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Chapter 7 micro
 

Chapter 7 micro

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    Chapter 7 micro Chapter 7 micro Presentation Transcript

    • Chapter 7 The Control of Microbial Growth
    • Control of Microbial Growth
      • Sterilization = the complete removal or killing of all microbes - they are unable to reproduce even in most favorable conditions – no partial sterilization
        • Endospores are one of the most resistant forms of life
          • Their destruction is the goal of sterilization because any process that kills endospores will kill the vegetative cell
        • Used on inanimate objects or material ex. Liquid media
    • Control of Microbial Growth
      • Disinfection = the reduction or removal of vegetative pathogens but not endospores by chemicals, UV radiation, boiling H2O or steam
        • Chemical agents used
          • If object is inanimate (tabletop) = disinfectant
          • If object is living (animal tissue) = antiseptic
            • Antiseptics are regulated by FDA
    • Some definitions
      • Sepsis = Greek for putrid
        • Refers to growth of microbes in blood and other tissues
        • Is stem for septicemia (in blood), antiseptic, aseptic
      • Degerming = mechanical removal (not killing) of microbes from surface of object
        • Ex. ROH w/ shot, wash hands
    • Some definitions
    • Physical Control of Microbes
      • Thermal death point (TDP) = the lowest temp. required to kill all microbes in a liquid culture in 10 minutes
        • For spore bearing organisms there are 2 TDPs – 1 for the vegetative cell and 1 for the spore form
      • Thermal death time (TDT) = length of time to kill all microbes in a liquid culture at a given temperature
      • TDP and TDT are important in the food industry wh/ uses heat for preservation
    • Sterilization by Heat
      • Heat is fast, reliable and cheap and does not introduce toxic substances into material being treated
      • Moist heat
        • Kills microbes by denaturing proteins – breaks H-bonds thus chgs shape
        • Penetrates material faster than dry heat so need less time and lower temperatures
        • Boiling H2O – not a sterilizing agent because of spores and viruses
    • Sterilization by Heat
      • Autoclave (pix –pg 191) = pressure is used to raise temp of steam > 100 Deg. C
        • Most rapid and efficient method of sterilization by heat
        • As pressure > temp. rises
        • At 15 psi pressure the temperature rises from 100 deg C to 121 deg C
        • 15 psi at 121 deg C 15 – 30 min depending on what you are sterilizing
    • Sterilization by Heat
      • Autoclave continued:
        • Used to sterilize culture media, instruments, dressings, glassware, equipment (transfusions)
          • Steam can’t penetrate Al foil – use paper
        • Sterilization check w/ Bacillus spores – incubate to check for growth, tape
      • Pasteurization – destroys Mycobacterium tuberculosis (TB) and Coxiella burnetii (Q fever)
    • Sterilization by Heat
      • Pasteurization continued:
        • Purpose is to reduce bacterial populations of liquid (milk, juice) and to destroy organisms that cause spoilage and human disease without affecting flavor
        • Does not sterilize – spores aren’t affected
        • Methods
          • Classic = heating at 63 deg C 30 min
          • High temp short time tx – 72 deg C 15 sec. – kills pathogens and lowers bacterial counts, >shelf life
    • Sterilization by Heat
      • Pasteurization cont.
        • Ultra – high temp tx
          • – 140 deg. C for 1 sec
          • Holding tube 3 sec.
          • Vacuum chamber 1 sec to cool
          • Can then store milk without refrigerating
            • Actually sterilizes milk
    • Sterilization by Heat
      • Dry heat – Direct flame – incinerates microbes rapidly
        • Bunsen burner – inoculation loop, culture tube – organisms, dust, lint
        • England 4 million cows in 2001 – infected with hoof and mouth disease
        • Used to burn diseased bodies centuries ago
        • Cows and fields exposed to Anthrax (spores)
    • Sterilization by Heat
      • Dry heat – hot air ovens
        • Does not penetrate material easy so needs long periods of time at high temps – 170 deg C at least 2 hrs
        • Used to sterilize dry powders, water free oily substances, glassware
        • Changes microbial proteins by oxidation rxs
    • Filtration
      • Used in food industries, laboratories (medical, environmental, industrial)
      • A filter is a mechanical device used to remove microbes from a solution or gas
      • Several types of filters used in a laboratory
        • Membrane filter – cellulose acetate or polycarbonate – 0.22um, 0.45um, .01um – viruses, lg protein molecules
    • Filtration
      • Membrane filtration cont.
