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Micro Exam Ch6
Microbial Growth
| Question | Answer |
|---|---|
| What are the physical requirements for microbial growth? | Temperature, pH, and osmotic pressure |
| What are the chemical requirements for microbial growth? | Sources of carbon, nitrogen, sulfur, phosphorus, oxygen, trace elements and organic growth factors |
| Cold-loving microbes | Psychrophiles |
| Moderate-temperature-loving microbes | Mesophiles |
| Heat-loving microbes | Thermophiles |
| This is the lowest temperature at which a microbial species will grow best | Minimum growth temperature |
| This is the temperature at which a species grows best | Optimum growth temperature |
| This is the highest temperature at which growth is possible | Maximum growth temperature |
| Organisms that are much more common than psychrophiles and are the most likely to be encountered in low-temperature food spoilage because they grow fairly well at refrigerator temperatures | Psychotrophs |
| What biosafety level is this? ·Highly infectious airborne pathogens and agents causing serious or potentially lethal disease ·Biosafety cabinets to prevent airborne transmission ·Example: Mycobacterium tuberculosis | BSL-3 |
| Mesophiles, with an optimum growth temperature of ________, are the most common type of microbe | 25 - 40°C |
| The optimum temperature for many pathogenic bacteria is about ____, and incubators are usually set around this temperature | 37°C |
| How much of the dry weight of a typical bacterial cell is carbon? | 50% |
| What two elements does protein synthesis require? | Nitrogen and sulfur |
| Potassium, magnesium, and calcium are also elements that microorganisms require, often as _____ for enzymes | Cofactors |
| What is the enzyme that breaks down hydrogen peroxide but differs from catalase in that its reaction does not produce oxygen? | Peroxidase |
| What are some examples of organic growth factors? | Vitamins, amino acids, purines, and pyrimidines |
| What is the partial of breakdown of red blood cells in a RBC agar? | Alpha hemolysis |
| What is the first phase of bacterial growth with intense activity preparing for population growth, but no increase in population and can last for 1 hour or several days? | Lag phase |
| Exponential growth stops because the bacteria approach the _____ ______, the number of organisms that an environment can support | Carrying capacity |
| What instrument is used to measure turbidity? A beam of light is transmitted through a bacterial suspension to a light-sensitive detector. As bacterial numbers increase, less light will reach the detector | Spectrophotometer |
| In what plate count method does one inoculate the empty plate, add melted nutrient agar, swirl to mix, and do colonies grow on and in solidified medium? | Pour plate method |
| What is a measure of the acidity or alkalinity of a solution? | pH |
| Most bacteria grow best in a narrow pH range near neutrality, between pH ____ and ____ | 6.5 and 7.5 |
| Molds and yeasts grow between pH _ and _ | 5 and 6 |
| These bacteria grow in acidic environments | Buffer |
| Growth media in the lab contains a _____, such as phosphate salts | Buffer |
| How much water are microorganisms composed of? | 80 - 90% water |
| Hypertonic environments, or an increase in salt or sugar, cause _____ | Plasmolysis |
| These organisms have adapted so well to high salt concentrations that they actually require them for growth | Extreme or obligate halophiles |
| Organisms from the Dead Sea require how much salt? | 30% salt |
| These organisms do not require high salt concentrations but are able to grow at salt concentrations up to 2%, a concentration that inhibits the growth of many other organisms | Facultative halophiles |
| Chemoheterotrophs get most of their carbon from the source of their energy -- organic materials such as ______, _____, and ______ | Proteins, carbohydrates, and lipids |
| Chemoautotrophs and photoautotrophs derive their carbon from ______ _____ | Carbon dioxide |
| The synthesis of DNA and RNA also require which two elements, as does the synthesis of ATP? | Nitrogen and phosphorus |
| What element do organisms primarily use to form the amino group of the amino acids of proteins? | Nitrogen |
| Some important bacteria, including many of the photosynthesizing cyanobacteria, use gaseous nitrogen (N2) directly from the atmosphere in the process called ______ ______ | Nitrogen fixation |
| What element is used to synthesize sulfur-containing amino acids and vitamins such as thiamine and biotin? | Sulfur |
| Important natural sources of ______ include the sulfate ion (SO₄²-), hydrogen sulfide (H₂S), and the sulfur-containing amino acids | Sulfur |
| What element is essential for the synthesis of nucleic acids and phospholipids of cell membranes? | Phosphorus |
| PO43- (phosphate ion) is a source of what element? | Phosphorus |
