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Phases of growth can be performed with a bacterial growth curve
- lag phase
- log phase
- stationary pahse
- death phase
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Lag phase
- i. Lag phsase: number of cells changes very little; cells are not dormant; microbial population is undergoing a period of intense metabolic activity involving, in particular, synthesis of enzymes and various molecules
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Log Phase
ii. Log phase: cells begin to divide and grow rapidly; generation time is not constant; time when cells are most active metabolically
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Stationary phase
i. Stationary phase: growth rate slows and number of microbial deaths balances the number of new cells, and the population stabilizes
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Death phase
i. Death phase: number of deaths exceeds number of new cells formed and population enters death phase; phase continues until population is diminished to a tiny fraction of the number of cells in the previous phase or until the population dies out entiremly
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a. Direct Measurement of Microbial Growth
i. Population numbers recorded as __
ii. More commonly done in a series of __
iii. Plate counts: advantageous because it __; disadvantageous in that it __
- number of cells in mL of liquid or gram of solid material
- dilutions
- measures number of viable cells
- takes some time for visible colonies to form
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1. Plate counts assume that each live bacterium can grow __
a. Plate counts are often reported as __
2. When performing this, it is important that only a __
- lined in chains or as clumps
- colony-forming units (CFU)
- limited number of colonies develop in the plate
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i. __: diluting large concentrations of bacteria to make it more feasible to read
ii. Pour Plates and Spread Plates
1. __: 1.0 mL or 0.1 mL of dilutions of bacterial suspension is introduced into a __; the nutrient medium is poured over the sample and then mixed into mediumà solidifiesà incubatedà colonies grow within nutrient agar, as well as on surface
a. Bad because some heat-sensitive microbes may be damaged; it also alters the appearance of some bacteria
- Serial dilutions
- Pour plate method
- Petri Dish
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1. __: 0.1 mL inoculum is added to the surface of a prepoured, solidified agar medium; inoculum is then spread uniformly over the surface of the medium with a specially shaped, sterilized glass, or metal rod
Spread plate method
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i. __: water passed through thin membrane to filter out bacteriaà filter transferred to Petri dish
ii. __: based on the fact that the greater the number of bacteria in a sample, the more dilution is needed to reduce the density to the point at which no bacteria are left to grow in the tubes in a dilution series; most useful when microbes __
- Filtration
- Most Probably Number (MPN) Method
- will not grow on solid media
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i. __: measured volume of a bacterial suspension is placed within a defined area on a microscopic slide; afterwards, a slide is made
1. __
2. Motile bacteria are hard to count by this method; and, dead cells are counted as live onesà both are disadvantageous
- Direct Microscopic Count
- Petroff-Hausser cell center
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a. Estimating Bacterial Numbers by Indirect Methods
i. __: monitors bacterial growth; as bacteria multiply in liuid medium, the medium becomes __
1. A __is used, in which a beam of light is transmitted through a bacterial suspension to a light-sensitive detector
a. As bacterial numbers increase, less light will reach the detector à percentage of transmission
- Turbidity
- turbid, or cloudy with cells
- spectrophotometer
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i. __: assumes that the amount of a certain metabolic product is in direct proportion to the number of bacteria present
ii. __: for filamentous bacteria and molds
1. Method: fungus is removed from the growth medium, filtered to remove extrameous material, and dried in a dessicator; then, it’s weighed
- Metabolic activity
- Dry weight
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a. The History of Chemotherapy
i. __ is credited with it; and __observed that penicillin was an effective antibiotic against bacteria
1. Mechanism of inhibition: __
ii. __: substance produced by microorganisms that in small amounts inhibits another rmicroorganism
iii. More than half of our __are produced by species of __
iv. Most antibiotics today were discovered by methods that required identifying and growing colonies of antibiotic-producing organisms
1. __ rapidly screen very large numbers of microbes in the serarch for new antibiotics
- Pau Ehrlich
- Fleming
- antibiosis
- Antibiotic
- antibiotics
- Streptomyces
- High-throughput methods
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a. Spectrum of Antimicrobial Activity
i. It is easy to find or develop drugs that are effective against prokaryotes and don’t affect eukaryotes; __ has numerous targets
1. So what is the problem?
ii. Some drugs have a narrow __,or range of different microbial types they affect
- selective toxicity
- The problem is more difficult when the pathogen is a eukaryote since they resemble human host cells
- spectrum of microbial activity
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i. Antibiotics that affect a broad range of gram-positive or gram-negative bacteria are called __
ii. A primary factor involved in the __ of antibacterial action lies in the __of gram-negative bacteria and the __ that form water-filled channels across this layer.
1. Drugs that pass through the porin channels must be __. Drugs that are __do not enter gram-negative bacteria readily
- broad-spectrum antibiotics
- selective toxicity
- lipopolysaccharide outer layer
- porins
- small or hydrophilic
- lipophilic
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i. Advantage of broad-spectrum drug: __
ii. Disadvantage of broad-spectrum drug: __
1. Because normal microbes ordinarly compete with and check pathogen growth, an antibiotic that destroys the competitors allows __
a. __may occur, which may lead to a __, a term also applied to growth of a target pathogen that has developed resistance ot the antibiotic
- saving valuable time
- drugs destroy many normal microbes in the host
- survivors to flourish and become opportunistic pathogens
- Overgrowth
- superinfection
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a. The Action of Antimicrobial Drugs
i. They are either __(they kill microbes directly) or __(they prevent microbes from growing)
ii. In bacteriostasis, what happens?
- bactericidal
- bacteriostatic
- the host’s own defenses usually destroy the microorganism
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i. Inhibiting cell wall synthesis
- 1. Penicillin and certain other antibiotcs prevent the synthesis of intact peptidoglycan; the cell wall, as a result, is greatly weakened, and the cell lyses
- a. Only actively growing cells are affected
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i. Inhibiting protein synthesis
1. Due to structural differences in euk and pro ribosomes, eukaryotes have __ and prokaryotes have __ ribosomes
a. This difference accounts for __
i. Since mitochondria of eukaryotes also has __, they can sometimes be affected
- 80S
- 70S
- selective toxicity of antibiotics that affect protein synthesis
- 70S
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i. Injuring the plasma membrane
1. Changes in __ take place, resulting in __
ii. Inhibiting nucleic acid synthesis
1. __
- the permeability
- loss of important metabolites form microbial cell
- DNA replication and transcription is affected
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i. Inhibiting Synthesis of essential metabolites
1. Sometimes, __ can affect synthesis in that it does what?
a. Ex: PABA is a substrate for an enzymatic reaction leading to the synthesis of __, a vitamin that functions as a coenzyme for the synthesis of the purine and pyrimidine bases of nucleic acids and many amino acids
- competitive inhibition
- competes with the substrate for the active site, reducing the amount of product that is formed
- folic acid
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