controlling microbial growth - wouguralnl/gural/318microbialcontroli.pdftitle: biology 218...
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Controlling Microbial Growth
• Basic principles• Selection of methods• Physical control
methods• Chemical control
methods• Problems
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Hospital Control
Famous DoctorsSemmelweis (1800)
and Lister (early 1900)
Aseptic methods for surgery, boiled instruments
Disinfectants for hands/wounds
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Nightingale (1800-1900)Sanitary procedures and trainingProcedures for reducing hospital overcrowding
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ContaminationMicrobes present - may or may not be growingInanimate objects - fabrics, food, water…Living objects - hands, animals, bugs…
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Why Control Microbes?Prevent/control diseasesPreserve food and increase shelf-lifeQuality control during production, research
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Modes of Action
Alteration of cell membranes or wallsDamage to proteins or nucleic acids
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Selection of methods• Inexpensive• Fast acting• Stable during storage• Site to be treated• Relative susceptibility:
Factors That Influence Growth
Nutrient and oxygen availabilityTemperature, pH, and pressureMoisture content and salt/sugar
solute levels
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General Strategies to Control GrowthKill or inhibit microbes using chemicals or drugsBlock entry for microbes or carriersPromote people’s natural defenses
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Physical MethodsHeat1. Dry heat or flaming/
burning - many tools, glass2. Boil/steam 5 min kills most
- NOT spores3. Only autoclave - 121°C 20
min - kills ALL4. Pasteurize (60°C, 30 min.)
does NOT = sterilize. 5. Ultrahigh temperatures =
flash heating 140oC for 1-3 seconds
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Miscellaneous Physical MethodsCold/Freezing: slows growth - does not always
killSound waves dislodges - does not kill well
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RadiationUV sterilizes surfaces; X-rays penetrateDestroy DNAIncreasingly applied to mail and foods
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FiltrationFilters made of nylon, porcelain, gauze, sandPlaced in air vents, water valves, masks, etc…Pores/holes 0.45 microns trap most bacteriaPores of 0.20 microns trap most viruses
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Methods
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Osmotic pressure
• Drying & Dessication• Salting/brining• pH
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Chemical Antimicrobials
Ideal ChemicalsEffect happens in a reasonable timeNon-toxic or non-corrosive to materialsWater-soluble, easy to prepare, stable
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Antiseptics for Human Tissues
Detergents disrupt cell membranes—PhenolicsAlcohols, hydrogen peroxide, iodine – disrupt proteins
Antibacterial soaps
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Disinfectants for Non-Living ThingsFormalin destroys DNAPhenol, bleach - proteins
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Gaseous agents
• Ozone• Ethylene oxide
• Use in a chamber: when you cannot use heat or water soluble chemicals
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Arguments Against…Antimicrobial resistanceLoss of “good bacteria” that are protectiveLow immune stimulation, chronic diseases
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Hospital-Acquired Infections
Nosocomial infections on the rise!
2 million patients per 40 million per year
Number of deaths = 75,000-100,000
Added cost = $4.5 billion; stay = 2-4 weeks
Community-acquired –present at admission
Nosocomial – acquired in the hospital setting
Iatrogenic – acquired from health care provide
Reservoirs – people, objects, food/water
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Why?
Indiscriminate use of antimicrobialsDiminished practice of aseptic
proceduresLonger stays - aging, premature
infants, AIDSPatient overcrowding and staff
shortagesPoorly-trained, low-end, temporary
staffGreater use of immune-
suppressantsIndwelling catheters, respirators,
dialysis
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Major Kinds of InfectionsGram Positives – blood, boilsGram Negatives – bladderVarious/both - pneumonia70% agents drug-resistant
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Health Care Workers Also At RiskBlood/fluid – e.g. Hepatitis, AIDSAerosolized respiratory agents - e.g. InfluenzaContact contagious like Staphylococcus30-70% carry resistant Staphylococcus
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Health Care Infection Control Procedures
Medical Asepsis - Clean TechniqueGoals– exclude pathogens, prevent transferHandwashing, handwashing, handwashingProper handling of instruments, fomites, waste
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Standard PrecautionsGoal - reduce transmission of via body fluidsApplied to ALL patients, regardless of statusIncludes medical asepsis plus gloves, masks
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Surgical Asepsis - Sterile TechniqueGoal One – to exclude ALL microorganismsGoal Two - to keep objects and areas sterileEmploys only sterile tools and techniquesUsed during invasive procedures and in all labs
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Hospital Infection Control Committee (ICC)Surveillance, produce reports, educate staffSet policy and take drastic actionCommunicate with local public health Work with hospital clinical microbiology lab