Ch.6 : Microbial Growth Flashcards
Physical Requirements for Growth
Temperature
pH
Osmotic Pressure
Chemical Requirements for Growth
CARBON NITROGEN PHOSPHOROUS Sulfur Trace Elements Oxygen Organic Growth Factor
Microbes classified into 3 groups based on temperature
Psychrophiles
Mesophiles
Thermophiles
Psychrophile
Cold-loving microbes. 0-20 Degrees Celsius
Mesophile
Moderate-temperature loving microbes 20-45 Degrees Celsius
Most disease-causing bacteria prefer 35-40 Degrees Celsius
Thermophiles
heat-loving microbes. 55-85 Degrees Celsius
*Psychrotrophs
0-35 Degrees Celsius
*Hyperthermophiles
85-113 Degrees Celsius
Minimum Growth Temperature
Lowest temperature at which the species will grow
Optimum Growth Temperature
Temperature which species grow best.
Microbes cannot regulate internal temperature
Maximum Growth Temperature
Highest temperature at which growth is possible.
High temperatures may inhibit enzyme functioning and be lethal.
Acidophiles
growth optimum between pH 0 and pH 5.5
Neutrophiles
growth optimum between pH 5.5 and pH 7
Alkaliphiles (alkalophiles)
growth optimum between pH 8.5 and pH 11.5
Plasmolysis
Shrinkage of cell’s cytoplasm
Microorganisms composition is 80-90% water
Hypotonic
Increase osmotic pressure (cell fills up)
Hypertonic
Decrease osmotic pressure (cell shrivels)
Trace Elements
Iron, Copper, Molybdenum, Zinc
Essential for the functions of certain enzymes, usually as cofactors. Too much is toxic
Halotolerant microbe found on human skin
Staphylococcus aureus
Halo = Salt
Obligate Aerobes
absolute requirement for oxygen
ex. Pseudomonas
Obligate Anaerobes
cannot tolerate any oxygen (toxic)
ex. Clostridium
Facultative Anaerobes
grow better with oxygen, but can grow just fine without it also; facultative means flexible
ex. E. coli
microaerophiles
require small amounts of oxygen (2-10%) but large amounts are toxic
ex. Helicobactern pylori
aerotolerant anaerobes
indifferent to oxygen; can grow in the presence of oxygen, but never use it to produce energy; obligate fermenters
ex. Streptococcus pyogenes (strep throat), lactic acid bacteria
Singlet Oxygen
O2- that has been boosted into a higher energy state and is extremely toxic
Superoxide free radicals
A toxic anion (O2-) with an unpaired electron
Must produce superoxide dismutase (SOD) to neutralize
Peroxide Anion
An oxygen anion consisting of two atoms of oxygen (O2^-2)
Must produce catalase to neutralize it
Hydroxyl Radical
A toxic form of oxygen (OH) formed in cytoplasm by ionizing radiation and aerobic respiration
Fastidious Organisms
organisms that cannot synthesize everything they need and require supplemental growth factors
ex. Neisseria (need all 20 aa, 7 vitamins), Mycoplasma
Non-Fastidious Organisms
versatile, do not require supplemental growth factors
ex. E. coli, P. aeruginosa
Biofilms
A microbial community that usually forms as a slimy layer on a surface
Can be formed on any conditioned surface; Hard to remove
Very complex communities
Quorum sensing
Cell-to-cell chemical communication allows bacteria to coordinate their activity and group together into communities.
Planktonic
Free swimming bacterium
Sessile
Grow attached to surfaces
Extracellular Polymeric substance (EPS)
a glycocalyx that permits bacteria to attach to various surfaces
Binary Fission
Prokaryotic cell reproduction by division into two daughter cells
Lag Phase
The time interval in a bacterial growth curve during which there in no growth
Log phase
The period of bacterial growth or logarithmic increase in cell numbers; also called exponential growth phase
Stationary Phase
The period in a bacterial growth curve when the number of cells dividing equals the number of dying
Death Phase
The period of logarithmic decrease in a bacterial population; also called logarithmic decline phase
Direct Measurement (counting chamber)
counts both live and dead cells
Indirect Measurement (Spectrophotometry)
measures absorption or transmittance of light at 600nm wavelength
both live and dead cells absorb light
Turbidity
the cloudiness of a suspension
Direct Measurement (Viable Cell Count)
*also called Dilution plating
counts only live cells
each viable cell leads to a colony
count colony forming units (cfu)
