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Describe three types of microbes that are extremely resistant to antimicrobial treatment, and explain why.
1. Bacterial endospores - most resistant form of life, can survive more than 20 yrs in 70% alcohol
2. Mycobacterium - contains a waxy cell wall (mycolic acid) helps survive the drying & protects from chemicals
3. Cysts of Protozoa - protozoa cysts wall prevents entry of disinfectants, protects against drying & heat.
Compare and contrast four tests that have been developed to measure the efficacy of disinfectants.
Phenol coefficient - Oldest method/efficiency against phenol; the greater the ratio the better
Kelsey-Sykes capacity - Use in Europe/bacterial suspension added to chemical, lack of turbidity is lack of bacterial growth
In-use - Checks real life situations/swab from a suspected site to media and check for growth, most realistic to determining efficacy of chemical
Use - Use in US/Dip metal cylinders into broth culture of bacteria & dry 36 degree C
Why is it necessary to use strong disinfectants in areas exposed to tuberculosis patients?
Because tuberculosis cell wall has lots of waxy lipids mycolic acid, which allows bacteria to survive drying & protects it from most water-based chemical.
Why do warm disinfectant chemicals generally work better than cool ones?
Better penetration with heat.
Why are Gram-negative bacteria more susceptible to heat than Gram-positive bacteria?
Gram (+) bacteria has a thicker peptidoglycan layer than gram (-) & gram (-) has an outer membrane of LPS which contains lipid A
Describe 5 physical methods of microbial control.
Moist Heat - use to disinfect, sanitize, sterilize & pasteurize, kills cells by denaturing protein & destroying cytoplasmic membrane (disinfecting baby bottles)
Dry heat - Used w/ powders, oils & metals. Hot air is used to denature protein & foster oxidation of metabolic & structural chemical.
Refrigeration & Freezing - Used in food preparation & storage. Halts growth of most pathogens, because chemical reactions occur slower at lower temperatures.
Ionizing radiation - denatures molecules DNA, which causes cell death & mutations
Osmotic pressure - high concentration of salt & sugar. Used to preserve food like salted fish.
Desiccation & Lyophilzations - technique combining freezing & drying
What is the difference between thermal death point and thermal death time?
Thermal death point is the lowest temperature that kills all cells in broth in 10 min
Thermal death time is the time that it takes to sterilize volume of liquid at a set temperature.
Defend the following statement: "Pasteurization is not sterilization."
Pasteurization allows thermophilic & thermoduric bacteria to survive (not pathogenic) & sterilization kills all microbes
Compare and contrast desiccation and lyophilization.
Desiccation - Inhibits growth by removing water that microbes need to metabolize
Lyophilization - Uses freezing and drying to preserve microbes for many years, this is long term preservation of microbial culture.
Compare and contrast the action of alcohols, halogens, and oxidizing agents in controlling microbial growth.
Alcohol - denatures proteins & disrupts cell membrane (ETOH)
Halogens - denatures proteins including enzymes (Cl & iodine)
Oxidizing agents - denatures proteins by oxidation (hydrogen peroxide & peracetic acid)
Hyperthemophilic prokaryotes may remain viable in canned goods after commercial sterilization. Why is this situation not dangerous to consumers?
Because hyperthermophilic microbes grow at 85 degree C and not at 37 degree C where we store our food.
Why are alcohols now more effective in a 70% solution than in a 100% solution?
100% alcohol will dry bacteria and not kill it
Contrast the structures and actions of soaps and quats.
They are both detergents. SOAPS do not kill organism, they are washed off surfaces & QUATS disrupt cellular membrane where the affected cell lose internal ions
What are some advantages and disadvantages to using ionizing radiation to sterilize food?
Advantages - kills microbes, larvae & eggs; also kill cells that spoil or over ripen fruits & vegetables
Disadvantages - Can be cancer causing & change taste & nutritional value of fruit & vegtables
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