| Microbes require very small amounts of other mineral elements; these are referred to as ____ _____ | trace elements |
| What are four examples of trace elements? | Iron, copper, molybdenum, zinc |
| Most trace elements are enzyme _______ | Cofactors |
| This element is required for some microbes while deadly for others | Oxygen |
| Organisms that require oxygen to live are called ______ _____ | Obligate aerobes |
| Organisms that can use oxygen when it is present but are able to continue growth by using fermentation or anaerobic respiration when oxygen is not available are called _______ ______ | Facultative anaerobes |
| Organisms that cannot grow in the presence of oxygen are called _____ ______ | Obligate anaerobes |
| These organisms only grow anaerobically, but growth continues in the presence of oxygen | Aerotolerant anaerobes |
| These organisms grow in only aerobic conditions, but oxygen is required in low concentration | Microaerophiles |
| What is one of the toxic oxygens that is normal molecular oxygen (O2) that has been boosted into a higher-energy state and is extremely reactive | Singlet oxygen (1O2-) |
| What is one of the toxic oxygens that have an unpaired electron, so are very reactive and will try to steal an electron from another chemical? The chemical that is stolen from will then try to steal from another chemical, and it will continue as a domino | Superoxide radicals (O2-) |
| What enzyme neutralizes the toxic oxygen superoxide radicals? | Superoxide dismutase (SOD) |
| What is one of the toxic oxygens that is the active principle in the antimicrobial agents hydrogen peroxide and benzoyl peroxide? | Peroxide anion |
| What is the enzyme that converts hydrogen peroxide into water and oxygen to detoxify it? | Catalase |
| What is one of the toxic oxygens that is probably the most reactive and is formed in the cellular cytoplasm by ionizing radiation? | Hydroxyl radical |
| What are essential organic compounds an organism is unable to synthesize that must be directly obtained from the environment? | Organic growth factors |
| In nature, microorganisms typically live in communities called ______, which are a thin, slimy layer encasing bacteria that adheres to a surface | Biofilms |
| What is cell to cell communication that allows bacteria in a biofilm to coordinate their activities with one another? | Quorum sensing |
| What is NOT a characteristic of biofilms? A. Can be a single species or many B. Grow in a uniformly thick monolayer C. Provides shelter from harmful factors or the host's immune system D. Can share nutrients | B. Grow in a uniformly thick monolayer |
| An estimated __% of human bacterial infections involve biofilms | 70% |
| What are some indwelling medical devices that biofilms form on? | Mechanical heart valves, catheters, etc. |
| What is a nutrient material prepared for the growth of microorganisms in a laboratory called? | Culture medium |
| What are microbes that are introduced into a culture medium to initiate growth called? | Inoculum |
| What are the microbes that grow and multiply in or on a culture medium referred to as? | Culture |
| What method is used to isolate pure cultures? | Streak plate method |
| What is a population of cells arising from a single cell or spore (or from a group of attached cells)? | Colony |
| A medium with initially no living microorganisms in it is ______ | Sterile |
| What two containers are used to grow bacteria? | Test tubes and petri dishes |
| What medium is in liquid form? | Nutrient broth |
| What medium is used as solidifying agent for culture media in Petri plates, slants, and deeps? | Agar |
| What medium is a complex polysaccharide derived from a marine alga? | Agar |
| What contain agar that has solidified while the test tube was held at an angle? | Slants |
| What contain agar that has solidified while the test tube was upright? | Verticals |
| What temperature does agar liquefy at? | 100°C |
| What temperature does agar solidify at? | 40°C |
| What is a medium whose exact chemical composition is known? | Chemically defined medium |
| What is a medium that extracts and digests of yeasts, meat, or plants? | Complex media |
| Media vs medium | Media = plural, medium = singular |
| When agar is added to a nutrient broth, it is called _____ _____ | Nutrient agar |
| What is the complete breakdown of red blood cells in a RBC agar? | Beta hemolysis |
| What is it called when red blood cells are not broken down in a RBC agar? | Gamma Hemolysis |
| Because anaerobes might be killed by exposure to oxygen, special media called ______ ____ must be used. These media contain ingredients, such as sodium thioglycolate, that chemically combine with dissolved oxygen and deplete the oxygen in the culture medi | Reducing media |
| What are microbes that grow better at high CO2 concentrations called? | Capanophiles |
| What media are designed to suppress the growth of unwanted bacteria and encourage the growth of the desired microbes? | Selective media |
