BME 245L – Final Exam Study Guide (Biomedical Engineering Laboratory Review,
Practice Questions & Answers)
Steam sterilization (autoclave) - ANS ✔✔Usually 30 minutes at 121 degrees C; Most widely used
and most dependable; Heat compatible:
OK - polypropylene, silicone, metals
Not OK - polystyrene, polyethylene’s
polypropylene - ANS ✔✔conical tubes, microcentrifuge tubes, micropipette tips
polystyrene - ANS ✔✔all of our tissue culture flasks, well plates, serological pipettes; cell
culture: treat w/plasma = less hydrophobic, fibronectin adsorb/cells attach
Ethylene oxide (gas phase sterilization) - ANS ✔✔sterilizing items sensitive to heat;
Residue harmful, aeration to remove residue.
Ionizing radiation (gamma radiation) - ANS ✔✔Provides good penetration, but sometimes
damage surfaces of materials; High cost/not used in health care facilities; Large scale production
(all the conical tubes and flasks, including T75 for tissue culture)
Peracetic acid
Liquid - ANS ✔✔Sterilize equipment with narrow long lumens; endoscopes
Dry heat (oven) - ANS ✔✔autoclave no steam;
Much higher temperatures, longer time; powders if they are not susceptible to heat
Filter sterilization - ANS ✔✔Physically remove particles. ex:
,0.22 um pore filter
Useful for heat sensitive liquids
Ultraviolet light - ANS ✔✔Directional:cannot sterilize surfaces that aren't illuminated.
Poor penetration - UV light does not go through much
Not FDA approved
Lab disinfectants - ANS ✔✔70% Ethanol (more effective than 100%), 10% Sodium hypochloride
(bleach) for mammalian cells; eventually goes bad from light and heat. bad ~ week
Other disinfectants - ANS ✔✔Hydrogen peroxide (3%), Iodine, Phenol, Lysol (quarternary
ammonium compounds)
Disinfection vs. Sterilization - ANS ✔✔•* Disinfection *= Destroying PATHOGENIC microbes
except for spores (ie chemical disinfection, pasteurization)
•* Sterilization *= Killing ALL microbes (good & bad) (ie autoclave, flash sterilization, low temp
sterilization)
in lab words: disinfection is less effective sterilization. Keep the outside of things clean
We sterilize our hands with 70% ethanol before touching anything inside the biological safety
cabinet. - ANS ✔✔False! Disinfect!
Mycoplasma - ANS ✔✔Preventing mycoplasma contamination is difficult. For one, mycoplasma
cells are small (0.3-0.8 µM in diameter) and pleomorphic (8), allowing them to pass through
standard filtration membranes. Secondly, mycoplasmas lack cell walls. This makes them
impervious to cell culture antibiotics that inhibit cell wall synthesis, such as penicillin. Effective
antibiotics do exist, however, their continuous use in cell culture is not recommended due to
, possible cytotoxicity. Third, mycoplasmas are able to reach high concentrations in the media of
infected cells without noticeable turbidity (9). This makes detection via visual inspection
difficult. Lastly, while the primary source of mycoplasma contamination is likely other cell
cultures, mycoplasmas from lab personnel are a potential source as well (7). Hence, the only
reliable ways to minimize contamination are to test routinely (and frequently), practice safe cell
culture techniques and to obtain cells from reputable sources such as the American Type
Culture Collection (ATCC).
Which of the following methods can be used to get rid of mycoplasma bacteria in cell cultures?
Either of these
Sterile filtering through 0.22 um pore filter
Neither of these
Penicillin antibiotics - ANS ✔✔Neither of these. notice it doesn't care about pore size, and has
no cell wall to be acted upon.
NOTE: air filters on flask also 0.22 um
Incubators - ANS ✔✔37 * Celcius (normal human body temperature). bottom water tray =
humidity > 90%. filled with water before it all evaporates, checked periodically to prevent drying
out.
high pressure gas tanks = 5% CO2 to maintain physiological pH 7.4 with bicarbonate buffers in
the media.
Built in sterilization cycle: moist heat at 90 degrees Celsius for 24 hours, run periodically.
Incubator shelves & interior parts should be disinfected with ethanol before sterilization cycle.
HEPA filter attempts to remove bacterial contamination.
