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41 terms

Microbiology Test 2 CH 6

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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