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Presentation on theme: "CONTROL OF MICROBIAL GROWTH"— Presentation transcript:


2 Terminology of Microbial Control
Sepsis/ Asepsis Aseptic techniques Sterilization Commercial Sterilization Sanitization

3 Antisepsis vs Disinfection
Biocide vs Biostatic Degerming Chemotherapy

4 Factors that influence the effectiveness of anti-microbial procedures:
microbial characteristics number of microbes Decimal reduction time (D value) environmental influences time of exposure concentration or intensity of treatment


6 Physical or Mechanical Methods
Heat (moist & dry) Filtration Low temperature High pressure Desiccation & Osmotic pressure Radiation

7 Heat Moist Heat Dry heat Boiling kills most vegetative forms in 10 min
Autoclave – steam under pressure Sterilization - 15 psi, 121OC for 15 min Pasteurization Standard methods do not sterilize higher temp, shorter exposure time Dry heat Incineration Flaming dry heat sterilization Requires higher temp and longer exposure 170°C for 2 hours is equivalent to autoclaving

8 2. Low Temperatures 3. Filtration Slows metabolic rate
Freezing forms ice crystals that can damage cells Slow freezing then thawing does most damage 3. Filtration Mechanical sterilization of heat-sensitive material HEPA filters (high efficiency particulate air filters) Membrane filters have pores as small as 0.01 microns

9 4. High Pressure Up to 130,000 psi Endospores are resistant
Commercially pasteurize foods Preserves flavor, taste, appearance, and nutritional value

10 5. Desiccation Resistance varies by species
can’t reproduce or grow, but may remain viable Osmotic pressure create a hypertonic environment; dehydrates cells Preserved fruits (sugar), cured meat (salt), and pickles (salt)

11 6. Radiation depends on wavelength, intensity and duration
Ionizing vs non-ionizing Sterilization of food products and disposable medical equipment; water treatment

12 Evaluating Anti-microbial Compounds
Phenol coefficient test Use-dilution test Current industry standard

13 Disk-Diffusion Method

14 Types of Anti-microbial Chemicals
Phenol (carbolic acid) Rarely used, irritating qualities and bad odor Penolic compounds more common Disinfect for surfaces (Lysol) and antiseptic (antimicrobial soaps and lotions) Halogens Iodine – antiseptic or disinfectant May be available as a tincture or iodophore Chlorine - disinfectant (water treatment)

15 Alcohols Affect vegetative forms of bacteria, fungi, and enveloped viruses ethanol and isopropanol - degermer (hand sanitizer) and disinfectant 70% solution typically is most effective Heavy metals Silver; mercury; copper antiseptic, algicide, mildew control paints, placed in newborn’s eyes to prevent spread of gonorrhea

16 Surfactants Soap Emulsification; degerming
Least effective of all chemical methods Anionic Detergents Commercial sanitizers Cationic Detergents disinfectant and antiseptic

17 Peroxygens Aldehydes Disinfectants
Ozone – supplements chlorine in water treatment Hydrogen peroxide – good disinfectant not antiseptic Where do the bubbles come from? Aldehydes Disinfectant and preservative Formaldehyde – formalin Irritating and carcinogenic Glutaraldehyde Liquid chemical sterilant

18 Biguanides Ethylene oxide Chlorohexidine most effect class
antiseptic in lotions, soaps and impregnated into surgical meshes and plastics Ethylene oxide Gaseous chemo-sterilizer 4 -18 hours exposure kills all microbes Useful for heat sensitive materials

19 Food preservatives Organic acids – Sodium benzoate, Sorbic acid
Inhibit mold growth in acidic foods Calcium propionate - fungicide used in bread Inhibit mold growth Nitrates- added to many meat products prevents germination and growth of botulism endospores preserves the pleasing red color ????

20 Antibiotics Nisin- added to cheese to inhibit growth of endospore formers Natamycin – antifungal used in food (mostly cheese) Why should medical antibiotics not be used in food preservation?


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