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• Sterilization
– The killing or removal of all viable organisms within a growth medium
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• Inhibition
– Effectively limiting microbial growth
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• Decontamination
– The treatment of an object to make it safe to handle
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• Disinfection
– Directly targets the removal of all pathogens, not necessarily all microorganisms
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• Heat sterilization
- is the most widely used method of controlling microbial growth (Figure 26.1)
- – High temperatures denature macromolecules
- – Amount of time required to reduce viability tenfold is called the decimal reduction time (Figure 26.2)
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___-___ ___ can survive heat that would rapidly kill vegetative cells
• Spore-forming bacteria
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The autoclave
- is a sealed device that usessteam under pressure (Figure 26.3)
- – Allows temperature of water to exceed
- – Not the pressure that kills, but the high temperature
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Pasteurization
- is the process of using precisely controlled heat to reduce the microbial load in heat-sensitive liquids
- – Does not kill all organisms, it is not sterilization
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Radiation Sterilization
- • Microwaves, UV, X-rays, gamma rays can reducemicrobial growth
- • UV has sufficient energy to cause modifications and breaks in DNA
- – UV is useful for decontamination of surfaces (Figure 26.4)
- – Cannot penetrate solid, opaque, or light-absorbingsurfaces
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Ionizing radiation
- – Electromagnetic radiation that produce ions andother reactive molecules
- – Generates electrons, hydroxyl radicals, and hydride radicals
- – Some microorganisms are more resistant to radiation than others
- • Amount of energy required to reduce viability tenfold is analogous to D value (Figure 26.5)
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Sources of radiation include ___ and radioactive ___
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Radiation is used for ___ in the medical field and food industry
sterilization
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Radiation is approved by the WHO and is used in the USA for ___ of ___ particularly susceptible to microbial contamination
- decontamination of foods
- • Hamburger, chicken, spices may all be irradiated
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Depth filters
- – HEPA(High-efficiency particulate air) filters
- -filters that filter though out the medium as opposed to just at the surface. Reduces ability to be clogged
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Membrane filters
– Function more like a sieve
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nucleation track (nucleopore) filter
- -thin polycarbonate films that are perforated by a combined treatment with radiation and chemicals.
- -work like sieves, preventing the flow of any particle with a size greater than the pore.
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bacteriostatic
- stops cell growth
- viable cell count=total cell count
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bacteriocidal
- bacteria is killed but not destroyed
- viable cell count is decreased
- total cell count stays constant (bacterial cells linger after death)
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bacteriolytic
- bacterial cells are destroyed
- viable and total cell count drops
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Minimum inhibitory concentration (MIC)
- the smallest amount of an agent needed to inhibit growth of a microorganism
- – Varies with the organism used, inoculum size,temp, pH, etc.
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Disc diffusion assay
– Antimicrobial agent added to filter paper disc– MIC is reached(bacteria is killed and lawn cleared) at some distance away from disc
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Zone of inhibition
– Area of no growth around filter paper disc
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antimicrobial agents can be divided into two categories:
- – Products used to control microorganisms in commercial and industrial applications
- • Examples: chemicals in foods, air-conditioning cooling towers, textile and paper products, fuel tanks
- – Products designed to prevent growth of human pathogens in inanimate environments and on external body surfaces
- • Sterilants, disinfectants, sanitizers, and antiseptics
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Cold sterilization
a process in which sterilization is carry out at low temperature with the help of chemicals, radiations, membranes and all other means excluding high temperature.
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Antibiotics
antimicrobial agents created by organisms naturally
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Antimicrobial drugs are classified on the basis of: (3 classifications)
- – Molecular structure
- – Mechanism of action
- – Spectrum of antimicrobial activity(range of microorganisms effected)
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selective toxicity
- -Selective toxicity is ability to inhibit or kill a pathogen without affecting the host
- -studied by Paul Ehrlich in the early 1900s
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Salvarsan
–one of the first antimicrobial drugs
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Growth factor analogs
- molecules structurally similar to growth factors but do not function in the cell
- – Analogs similar to vitamins, amino acids, andother compounds
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Sulfa drugs:
- – Inhibit growth of bacteria by use of a paraminobenzoic acid analog (sulfanilamide is thesimplest;
- -discovered by Gerhard Domagkin the 1930s
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Isoniazid
- a growth analog effective only against Mycobacterium
- – Interferes with synthesis of mycolic acid (cell wall)
- effective against: Mycobacterium tuberculosis ect...
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Nucleic acid base analogs
formed by the addition of bromine or fluorine to nucleic acid
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Quinolones
- synthesized antibacterial compounds that interfere with DNA gyrase
- e.g., ciprofloxacin
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DNA gyrase
supercoiling of DNA in bacteria
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semisynthetic Antibiotics
- -antibiotics that are modified to enhance efficacy
- – Less than 1% of known antibiotics are clinically useful
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B-Lactam antibiotics
- -one of the most important groups of antibiotics of all time
- -Named for B-lactam ring
- – Include penicillins, cephalosporins, and cephamycins
- – Over half of all antibiotics used worldwide
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Penicillins
(discovered by)
(effective against)
- – Discovered by Alexander Fleming
- – Primarily effective against gram-positive bacteria
- – Some synthetic forms are effective against some gram-negative bacteria
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mechanism of B-lactam antibiotics
inhibitors of cell wall synthesis, specifically transpeptidation (cross-linking of two glycan-linked peptide chains)
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Cephalosporins
- – Produced by fungus Cephalosporium
- – Same mode of action as the penicillins (B-lactam ring) but broader range
- – Commonly used to treat gonorrhea
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Aminoglycosides
- -antibiotics created by Bacteria that contain amino sugars bonded by glycosidic linkage
- -target 30s sub unit of ribosome
- -Examples: kanamycin, neomycin, streptomycin
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• Neurotoxicity and nephrotoxicity
- -Antibiotics created by bacteria not commonly used today
- - Considered reserve antibiotics for when other antibiotics fail
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Macrolides
- -Bacteria synthesized antibiotics that contains lactone rings bonded to sugars
- Example: erythromycin
- – Broad-spectrum antibiotic that targets the 50S subunit of ribosome
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Tetracyclines
- -Bacteria synthesized antibiotics that contain four rings
- – Widespread medical use in humans and animals
- – Broad-spectrum inhibition of protein synthesis
- – Inhibits functioning of 30S ribsomal subunit
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Antimicrobial drug resistance
– The acquired ability of a microorganism to resist the effects of a chemotherapeutic agent to which it is normally sensitive
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six ways that microorganisms can be resistant to an antibiotic
- 1 Organism lacks structure the antibiotic inhibits
- 2 Organism is impermeable to the antibiotic
- 3 Organism can inactivate the antibiotic
- 4 Organism may modify the target of the antibiotic
- 5 Organism may develop a resistant biochemical pathway
- 6 Organism may be able to pump out the antibiotic(efflux)
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Methicillin-resistant S. aureus (MRSA)
one of the few pathogens that have developed resistance to all known antimicrobial agents
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