Chapter 7: Control Of Microbial Growth-2 PDF
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This document provides an overview of strategies for microbial control. It details various methods, including heat treatment, filtration, and chemical disinfection, suitable for controlling different types of microorganisms.
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Chapter- 7: Control of Microbial Growth-2 EX PEC TED LEA RN ING O UTC O M E- 2▪ C o m p a r e a n d c o n tr a s t pasteurization, sterilization u s i n g p r e s s u r i z e d s t e a m , a n d the c o m m e r ci al c a n n i n g p r o c e s s. ▪ Explain the d r a w b a c k s a n...
Chapter- 7: Control of Microbial Growth-2 EX PEC TED LEA RN ING O UTC O M E- 2▪ C o m p a r e a n d c o n tr a s t pasteurization, sterilization u s i n g p r e s s u r i z e d s t e a m , a n d the c o m m e r ci al c a n n i n g p r o c e s s. ▪ Explain the d r a w b a c k s a n d benefi ts of u s i n g d r y h e a t rather t h a n m o i s t h e a t to kill m i c r o o r g a n i s m s. ▪ D e s c r i b e h o w d e p t h fi lters, m e m b r a n e fi lters, a n d H E PA fi lters are u s e d to remove microorganisms. ▪ C o m p a r e a n d c o n tr a s t the u s e of g a m m a radiation, ultraviolet radiation, a n d m i c r o w a v e s for d e s t r o y i n g microorganisms. 1 - U s i n g h e a t to destroy microorganisms and viruses H e a t t r e a t m e n t u s e f u l for microbial control Reliable, safe, relatively fast, inexpensive, non-toxic Can be used to sterilize or disinfect 3 1-1-Moist irreversibly denatures heat: proteins Boiling destroys most microorganisms and viruses Does not sterilize: endospores can survive 1-1-A-Pasteurization destroys heat-sensitive pathogens, spoilage organisms 1. High-temperature–short-time (HTST): most products Milk: 72°C for 15 s; ice cream: 82°C for 20 s 2. Ultra-high-temperature (UHT): shelf-stable boxed juice and milk; known as “ultra- pasteurization” 4 Milk: 140°C for a few seconds, then rapidly 1-1-B-Sterilization Using Pressurized Steam Autoclave used to sterilize using pressurized steam Increased pressure raises temperature; kills endospores Sterilization typically at 121°C and 15 psi in 15 minutes (Longer for larger volumes) 5 1-2-Dry heat: Less effective than moist heat; longer times, higher temperatures necessary 200°C for 90 minutes vs. 121°C for 15 minutes Hot air ovens oxidize cell components, denature proteins Used for glass, powders, oils, dry materials Incineration a method of dry heat sterilization Oxidizes cell to ashes Used to destroy medical waste and animal carcasses Laboratory inoculation loop sterilized by flaming 6 2 - U s i n g p h y s i c a l m e t h o d s to r e m o v e or d e s t r o y microbes 2-1-Filtration retaining bacteria 2-1-A-Filtration of fluids Depth filters Membrane Thick porous filters Small filtration material (e.g., cellulose) pore size (0.2 Larger pores µm) to Electrical charges remove trap bacteria 7 Thin cells 2-1-B-Filtration of air: High-Efficiency Particulate Air (HEPA) filters remove nearly all microbes from air 8 2-2-Radiation Electromagnetic radiation: radio waves, microwaves, visible and ultraviolet light, X rays, and gamma rays Energy travels in waves; no mass Wavelength inversely proportional to frequency High frequency has more energy than low frequency 9 Radiation (continued…) Exampl Ionizing radiation can e remove electrons from atoms (e.g. Gamma rays and X rays) Destroys DNA, damages cytoplasmic membranes, reacts with O2 to produce reactive oxygen species 1 Radiation (continued…) M i c r o w a v e s kill by generated heat, not Denatures directly proteins and damages D N A Microwave ovens heat food unevenly, so cells can survive 1 maintai it 2-3-High Pressure ns origin al s Used in cold freshness pasteurization of t h r o u g h o u t th e commercial foods shelf-life For example, guacamole Avoids problems with high temperature pasteurization Employs high pressure up to 130,000 psi Destroys microbes by denaturing proteins and altering cell permeability Products maintain color, flavor associated with fresh food 1 1 3 - U s i n g c h e m i c a l s to destroy Potencymofi c roorganisms and Germicidal viruses Formulations Chemical Low-level di s i nf e c t a nt s destroy fungi, vegetative/ S t e r i l a n t s destroy normal bacteria except all microorganisms mycobacteria, and enveloped Heat-sensitive viruses critical instruments D o not kill endospores, non- enveloped viruses Disinfect furniture, floors, walls Intermediate-level d i s i nf e c t a nt s destroy High-level di s i nf e c t a nt s vegetative bacteria, destroy viruses, vegetative cells mycobacteria, fungi, and most D o not reliably kill viruses endospores Semi-critical D o not kill endospores at instruments any conc. Kill everything but we instrumen Disinfect non-critical 1 cannot relay in it to kill Selecting the Appropriate G er m ici d a Clh e m ica l? ? ? ? ??? 1. Toxicity: benefits must be weighed against risk of use 2. Activity in presence of organic material; many germicides inactivated 3. Compatibility with material being treated (e.g. Liquids cannot be used on electrical equipment) 4. Residues: can be toxic or corrosive 5. Cost and availability 6. Storage and stability; concentrated stock decreases storage space 7. Environmental risk; some agent may need to be neutralized before disposal 1 Think of examples in your daily life of a chemical used a s a disinfectant Agent Characteristic Uses s Alcohols Aldehydes Biguanides Ethylene oxide Halogens Metal Ozone Peroxygens Phenolic Compounds Quaternary Ammonium Compounds 1- Alcohols Kills vegetative bacteria and fungi (low level) Not reliable against endospores, s o m e naked viruses D a m a g e to lipid membranes Commonly used a s antiseptic (on living tissue) and disinfectant Limitations Evaporates quickly, limiting contact time Can d a m a g e rubber, s o m e plastics, and others 1 Examine the table and answer the following questions: 1. What concentration of alcohol is generally effective as disinfectant against S. pyrogenes? 