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11 Controlling Microbes Not Too Hot to Handle
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Physical Methods of Control
Fire is a great sterilizing agent Heat alone, though cannot inactivate spores Radiation is a great sterilizing agent Deinococcus radiodurans resist high levels of radiation, too, though!
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Physical Methods of Control
Heat methods Denature and inactivate proteins Drive off necessary water 100 °C steam from boiling water (moist heat) Cannot inactivate spores Pressure Autoclave 15 psi Allows higher water and steam temperatures 121 °C steam now capable of inactivating spores Figure 11.2: Operation of an autoclave
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Physical Methods of Control
Heat methods Pasteurization 62.9 °C for 30 minutes (hold method) 71.6 °C for 15 to 30 seconds (flash method) 82 °C for 3 seconds (ultraflash method) Used to kill pathogens in milk, wine, fruit juice Does not inactivate spores Protects against Mycobacterium tuberculosis, Coxiella burnetii Dry heat 160 to 170 °C for at least 2 hours Oxidation of proteins Necessary for materials that cannot be autoclaved or pasteurized
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Physical Methods of Control: Heat
Figure 11.3: Temperature and the physical control of microbes
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Physical Methods of Control
Radiation Ultraviolet radiation Results in mutations Effective against spores, since no repair mechanism Ionizing radiation X rays Gamma rays About 10,000 times more energetic than UV light Sterilizing Electron beams Room temperature treatment Can pass through packaging to sterilize contents
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Physical Methods of Control
Drying Also known as desiccation Water required for microbes to survive Removal prevents many enzymatic processes Not effective to inactivate spores Effective for storage of Cereals Grains Other foodstuffs normally stored in pantries
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Physical Methods of Control
Filtration and refrigeration Filtration Heat-sensitive solution passed through filter Pores in filter prevent passage of microbes Pores can be chosen based on size of microbe 0.2 mm to 0.5 mm pores prevent passage of many bacteria Does not prevent passage of viruses Solution is not truly sterilized Refrigeration Slows down enzymatic reactions Only slows microbial growth Refrigerated foods are not sterile
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Chemical Methods of Control
Disinfection and antisepsis Practiced for thousands of years Medicinal chemistry started in the 1800s 1860s: Joseph Lister Principles of antisepsis in surgery Diminished incidence of common infections that occurred during surgery Collection of the University of Michigan Health System, Gift of Pfizer, Inc. Figure 11.6: Joseph Lister
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Chemical Methods of Control
General principles Disinfectants Kill microbes on inanimate objects Antiseptics Kill microbes on body surfaces Ideal agent Soluble in water Kills all microbes Stable over time Nontoxic to humans and animals Uniform composition Combine with organic matter other than microbes Highest efficacy at room or body temperature Efficiently penetrate surfaces Not corrode or rust metals Not damage or stain fabrics Readily available in useful quantities Reasonably priced
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Chemical Methods of Control
Alcohols and aldehydes Alcohols 70% ethyl alcohol (ethanol) Isopropyl alcohol (isopropanol) Aldehydes Formaldehyde (formalin) Glutaraldehyde
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Chemical Methods of Control
Detergents and phenols Detergents Strong wetting agents Surface tension reducers Dissolve microbial cell membranes Phenols Also known as phenolics Lysol
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Antibiotics Figure 11.14: The sites of activity of various antibiotics on a bacterial cell
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Antibiotics The first antibacterials Paul Ehrlich Gerhard Domagk
Magic bullets Harm bacterial pathogens and not host Arsphenamine Firs syphilis treatment Contains arsenic Gerhard Domagk Prontosil Active ingredient: sulfonalamide
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Antibiotics: Sulfonilamide
Figure 11.10a,b,c: How sulfanilamide works to kill bacteria
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Antibiotics Cephalosporins and aminoglycosides Cephalosporins
Like penicillin Produced by Cephalosporium 6-membered ring, as opposed to penicillins’ 5-membered ring Cephalexin ( trade name Keflex) Cephalothin (Keflin) Cefotaxime (Claforan) Ceftriaxone (Rocephin) Ceftaxidime (Fortaz)
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Antibiotics Cephalosporins and aminoglycosides Aminoglycosides
Useful against Gram-negative bacteria Streptomycin Major early weapon against tuberculosis Now most Mycobacterium tuberculosis is resistant Most produced by Streptomyces Inhibit protein synthesis Gentamicin Neomycin
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Antibiotics Broad-spectrum antibiotics
Inhibit or kill many different microbes First one discovered: chloramphenicol Extremely toxic Still used in dire situations Tetracyclines Minocycline Doxycycline Used especially for Gram-negative infections Few side effects Resistance Fungal superinfection Light sensitivity Deposition in teeth
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Antibiotics Other antibiotics Macrolides Vancomycin Streptogramins
Inhibit protein synthesis Erythromycin Azithromycin (Zithromax) Clarithromycin (Biaxin) Vancomycin Inhibits cell wall synthesis in Gram-positive bacteria Severe side effects Streptogramins Quinupristin plus dalfopristin (Synercid)
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Antibiotics Other antibiotics Rifampin Bacillus-produced antibiotics
Inhibits RNA polymerase Synthetic First used against M. tuberculosis Useful against Neisseria, Haemophilus Bacillus-produced antibiotics Only used topically because of toxicity Bacitracin Inhibits cell wall synthsis Effective against Gram-positive bacteria Polymyxin B Inhibits plasma membranes Effective against Gram-negative bacteria
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Antibiotics Antiviral and antifungal antibiotics Antiviral chemicals
NOT antibiotics Amantadine Acyclovir Antifungal antibiotics Nystatin Useful against Candida albicans Reacts with sterols specifically present in fungal membranes Griseofulvin Ringworm Amphotericin B (Fungizone) Fungal infections of internal organs Imidazoles Clotrimazole (Lotrimin) Miconazole (Monistat)
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Antibiotics Antibiotic resistance
Spreading through bacterial populations Bacterial pneumonia Streptococcal blood disease Gonorrhea Staphylococcal infections Tuberculosis Means of resistance Destruction of antibiotic Prevention of uptake Alteration of metabolic pathway Mutation that prevents antibiotic binding or efficacy
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Antibiotics Antibiotic resistance Overuse of antibiotics
Overdose of antibiotics Abuse in developing countries Use in animal feeds Resistance gene transfers from one bacterium to another Shigella Salmonella Staphylococcus Alternatives to reduce resistance or increase efficacy New antibiotics Limited antibiotic use Phage therapy
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