        • Can use to sterilize media or any liquid that can’t tolerate heat
          • Serum, blood products, drugs, IV fluids, enzymes
        • Can use for a bacterial count – traps bacteria on filter which is place on media in a petri dish and incubated
    • Membrane Filtration of Liquids Bacteria removal is easier than removal of viruses. Bacteria removal is not quite equivalent to sterilization.
    • Filtration
      • HEPA filters (high efficiency particulate air) – removes microbes from air
        • Removes 99 % of particles > 0.3um
        • Used in hospitals – whole rooms, labs – hoods, home air filters
    • HEPA Filtration of Air
    • Control of Microbial Growth
      • Low temperatures – refrig, freezer
        • Slows growth but does not kill
        • < enzyme activity, lowers rate of chemical rxs in cytoplasm
      • Desiccation = drying
        • Viruses, endospores resistant
      • Lyophilization = freeze drying
        • Coffee, fruit additives for cereals, used to preserve microbes in laboratory
    • Control of Microbial Growth
      • Osmotic pressure
        • High salt, sugar or spice external environments ( hypertonic environment ) – higher water concentration in cell than outside cell causing H2O to flow from the cytoplasm thru cell membrane out to the environment
        • Causes cell to shrivel and die – cell membrane pulls away from cell wall = plasmolysis
        • Preserves foods – ex. Ham, bacon
    • Radiation
      • Ionizing radiation = high energy radiation that induces electrons to jump out of molecules they strike and create ions = atoms or molecules that lack 1 or more electrons
        • ex. X-rays, gamma rays, high energy electron beams
        • X-rays and gamma rays enter cells and break bonds in DNA causing cell mutations and death
    • Radiation
      • Ionizing radiation cont.
        • Some foods have been irradiated for more than 50 years
          • Radiation is used to kill bacterial pathogens, insects, worms and to inhibit the sprouting of potatoes ( > shelf life of food)
        • Used to sterilize heat sensitive vitamins, hormones, Abs, plastics, suture material
          • Used to sterilize mail after Anthrax scare
          • Used to preserve food
          • Bone, skin and heart valves for grafting - sterilized
    • Radiation
      • Non-ionizing radiation - has a longer wavelength and less energy
        • Ultraviolet Light (UV) – has a wavelength of 100 - 400 nm
          • Used for airborne or surface contamination in hospital rooms, food industry, toilets
          • Bacteria are destroyed at approx. 260 nm – causes thymine dimers (bonds form between adjacent bases on the same DNA strand) – bacteria can no longer produce proteins or reproduce DRAW
        • Disadvantage = does not penetrate liquids or solids
    • Chemical control of Microbes tables pg 207-08
      • Most chemical methods are unreliable for sterilization but are effective as disinfectants and preservatives
      • Evaluating a disinfectant
        • Phenol coefficient test – compare the activity of a disinfectant with that of phenol
        • American official Analytical Chemist’s use – dilution test – current standard
    • Evaluating a Disinfectant
      • Use – dilution test
        • Use Salmonella, Staphylococcus , and Pseudomonas as test microbes
        • A series of tubes containing concentrations of the test disinfectants are inoculated and incubated
        • The more the chemical can be diluted and still be effective the higher its rating
    • Evaluating a Disinfectant
      • Disk-diffusion method – pg 199
        • Filter paper disk is soaked with a chemical and placed on an agar plate that has been inoculated with a test organism and then incubated
        • After incubation if the chemical is effective will see a clear zone of inhibition around the disk
          • Also used to evaluate microbial susceptibility to Abs
    • Types of Disinfectants
      • Phenol and phenolics (phenol derivatives)- disrupt plasma membranes resulting in leakage of cellular contents, denature proteins
      • 1860’s – Joseph Lister established the principles of aseptic surgery by using carbolic acid (phenol ) on wounds and instruments
      • Phenol is caustic to skin and has been replaced by phenol derivatives wh/ are better germicidals and have lower toxicity
    • Types of Disinfectants
      • Phenol derivatives
        • Cresols – derived from coal tar
          • O-phenylphenol used in Lysol, Amphyll
        • Bisphenols = 2 phenol molecules – prominent in modern disinfection
          • Hexachlorophene = pHisoHex – combined with detergent to bath infants to retard Staph infections of scalp and umbilical cord – found could be absorbed through the skin and cause neurological damage – removed from OTC products
    • Types of Disinfectants
      • Bisphenols cont.
