Transcript CHAPTER 5
CHAPTER 7 CONTROL OF MICROBIAL GROWTH Terminology of Microbial Control • Sepsis • Asepsis – Aseptic techniques • Sterilization • Commercial Sterilization • Sanitization • Antisepsis vs Disinfection – Biocide – Biostatic • Degerming • Chemotherapy Factors that influence the effectiveness of antimicrobial procedures: 1. microbial characteristics 2. number of microbes – Decimal reduction time (D value) 3. environmental influences 4. time of exposure 5. concentration or intensity of treatment Physical or Mechanical Methods 1. 2. 3. 4. 5. 6. Heat (moist & dry) Filtration Low temperature High pressure Desiccation & Osmotic pressure Radiation 1. Heat • Moist 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 2. Low Temperatures – – – 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 4. High Pressure – – – – Up to 130,000 psi Endospores are resistant Commercially pasteurize foods Used to sterilize liquid food products while preserving flavor, taste, appearance, and nutritional value 5. Desiccation – Resistance varies by species • can’t reproduce or grow, but may remain viable – lyophilization • Freeze-drying – freeze then dry in a vacuum Osmotic pressure – – create a hypertonic environment; dehydrates cells Preserved fruits (sugar), cured meat (salt), and pickles (salt) 6. Radiation • depends on wavelength, intensity and duration • Ionizing vs non-ionizing • Sterilization of food products and disposable medical equipment; water treatment Evaluating Anti-microbial Compounds • Phenol coefficient test • Use-dilution test – Current industry standard Disk-Diffusion Method Types of Anti-microbial Chemicals – Phenol (carbolic acid) • Rarely used, irritating qualities and bad odor – Penolic compounds • 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) – 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 – Surfactants • Soap – Emulsification; degerming – Least effective of all chemical methods • Anionic Detergents – Commercial sanitizers • Cationic Detergents – disinfectant and antiseptic – Quaternary ammonium compounds (Quats) – most widely used cationic detergents » Pseudomonas resistant – Peroxygens • 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 – Biguanides • 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 – Food preservatives • Organic acids – Sodium benzoate, Sorbic acid – Prevent molds from growing in acidic foods • Calcium propionate - fungicide used in bread – Inhibit mold growth by interfering with plasma membrane • Nitrates- added to many meat products – prevents germination and growth of botulism endospores – preserves the pleasing red color – 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?