controlling microbes not too hot to handle 11. looking ahead on completing this chapter, you should...
TRANSCRIPT
Controlling Microbes
Not Too Hot to Handle
11
Looking AheadOn 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 m to 0.5 m 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 ControlDisinfection 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 ControlPhenols 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
AntibioticsThe 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
AntibioticsPenicillins
• 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
AntibioticsCephalosporins and aminoglycosides
• Cephalosporins• Like penicillins, contain beta lactam core• 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®)
AntibioticsCephalosporins 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
AntibioticsBroad-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
AntibioticsOther 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®)
AntibioticsOther 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
AntibioticsAntiviral 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®)
AntibioticsAntibiotic 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
AntibioticsAntibiotic resistance
• Alternatives to reduce resistance or increase efficacy• New antibiotics• Limited antibiotic use• Phage therapy