When accessing the incubator, spray hands/all flasks with ethanol
Biological safety cabinet (BSC) - ANS ✔✔vertical laminar flow hoods (air flow pattern inside the
hood is non-turbulent); air flowing down from ceiling of cabinet, horizontal = air blowing from
Practice Questions & Answers)
Steam sterilization (autoclave) - ANS ✔✔Usually 30 minutes at 121 degrees C; Most widely used
and most dependable; Heat compatible:
OK - polypropylene, silicone, metals
Not OK - polystyrene, polyethylene’s
polypropylene - ANS ✔✔conical tubes, microcentrifuge tubes, micropipette tips
polystyrene - ANS ✔✔all of our tissue culture flasks, well plates, serological pipettes; cell
culture: treat w/plasma = less hydrophobic, fibronectin adsorb/cells attach
Ethylene oxide (gas phase sterilization) - ANS ✔✔sterilizing items sensitive to heat;
Residue harmful, aeration to remove residue.
Ionizing radiation (gamma radiation) - ANS ✔✔Provides good penetration, but sometimes
damage surfaces of materials; High cost/not used in health care facilities; Large scale production
(all the conical tubes and flasks, including T75 for tissue culture)
Peracetic acid
Liquid - ANS ✔✔Sterilize equipment with narrow long lumens; endoscopes
Dry heat (oven) - ANS ✔✔autoclave no steam;
Much higher temperatures, longer time; powders if they are not susceptible to heat
Filter sterilization - ANS ✔✔Physically remove particles. ex:
,0.22 um pore filter
Useful for heat sensitive liquids
Ultraviolet light - ANS ✔✔Directional:cannot sterilize surfaces that aren't illuminated.
Poor penetration - UV light does not go through much
Not FDA approved
Lab disinfectants - ANS ✔✔70% Ethanol (more effective than 100%), 10% Sodium hypochloride
(bleach) for mammalian cells; eventually goes bad from light and heat. bad ~ week
Other disinfectants - ANS ✔✔Hydrogen peroxide (3%), Iodine, Phenol, Lysol (quarternary
ammonium compounds)
Disinfection vs. Sterilization - ANS ✔✔•* Disinfection *= Destroying PATHOGENIC microbes
except for spores (ie chemical disinfection, pasteurization)
•* Sterilization *= Killing ALL microbes (good & bad) (ie autoclave, flash sterilization, low temp
sterilization)
in lab words: disinfection is less effective sterilization. Keep the outside of things clean
We sterilize our hands with 70% ethanol before touching anything inside the biological safety
cabinet. - ANS ✔✔False! Disinfect!
Mycoplasma - ANS ✔✔Preventing mycoplasma contamination is difficult. For one, mycoplasma
cells are small (0.3-0.8 µM in diameter) and pleomorphic (8), allowing them to pass through
standard filtration membranes. Secondly, mycoplasmas lack cell walls. This makes them
impervious to cell culture antibiotics that inhibit cell wall synthesis, such as penicillin. Effective
antibiotics do exist, however, their continuous use in cell culture is not recommended due to
, possible cytotoxicity. Third, mycoplasmas are able to reach high concentrations in the media of
infected cells without noticeable turbidity (9). This makes detection via visual inspection
difficult. Lastly, while the primary source of mycoplasma contamination is likely other cell
cultures, mycoplasmas from lab personnel are a potential source as well (7). Hence, the only
reliable ways to minimize contamination are to test routinely (and frequently), practice safe cell
culture techniques and to obtain cells from reputable sources such as the American Type
Culture Collection (ATCC).
Which of the following methods can be used to get rid of mycoplasma bacteria in cell cultures?
Either of these
Sterile filtering through 0.22 um pore filter
Neither of these
Penicillin antibiotics - ANS ✔✔Neither of these. notice it doesn't care about pore size, and has
no cell wall to be acted upon.
NOTE: air filters on flask also 0.22 um
Incubators - ANS ✔✔37 * Celcius (normal human body temperature). bottom water tray =
humidity > 90%. filled with water before it all evaporates, checked periodically to prevent drying
out.
high pressure gas tanks = 5% CO2 to maintain physiological pH 7.4 with bicarbonate buffers in
the media.
Built in sterilization cycle: moist heat at 90 degrees Celsius for 24 hours, run periodically.
Incubator shelves & interior parts should be disinfected with ethanol before sterilization cycle.
HEPA filter attempts to remove bacterial contamination.
When accessing the incubator, spray hands/all flasks with ethanol
Biological safety cabinet (BSC) - ANS ✔✔vertical laminar flow hoods (air flow pattern inside the
hood is non-turbulent); air flowing down from ceiling of cabinet, horizontal = air blowing from
