Lecture 17, (Maybruck 2) 10/22; Control of Microbial Growth (cont.)

Audio for lecture.

• • Slide 1 (slide labeled number 12 on the handout from 10/17)
• Sterilization with steam under pressure, this is the only way it can get up to 121ºC
• • Slide 2
• pasteurization does not remove endospore forming bacteria
• removes all vegetative forms of bacteria
• juice, beer, wine, milk are all pasteurized
• two methods used to pasteurize
• • flash method –
• • batch method – exposes microorganisms between 63-66º C for a longer exposure time of 30minutes
• two infections
• • salmonelosis – upon ingestion it will coat the lining of the large intestine (large intestine absorbs extra water) and prevents absorption of extra water.
• • brucellosis – mucus covers are GI tract which aids movement of food. It also traps bacteria and brings it to the stomach in order for it to be destroyed. Brucella escapes this mucis and penetrates to the blood vessels and has a grand ol’ time.
• • Slide 3
• Cold has primarily microbistatic effects
• Food inadequately cooked after being thawed may harbor pathogens
• • Slide 4
• Ionizing radiation (loss or gain of electrons)
• • As the wavelengths decrease the energy associated with that wave increases (enough to break chemical bonds)
• • Ionization causes atoms to lose their electrons and causes them to not be bound to one another anymore.
• • Ionizing radiation can be considered a Sterilant as a removal of endospores
• • Types of radiation that are effective as sterilants are: some UV, x-rays, and gamma rays. (they all attack DNA)
• Ionization radiation acts indirectly and forms oxygen radicals which are very reactive. They are always seeking to make chemical bonds.
• Radiation helps to remove contaminants and prolong shelf life.
• • Slide 5
• Sterilization through filtration (used only on liquid or air)
• Bacteria are .2um – 2um
• Protozoa and algae are 2um – 200um
• Create filter with a pore size less than .2um
• Filtration = sterile
• • Slide 1 (handout from 10/22/07)
• Desirable qualities of chemical antimicrobial agents for decontamination in health professions
• • Rapid action at low concentrations
• • Soluble in water or alcohol
• • Destruction of MOs without harm to animal tissue
• • Penetrates surfaces
• • Resistance to inactivation by organic matter
• • Noncorrosive or nonstaining properties
• • Affordable
• • Slide 2 (list found in book)
• High activity – acts as sterilant
• Intermediate activity – acts as disinfectant
• Low activity – acts as disinfectant to an antiseptic.
• • Slide 3
• How to choose an effective chemical antimicrobial agent
• • Look at characteristics – ex. Are they spore formers or not?
• • Characteristics of surface being treated – ex. Is there organic matter that could interfere. Is the surface porous or nonporous.
• • Initial contamination amount
• • Antimicrobial exposure time
• • Strength of antimicrobial chemical
• • Slide 4
• Halogens (group 17) – non-metals that are readily ionized. They love to gain electrons. When they gain that electron they become halides (the ionized state of a halogen). If iodine is ionized it becomes iodide. The non-ionized state is the more effective antimicrobial state.
• Chlorine is an effective antimicrobial agent.
• • When mixed with water it creates hypochlorous acid which reacts with cystine amino acids (breaks up disulfide bridge)
• • Cystine amino acids have a side chain group that contains sulfur. That sulfur will bind with other cystine amino acids. When they bind they form a covalently bonded disulfide bridge.
• Insulin helps cells take up glucose. Glucose is a carbohydrate we use for energy. Break the disulfide bridge, break up the cell.
• Iodine (another example of halogen) interferes in disulfide bridges and hydrogen bonds.
• Act at intermediate activity level
• • Slide 5
• Phenol – 6 carbon sugar - hydroxel group (OH group)
• Phenolic – any molecule that contains one or more phenol groups
• • Bind to proteins and interferes with their function. They make proteins hydrophobic. Hydrophobic – don’t like water.
• Chlorohexidine is rendered useless by toothpaste as it creates a surfactant
• You can adjust disinfectants by altering their concentrations to turn them into antiseptics.
• • Slide 6
• Alcohols – contain hydrocarbon group with one or more hydroxal groups
• Alcohols act as surfactant. Integrate themselves into cell membrane because they have similar characteristics of the phospholipids. Once there they destabilize membrane and allow things in and out of the cell that shouldn’t be ther.
• Alcohols also Denature proteins
• Decontamination characteristics of alcohol will be effective at >50% concentration.
• • Most effective at 70% alcohol and 30% water
• • It needs water to make it effective. If all the water is removed the proteins will remain stable.
• Alcohol is generally considered as a disinfectant. can be used as an antiseptic but can have adverse affects if it is absorbed through the skin.