        • Triclosan – broad spectrum antimicrobial agent – destroys plasma membrane by blocking lipid synthesis
          • Found in soap
      • Halogens oxidize proteins, disrupts membranes
        • Chlorine – as gas or in combination with other chemicals
          • Germicidal action caused by hypochlorous acid (HOCL) that forms when chlorine is added to H2O
          • Sodium hypochlorite 5% - Clorox bleach , disinfectant in dairies, food processing plants, hemodialysis systems
            • In emergency CDC recommend 2 drops/liter (clear H2O) for 30 min.
          • Chloramines (Cl + ammonia) release free chlorine slower than hypochlorite solution and are more stable
            • Used for disinfectants, antiseptics, sanitizing agents, tx of H2O supplies
    • Types of Disinfectants
      • Iodine – more germicidal than chlorine , found in marine seaweed
        • Tincture of iodine (iodine dissolved in ROH) – used as antiseptic for wounds
        • Iodophors = iodine-detergent complexes that release iodine over a long period of time ex. Betadine – for local wounds
    • Iodine & Iodophores
    • Types of Disinfectants
      • Alcohols – denature proteins and disrupt membranes
      • ETOH and isopropyl ROH are effective in killing vegetative bacteria and fungi but not endospores or nonenveloped viruses
        • Used to disinfect thermometer, medical instruments, mechanically remove bacteria from skin before drawing blood or giving a shot
    • Heavy Metals
      • Hg, Ag, Cu – denatures proteins
      • Small amts of heavy metal (Ag, Cu) have antimicrobial effects = oligodynamic action
        • Demonstrated when place a coin on petri dish w/ bacteria and growth is inhibited from diffusion of metals into media
        • 1% silver nitrate solution used to be placed in eyes of newborns to guard against Neisseria gonorrhoeae
          • Can cause blindness if contracted while going thru birth canal
          • Can cause eye irritation so now use antibiotics
    • Heavy Metals
      • Hg used in the form of mercuric chloride used for skin disease but toxic to skin
        • Mercury compound – thimerosal – vaccines , 1999 CDC advised removal
      • Copper as Cu sulfate is used as an algicide to control algal and cyanobacteria growth in swimming pools, fish tanks, and H2O supplies
      • Zinc chloride used in mouth washes , Zn oxide is used in paints as an anti-fungal
    • Types of Disinfectants
      • Soaps and detergents are surfactants that emulsify particles and reduce surface tension, good degerming agents
      • Aldehydes – denature proteins
        • Formaldehyde
          • Gas at high temps used to sterilize hospital gowns, medical instruments
          • MC as formalin a 37% aqueous solution used to preserve biological specimens, embalming fluid, inactivate bacteria and viruses in vaccines
    • Aldehydes
      • Glutaraldehyde – disinfectant that can be considered as a sterilizing agent
        • Kills bacteria and viruses in 10 min. and spores in 3 -10 hrs
        • Used to sterilize endoscopes, respiratory therapy equipment
        • Also used for embalming