2. W h y do you think 1 0 0 % is not eff ective? 2- AlGlutaraldehyde, dehydes formaldehyde, and ortho-phthalaldehyde (OPA) Inactivates proteins and nucleic acids 2 % alkaline glutaraldehyde c o m m o n s t erilant Immersion for 1 0 – 1 2 hours kills all microbial life Toxic Formaldehyde used a s g a s or a s formalin ( 3 7 % solution) Effective germicide that kills most For use microbes quickly in cattle farms Used to kill bacteria and inactivate viruses for vaccines 2 Used to preserve specimens 3- BExtensive iguanid e sas use antiseptics Stays on skin, mucous membranes Relatively low toxicity Destroys vegetative bacteria, fungi, som e enveloped viruses C o m m o n in m a ny products: skin cream, mouthwash 2 4-Ethylene o x iUseful de g a s eo u s sterilant Destroys microbes including endospores and viruses Reacts with proteins Penetrates fabrics, equipment, implantable devices Pacemakers, artificial hips Useful in sterilizing heat- or moisture-sensitive items M a n y disposable laboratory items Petri dishes, pipettes Applied in special chamber resembling autoclave Limitations: toxic (must be extensively aired), mutagenic and potentially carcinogenic 2 5-Halogens (a group in the periodic table consisting of five chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At)): oxidize proteins, cellular components Chlorine: Destroys all microorganisms and viruses Used as disinfectant Caustic to skin and mucous membranes 1:100 dilution of household bleach effective Very low levels disinfect drinking water Organic compounds interfere 2 C L A S S E S OF GERMICIDAL CHEMICALS Iodine: Kills vegetative cells, unreliable on endospores (Antiseptic) Pseudomonas species can survive in stock solution 2 6-Metal Compounds Combine with sulfhydryl groups ( — S H ) of proteins High concentrations too toxic to be used medically S i l v e r still used a s a n antiseptic: creams, b a nd a g es Silver nitrate eye drops given at birth to prevent Neisseria gonorrhoeae infections Replaced b y antibiotics Co m p o und s of mercury , tin, copper , and others once widely used a s preservatives In industrial products and to prevent microbial growth in recirculating cooling water Extensive use led to environmental pollution No w strictly regulated 2 7-Ozone ( O 3 ) Unstable form of oxygen Decomposes quickly, so generated on-site Powerful oxidizing agent Used as alternative to chlorine Disinfectant for drinking 2 8 - P e r o x y g e n s : powerful oxidizers used a s sterilants Readily biodegradable, no residue Less toxic than ethylene oxide, glutaraldehyde H y d r o g e n peroxide (H 2 O 2 ): eff ectiveness depends on surface Aerobic cells produce enzyme catalase: Breaks down H 2 O 2 to O 2 , H 2 O Doesn’t d a ma ge most materials Hot solutions used in food industry Vapor-phase can be used a s sterilant Peracetic acid: more potent than H 2 O 2 Effective on organic material 2 It is used widely in medicated soaps. 9-Phenolic C o m p o u n d s (P hen ol i cs ) Phenol one of earliest disinfectants Ha s unpleasant odor, irritates skin Phenolics kill most vegetative bacteria Mycobacterium at high concentrations Not reliable on all virus groups Destroy cytoplasmic membranes, denature proteins Leave antimicrobial residue Considered non-toxic for skin applications, use cautioned by FDA and EPA 2 10- Q u a t e r n a r y A m m o n i u m Compounds (Quats) Cationic detergents Low toxicity, disinfection of food preparation surfaces Charged hydrophilic and uncharged hydrophobic regions Reduces surface tension of liquids Aids in removal of dirt, organic matter, organisms Most household soaps, detergents are anionic Positive charges of quats attracted to negative charges of cell surface Reacts with membrane Destroys vegetative bacteria and enveloped viruses Not effective on endospores, mycobacteria, non-enveloped viruses Pseudomonas resists, can grow in solutions 3 3 4 - P R E S E R VAT I O N O F PERISHABLE PRODUCTS 4-1-Low-Temperature Storage Refrigeration inhibits growth of pathogens and spoilage organisms by slowing or stopping enzyme reactions Psychrotrophs, psychrophilic organisms can still grow Freezing preserves by stopping all microbial growth S o m e microbial cells killed by ice crystal formation, but m a n y survive and 3 4-2-Reducing Available Water Drying often supplemented Accomplished by salting, by salting Lyophilization (freeze drying) adding sugar, or drying food foods Coffee, milk, meats, fruits, Addition of salt, sugar vegetables increases environmental Drying stops microbial growth but does not reliably kill solutes Numerous cases of salmonellosis from dried Causes cellular eggs plasmolysis (water exits bacterial cells) S o m e bacteria grow in high salt environments Staphylococcus aureus 4-3-Chemical preservatives Food preservatives must be non-toxic for safe ingestion W e a k o r g a n i c a c i d s (benzoic, sorbic, propionic) Alter cell membrane function Control molds and bacteria in foods N i t r a t e a n d nitrite used in processed atsm e Inhibit endospore germination and ative veget growth cell Stops growth of Clostridium botulinum Higher concentrations give meats pink color Show n to be carcinogenic—form nitrosamines