Microbiology Test 2 CH 6
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41 terms
Terms | Definitions |
|---|---|
 psychrophiles | 15 C; polar regions; extremely cold |
| psychrotrophs | 20-30C; spoilage of refrigerated foods |
| mesophiles | about 37C; most pathogens and spoilage organisms; most common microbes |
| thermophiles | compost piles, spoilage of canned goods, optimum is 80 C or higher |
| hyperthermophiles | hydrothermal vents, hot springs; extremely hot, optimum is 80C or higher |
| molds and yeasts can grow | 5-6 pH |
| most bacteria can grow | 6.5-7.5 pH |
| osmotic pressure | a physical growth requirement; can have the effect of removing water from a cell |
| plasmolysis | shrinkage of the cell's cytoplasm |
| carbon | necessary for structural organic molecules, energy source |
| nitrogen | necessary in amino acids, proteins, and nucleic acids; most bacteria decompose proteins (NH4+ or NH3-), N2 in nitrogen fixation |
| sulfur | necessary in amino acids (cys, met), thiamine and biotin (vitamins); use SO4(2-) or H2S to decompose proteins |
| phosphorus | necessary in DNA, RNA, ATP, and membranes (phospholipids); PO4(3-) |
| trace elements | necessary inorganic elements required in small amounts usually as enzyme cofactors EX- zinc, iron, magnesium |
| obligate aerobes | require O2 to grow, grow at top of tube |
| facultative anaerobes | grow better with O2, but can grow without it; don't have SOD (superoxide dismutase) so can't make catalase or peroxides |
| aerotolerant anaerobes | fermenters, don't care about O2-irrelevant; grow dispersed |
| micro-aerophiles | need some O2; grow in the middle of tube |
| superoxide dismutase (SOD) | enzyme that can neutralize the superoxide free radicals (O2-) which are very toxic to the cell, without this, you can not get rid of O2- |
| catalase | converts hydrogen peroxide to water and oxygen (why hydrogen peroxide bubbles on a wound), human tissues contain this |
| peroxidase | enzyme that breaks down hydrogen peroxide but differs from catalase in that its reaction does not produce oxygen |
| chemically defined media | EXACT chemical composition is known |
| complex media | extracts and digests of yeasts, meat, or plants (nutrient broth, nutrient agar) |
| reducing media | used in the cultivation of anaerobic bacteria because otherwise, anaerobes might be killed by exposure; contain chemicals (thioglycollate or oxyrase) that chemically combine with dissolved oxygen and deplete the oxygen in the culture medium |
| selective media | suppresses unwanted microbes and encourages growth of desired microbes |
| differential media | makes it easy to distinguish colonies of different microbes from each other EX- blood agar |
| agar | complex polysaccharides used as solidifying agent for culture media EX- Petri plates, slants, and deeps |
| colony | a population of cells arising from a single cell or spore (or from a group of attached cells); often called a colony-forming unit (CFU) |
| binary fission | the normal reproductive method of bacteria, in which a single cell divides into two identical cells |
| generation time | the time it takes a cell to divide (or population to double) |
| lag phase | intense metabolic activity preparing for population growth, but no increase in population; "set-up" |
| log phase | logarithmic, or exponential, increase in population; cellular reproduction (division) most active, cells are most active metabolically |
| stationary phase | period of equilibrium; microbial death is balanced with the production of new cells; nutrients deplete |
| death phase | population is decreasing at a logarithmic rate; cell death exceeds number of new cells formed |
| plate count | colony counting method: perform dilutions of a sample, inoculate Petri plates from serial dilutions, and after incubation, count colonies on plates that have 25-250 colonies (CFUs) |
| filtration | colony counting method: bacteria are retained on the surface of a membrane filter and then transferred to a culture medium to grow and subsequently be counted |
| direct microscopic count | colony counting method: the microbes in a measured volume of a bacterial suspension are counted with the use of a specially designed slide |
| turbidity | as bacteria multiply in a liquid medium, the medium becomes turbid or cloudy with cells |
| spectrophotometer | used to measure the turbidity by measuring the amount of light that passes through a suspension of cells; less light transmitted = the more bacterial suspension, counts both the live and dead cells |
| plate count formula | cells/ml= N/ D X V N= number of colonies D= dilution V=volume |
| acidophiles | grow in acidic environments, below a 5 pH generally |
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