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11 Controlling Microbes Not Too Hot to Handle Looking Ahead On completing this chapter, you should be able to: • Summarize factors that influence the effectiveness of agents used for microbial control • Explain some of the physical methods of control used to achieve sterilization and destroy all forms of microbes • Compare the chemical methods of microbial control to the physical methods with respect to the anticipated objectives • Identify some of the important chemical agents used to slow the growth of microbes on skin and on objects Looking Ahead On completing this chapter, you should be able to: • Explore the advantages and disadvantages of using antibiotics to control microbes in the body • Identify some of the important antibiotics used to treat disease and indicate how these drugs achieve their antimicrobial activity • Discuss the problem of antibiotic resistance with reference to its cause and implications Physical Methods of Control Heat is a great sterilizing agent Boiling cannot inactivate spores Radiation is a great sterilizing agent Deinococcus radiodurans resists high levels of radiation, too, though! 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 Physical Methods of Control 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 Physical Methods of Control Heat methods • Dry heat • 160 to 170 °C for at least 2 hours • Oxidation of proteins • Necessary for materials that cannot be autoclaved or pasteurized Physical Methods of Control: Heat Physical Methods of Control Radiation • Ionizing radiation • X rays • Gamma rays • About 10,000 times more energetic than UV light • Sterilizing • Creation of oxygen and hydroxyl free radicals that inactivate proteins and DNA Physical Methods of Control Radiation • Electron Beams • Room Temperature Treatment • Can pass through packaging to sterilize contents • Ultraviolet radiation • Results in mutations • Effective against spores, since no repair mechanism 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 Physical Methods of Control Drying • Lyophilization • Osmotic drying • Salt • Sugar • Spices 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 Physical Methods of Control Filtration and refrigeration • Refrigeration • Slows down enzymatic reactions • Only slows microbial growth • Refrigerated foods are not sterile 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 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 and inactivate infectious agents • Stable over time • Nontoxic to humans and animals Chemical Methods of Control General principles • Ideal agent (cont’d) • 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 • Cost effective Chemical Methods of Control Alcohols and aldehydes • Alcohols • 70% ethyl alcohol (ethanol) • Isopropyl alcohol (isopropanol) • Aldehydes • Formaldehyde (formalin) • Glutaraldehyde Chemical Methods of Control Halogens and heavy metals • Halogens • Iodine • Tincture (2% iodine in ethanol) • Iodophor (iodine plus detergent) • Betadine® • Wescodyne® • Chlorine • 5% sodium hypocholorite (bleach) Chemical Methods of Control Halogens and heavy metals • Heavy metals • Silver (as silver nitrate) • Mercury (as Merchurochrome®, Merthiolate®, or thimerosal) • Copper • Copper sulfate • Bordeaux mixture (copper sulfate with lime) Chemical Methods of Control Phenols and detergents • Phenols • Also known as phenolics • Ortho-phenylphelnol • Hexylresorcinol • Hexachlorophene • Chlorhexidine • Trichlosan • Detergents • Strong wetting agents • Surface tension reducers • Dissolves microbial cell membranes Chemical Methods of Control: Phenolics Chemical Methods of Control Ethylene oxide • Small molecule • Great penetration capacity (gas) • Sporicidal • Highly toxic • Explosive • Chemical counterpart of autoclave Antibiotics Antibiotics The first antibacterials • Paul Ehrlich • Magic bullets • Harm bacterial pathogens and not host • Arsphenamine • Firs syphilis treatment • Contains arsenic • Gerhard Domagk • Prontosil • Active ingredient: sulfonilamide Antibiotics: Sulfonilamide Antibiotics The development of penicillin • Alexander Fleming • Penicillium mold on Staphylococcus plates • Clearings where mold was growing • Howard Florey and Ernst Chain • Industrial production of penicillin • Helped fight infections during World War II © Science Source, photo by Dean Pausett/Photo Researchers, Inc. © National Library of Medicine Antibiotics Penicillins • Beta lactam core • Primarily active against Gram-positive bacteria • Block formation of peptidoglycan in cell wall • Penicillinase • Improved penicillins • Penicillin G • Amoxicillin • Ampicillin • Methicillin • Carbenicillin • Ticarcillin Antibiotics: Penicillins Antibiotics Cephalosporins and aminoglycosides • Cephalosporins • Like penicillins, contain beta lactam core • Produced by Cephalosporium • 6-membered ring, as opposed to penicillins’ 5membered ring • Cephalexin ( trade name Keflex) • Cephalothin (Keflin) • Cefotaxime (Claforan®) • Ceftriaxone (Rocephin®) • Ceftaxidime (Fortaz®) 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 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 Antibiotics Broad-spectrum antibiotics • Tetracyclines (cont’d) • Few side effects • Resistance • Fungal superinfection • Light sensitivity • Deposition in teeth Antibiotics Other antibiotics • Macrolides • Inhibit protein synthesis • Erythromycin • Azithromycin (Zithromax ®) • Clarithromycin (Biaxin®) • Vancomycin • Inhibits cell wall synthesis in Gram-positive bacteria • Severe side effects • Streptogramins • Quinupristin + dalfopristin (Synercid®) Antibiotics Other antibiotics • Rifampin • 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 synthesis • Effective against Gram-positive bacteria Antibiotics Other antibiotics • Bacillus-produced antibiotics (cont’d) • Polymyxin B • Inhibits outer membranes • Effective against Gram-negative bacteria 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 Antibiotics Antiviral and antifungal antibiotics • Antifungal antibiotics (cont’d) • Amphotericin B (Fungizone®) • Fungal infections of internal organs • Imidazoles • Clotrimazole (Lotrimin®) • Miconazole (Monistat®) 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 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 Antibiotics Antibiotic resistance • Alternatives to reduce resistance or increase efficacy • New antibiotics • Limited antibiotic use • Phage therapy