Controlling Microbial ( micro para Flashcards
FACTORS THAT AFFECT
MICROBIAL GROWTH
Availability of Nutrients
Moisture
Temperature
Microorganisms that grow best at high temperatures are
called
thermophiles
Organisms that favor
temperatures above 100°C are referred to as
hyperthermophiles
Most microorganisms prefer a what ph
neutral or slightly
alkaline growth medium (pH 7.0–7.4)
The highest
temperature at which a bacterium has been found living is
around 113°C; it was an archaeon named
Pyrolobus
fumarii.
Microbes that grow best at moderate temperatures are
called
mesophiles
prefer cold temperatures.
Psychrophiles
prefer warm temperatures
but can endure very cold or even freezing
temperatures.
Psychroduric organisms
prefer a pH of >8.5
– Alkaliphiles
prefer a pH of 2 to 5
– Acidophiles
is the movement of a solvent, through a
permeable membrane, from a lower concentration of
solutes (dissolved substances) to a higher
concentration of solutes.
Osmosis
is the pressure that is exerted on a
cell membrane by solutions both inside and outside
the cell
Osmotic pressure
When the concentration of solutes in the external
environment of a cell is greater than that of solutes
inside the cell, the solution in which the cell is
suspended is said to be
hypertonic.
is a condition in which the cell membrane
and cytoplasm of a cell shrink away from the cell
wall; it occurs when bacteria with rigid cell walls are
placed in a hypertonic solution.
Plasmolysis
When the concentration of solutes outside a cell is
less than that of solutes inside a cell, the solution in
which the cell is suspended is said to be
hypotonic.
If a bacterial cell is placed into a hypotonic solution,
it may not burst (because of the rigid cell wall). If it
does burst, the cytoplasm escapes; this process is
known as
plasmoptysis.
A solution is said to be ___ when the
concentration of solutes outside a cell equals the
concentration of solutes inside the cell.
isotonic
Organisms that prefer to live in salty environments
are called
halophilic organisms.
Those that do not
prefer to live in salty environments but are capable
of surviving there (e.g., Staphylococcus aureus) are
called .
haloduric organisms
Microbes that can survive in high atmospheric
pressure (>14.7 psi) are known as
piezophiles.
prefer the same atmosphere that
humans do (~20%–21% O2 and 78%–79% N2, and
<1% other gases)
Obligate aerobes
require reduced concentrations of
oxygen (~5% O2).
Microaerophiles
require increased concentrations of CO2
(5%–10% CO2).
Capnophiles
are killed by the presence of
oxygen
Obligate anaerobes
