controlling microbial growthwou.edu/~guralnl/gural/318microbialcontroli.pdfphysical methods heat 1....
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Controlling Microbial Growth
• Basic principles• Selection of methods• Physical control
methods• Chemical control
methods• Problems
Hospital Control
Famous DoctorsSemmelweis (1800)
and Lister (early 1900)
Aseptic methods for surgery, boiled instruments
Disinfectants for hands/wounds
Nightingale (1800-1900)Sanitary procedures and trainingProcedures for reducing hospital overcrowding
ContaminationMicrobes present - may or may not be growingInanimate objects - fabrics, food, water…Living objects - hands, animals, bugs…
Why Control Microbes?Prevent/control diseasesPreserve food and increase shelf-lifeQuality control during production, research
Modes of Action
Alteration of cell membranes or wallsDamage to proteins or nucleic acids
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
General Strategies to Control GrowthKill or inhibit microbes using chemicals or drugsBlock entry for microbes or carriersPromote people’s natural defenses
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
Miscellaneous Physical MethodsCold/Freezing: slows growth - does not always
killSound waves dislodges - does not kill well
RadiationUV sterilizes surfaces; X-rays penetrateDestroy DNAIncreasingly applied to mail and foods
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
Methods
Osmotic pressure
• Drying & Dessication• Salting/brining• pH
Chemical Antimicrobials
Ideal ChemicalsEffect happens in a reasonable timeNon-toxic or non-corrosive to materialsWater-soluble, easy to prepare, stable
Antiseptics for Human Tissues
Detergents disrupt cell membranes—PhenolicsAlcohols, hydrogen peroxide, iodine – disrupt proteins
Antibacterial soaps
Disinfectants for Non-Living ThingsFormalin destroys DNAPhenol, bleach - proteins
Gaseous agents
• Ozone• Ethylene oxide
• Use in a chamber: when you cannot use heat or water soluble chemicals
Arguments Against…Antimicrobial resistanceLoss of “good bacteria” that are protectiveLow immune stimulation, chronic diseases
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
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
Major Kinds of InfectionsGram Positives – blood, boilsGram Negatives – bladderVarious/both - pneumonia70% agents drug-resistant
Health Care Workers Also At RiskBlood/fluid – e.g. Hepatitis, AIDSAerosolized respiratory agents - e.g. InfluenzaContact contagious like Staphylococcus30-70% carry resistant Staphylococcus
Health Care Infection Control Procedures
Medical Asepsis - Clean TechniqueGoals– exclude pathogens, prevent transferHandwashing, handwashing, handwashingProper handling of instruments, fomites, waste
Standard PrecautionsGoal - reduce transmission of via body fluidsApplied to ALL patients, regardless of statusIncludes medical asepsis plus gloves, masks
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
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