis of the peptidoglycan layer of bacterial cell wallsEspecially useful against Gram positive organisms
• Penicillin resistant bacteria


  Microbes resistant to penicillin have β-lactamase or penicillinase which hydrolyzes the β-lactam ring and inactivates its antibacterial properties

  Some bacteria, e.g. E. coli, produce an enzyme called extended spectrum beta-lactamase(ESBL), this enzyme makes ESBL bacteria harder to treat with antibiotics

  Methicillin-resistant Staphylococcus aureus (MRSA) are resistant to all beta-lactamantibiotics including penicillins and cephalosporins
• Drugs That Target Protein Synthesis

  Aminoglycosides: stick to ribosomes and causethe misreading of the mRNA, leading to abnormalproteins

  Tetracyclines: block the attachment of tRNA onribosomes and stop further protein synthesis

  Macrolides: stick to ribosomes inhibit movement oftRNAs during protein synthesis
• Drugs That Target Folic Acid Synthesis, DNA or RNA

  Sulfonamides (sulfa): interfere with folate metabolism by blocking enzymesrequired for the synthesis of tetrahydrofolate (B9), which is needed by the cells forfolic acid synthesis and eventual production of DNA, RNA, and amino acids
• Drugs That Target Cytoplasmic or Cell Membranes

  Polymyxins (colistins): interact with membranephospholipids; distort the cell surface and cause leakageof protein and nitrogen bases, particularly in gram-negative bacteria
• Spectrum of Activity

  Broad-spectrum drugs: effective against more than one group of bacteria

  Narrow-spectrum drugs: target a specific group
• Bacteria in Biofilms

  Bacteria in biofilms are often unaffected by antimicrobials, Antibiotics often cannot penetrate the sticky extracellularmaterial surrounding biofilms Different gene expressionprofiles during free-livingvs. biofilm stages