Ch 6 – Microbiology Test Questions – Flashcards
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| steps of binary fission |
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| -cell elongates and DNA is replicated -cell wall and plasma membrane begin to constrict -cross wall forms completely separating DNA -cell separates |
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| other ways bacteria can reproduce |
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| -budding -fragmenting or conidiospores |
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| bacterium that reproduces by budding |
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| caulobacter |
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| bacterium that fragments or forms conidiospores |
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| filamentous bacteria |
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| lag phase |
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| -very little change in cell number -synthesis of enzymes and various molecules (cell adapt) |
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| log (exponential growth) phase |
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| -cell reproduction is most active -general time is constant -exponential increase in population |
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| stationary phase |
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| -growth rate slows -cells dying = new cells -due to exhaustion of nutrients, build up of waste, change in pH |
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| death phase |
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| -number of cells dying is greater than number of new cells -population decreases exponentially |
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| continuous flow culture allows... |
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| maintenance of a culture in a log phase |
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| generation time |
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| time it takes for a population of bacteria to double in number |
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| diauxic growth |
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| -diphasic growth that occurs when cells are growing on a mixture of 2 sugars -cells grow using the fastest metabolizable sugar first (usually glucose) -once it is exhausted there is a brief delay while enzymes needed to metabolize second sugar are synthesized |
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| culture media |
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| -a nutrient material prepared for growth of microorganisms -can be liquid (broth) or solid 9tubes/petri dish) |
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| inoculum |
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| microorganisms initiated into a culture medium to initiate growth |
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| culture |
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| microorganisms that grow and multiply in or on a culture medium |
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| a culture medium must... |
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| -contain appropriate nutrients (source of E,C,N,S,P growth factors) -have sufficient moisture -pH appropriate -suitable oxygen level -be sterile -be incubated at correct temp. |
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| a culture medium must... |
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| -contain appropriate nutrients (source of E,C,N,S,P growth factors) -have sufficient moisture -pH appropriate -suitable oxygen level -be sterile -be incubated at correct temp. |
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| agar |
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| complex polysaccharide derived from algae |
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| what makes agar good for microbio? |
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| -not degraded(only a few microbes can) -liquefies at 100 degrees celsius and remains liquid at temp above 40 celsius -once solidified it remains solid up to temp of 100 degrees celsius |
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| 4 types of culture media |
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| -chemically defined media -complex media -selective media -differential media |
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| chemically defined medium |
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| -exact chemical composition is known -glucose is often used as source of carbon and/or energy |
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| complex medium |
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| -exact composition varies from batch to batch -usually contains yeast, meat, plant, protein (peptones digests -ECNS are provided by proteins -yeast or meat extracts provide vitamins and other organic growth factors |
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| selective medium |
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| -designed to suppress growth of certain microorganisms and promote growth of desired -useful for isolation of specific organism in a mixed culture -Sabouraud's dextrose agar -EMB -Bismuth sulfite agar |
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| Sabouraud's dextrose agar |
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| -used to identify fungi -its pH of 5.6 prevents growth of most bacteria while allowing growth on fungi |
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| EMB |
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| -Eosin methylene blue -selects for Gram negative -E and M inhibit growth of Gram positive -also differential -turns green with lactic acid |
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| Bismuth sulfite agar |
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| -used to isolate Salmonella typhi -bismuth sulfite inhibit Gram+and- |
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| differential medium |
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| -allows to distinguish colonies of desired organisms from others growing on same plate -uses biochemical characteristics or indicators -Blood agar -MacConkey agar |
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| blood agar |
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| -contains RBCs -used to identify bacterial species that destroy RBCs |
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| MacConkey agar |
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| -used to identify bacteria that ferment lactose -contains lactose and dye neutral red to stain bacteria forming lactose -also selective -bile salts and crystal violet inhibit Gram positive organisms |
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| Mannitol salt agar |
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| -contains 7.5% NaCl which inhibits most microorganisms except Staphylococcus -also contains mannitol and pH indictator if mannitol is fermented |
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| enrichment medium |
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| -usually liquid -used to grow bacteria present in small numbers in a sample containing other microorganisms that may be present in large numbers -selective for bacteria that need to be enriched -MS medium |
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| MS medium |
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| -magnesium chloride selenite -used to enrich and isolate Salmonella from feces or other samples -a small inoculum is used to inoculate MS broth -after 48 hours, a small amount is transferred to a new tube of MS broth -after 3-4 transfers, a small inoculum is plated onto a solid MS medium |
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| reducing medium |
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| -used to grow bacteria that cannot tolerate oxygen -contains sodium thioglycolate (inactivates dissolved oxygen) -heated just before to get rid of absorbed oxygen |
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| types of direct measurement |
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| -plate count (CFU) -filtration -most probable number method -direct microscopic count |
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| indirect measurement types |
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| -turbidity -metabolic activity -dry weight |
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| plate counts |
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| -measures number of viable cells -takes some time for colonies to become visible -assume that each cell divides to form a single colony (CFU) -to be accurate plates need to contain 30-300 colonies -serial dilutions must be performed |
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| number of bacteria /ml |
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| number of colonies on plate x reciprocal of dilution |
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| pour plate method |
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| -inoculate empty plate -add melted nutrient agar -swirl -colonies on and in solidified medium |
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| spread plate method |
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| -inoculate plate containing solid medium -spread inoculum over surface evenly -colonies grow on surface medium |
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| pour plate vs spread plate |
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| -pour plate is more accurate -gives lower counts -hot agar may kill some bacteria -reduced growth rates of obligate anaerobes in depth of agar |
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| filtration |
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| -suitable for samples which there is a small amount of bacteria -lakes, streams, -at least 100ml of water passed through a filter with pores -routinely used to detect coliform (fecal contamination) in water and food |
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| most probable method |
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| -useful when organisms grown on solid medium -statistical estimate-the greater the number of present bacteria in a sample, the more dilution is required to reduce the density to a point at which no bacteria are left to grow in the tubes containing the liquid medium |
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| direct microscopic count |
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| -a measure volume of a bacterial suspension is place on a microscope slide within a square centimeter area -several fields are counted -avg/volume = # bacteria/mL -Petroff Hausser cell counter is specially designed for direct cell counting -Coulter counters too |
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| direct microscopic count problems |
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| -motile bacteria hard to count -some dead may be counted as living -high cell concentration is needed -but very rapid, no need for incubation |
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| turbidity |
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| -based on the fact that bacteria multiply in a liquid medium and make it cloudy (turbid) -spec is used -beam of light transmitted through a bacterial suspension -the more bacteria, the less the transmittance -log scales indicates Abs -abs can be matched with plate counts |
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| metabolic activity |
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| -based on the assumption that the amount of metabolic product is proportional to the number of bacteria present -Co2, acids... |
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| dry weight |
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| -useful for filamentous bacteria and molds -fungus or bacteria cultures filtered, dessicated (dried), weighted |
