Transcript Ch11_Outline

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