| What media make it easier to distinguish colonies of the desired organism from other colonies growing on the same plate? | Differential media |
| T or F: Sometimes selective and differential characteristics are combined in a single medium | True |
| Because bacteria present in small numbers can be missed, even if other bacteria are present in much larger numbers, it is often sometimes necessary to use an _______ ______. The medium is liquid and provides nutrients and environmentconditions that favor | Enrichment culture |
| What biosafety level is this? ·Microorganisms that are considered nonpathogenic ·Use standard microbiological practices ·Example: Lactobacillus casei | BSL-1 |
| What biosafety level is this? ·Moderate risk of infection ·Lab coat, gloves, eye protection, biohazardous waste ·Example: Salmonella enterica | BSL-2 |
| What biosafety level is this? ·Dangerous and infectious pathogens with a high risk of aerosol-transmitted infections that are life threatening, treatment or vaccines unavailable ·Exhaust air is filtered twice; full-body, positive pressure personnel suit | BSL-4 |
| What are two common methods of preserving microbial cultures for long periods? | Deep-freezing and lyophilization |
| What is a process in which a pure culture of microbes is placed in a suspending liquid and quick-frozen at temperatures ranging from - 50°C to -95°C? (The culture can usually be thawed and cultured even several years later) | Deep-freezing |
| What is the process in which a suspension of microbes is quickly frozen at temperatures ranging from -54°C to -72°C and the water is removed by a high vacuum (sublimation)? | Lyophilization (freeze-drying) |
| By what process do bacteria normally reproduce? | Binary fission |
| What form of bacterial reproduction do some bacteria do where they form a small initial outgrowth (a bud) that enlarges until its size approaches that of the parent cell, and then it separates? | Budding |
| Bacteria reproducing in _____ ______ do not require a mitotic spindle or a nucleus membrane | Binary fission |
| What is the time required for a cell to divide (and its population to double) called? | Generation time |
| What is the typical generation time for a bacterial cell? | 1 to 3 hours |
| What are some of the physical and chemical conditions that bacteria are highly dependent on to reproduce for the shortest generation time? | Temperature, nutrient availability, etc. |
| What bacteria can double every 20 minutes under favorable conditions? | E. coli |
| What is a diagram that shows the growth of cells over time? | Bacterial growth curve |
| What are the four phases of growth? | 1. Lag phase 2. Log phase 3. Stationary phase 4. Death phase |
| What is the second phase of bacterial growth where the cells begin to divide and enter a period of growth or logarithmic increase? | Log phase, or exponential growth phase |
| What is the third phase of bacterial growth where the growth rate slows, and the cells enter a period of equilibrium, and the number of microbial deaths balances the number of new cells, and the population stabilizes? | Stationary phase |
| What is the fourth phase of bacterial growth where the population is decreasing at a logarithmic rate? | Death phase |
| What are the three direct methods of measuring microbial growth? | Plate counts, microscopic count, filtration |
| What is an indirect method for measuring microbial growth? | Turbidity |
| What is the most frequently used method of measuring bacterial populations which measures the number of viable cells in the culture? | Plate count |
| What do plate counts measure? | Colony-forming units (CFU) |
| What are the disadvantages to plate counts? | Incubation period required, counts may be inaccurate for microbes that grow in clusters |
| To ensure that plate colony counts will be within the range of 30 to 300 colonies, the original inoculum is diluted several times in a process called _____ ______ | Serial dilution |
| In what plate count method does one inoculate the plate containing the solid medium, spread inoculum evenly over the surface, and do colonies grow only on the surface medium? | Spread plate method |
| What direct method of measuring microbial growth requires at least 100 ml of water to be passed through a thin membrane filter whose pores are too small to allow bacteria to pass? | Filtration |
| In what method of measuring microbial growth is a statistical estimate technique used to determine the number of bacteria? | Most probable number (MPN) method |
| In what direct method of measuring microbial growth is a measured volume of a bacterial suspension placed within a defined area on a microscope slide? | Direct microscopic count |
| As bacteria multiply in a liquid medium, the medium becomes _____, or cloudy with cells | Turbid |
Created by:
malele-sedlacek
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