Lab 21 - Physical methods of control (heat) Flashcards
how do bacteria survive in hot environments?
-Rigid thermostable proteins (tightly folded to prevent denaturation)
-Rigid membranes (tightly packed lipids)
high temperatures are usually ____ and low temperatures are usually _____
high temperatures are usually bactericidal (bacterial killing) and low temperatures are usually bacteriostatic (bacterial growth stopped)
what is the #1 physical method of control if available?
heat
what does heat do?
it denatures proteins and destroys cell componenents
what are examples of heat physically controlling growth?
-Dry heat: flaming, incineration, dry heat ovens
-Moist heat: boiling 5-10 min, pasteurization, autoclave (pressurized steam)
what is the preferred method of sterilization for surgical and medical equipment, media, and glassware, if it is available?
autoclave
what in an autoclave kills the endospores?
the heat not the pressure
what is one standard protocol for autoclaving?
121 degrees celsius at 15 psi for 15 minutes - it destroys endospores
what was the difference between B. subtilis at 24 hours vs 48 hours?
the amount of time it was cultured. the 48 hour B. subtilis runs out of food to eat, so it creates endospores. it is harder to kill
E. coli at 72 degrees: what is its growth?
0’: +++
0.5’: +++
2’: ++
5’: NG
15’: NG
S. epidermidis at 72 degrees: what is its growth?
0’: ++++
0.5’: +++
2’: ++
5’: NG
15’: NG
S. epidermidis at 63 degrees: what is its growth?
0’: ++++
0.5’: +++
2’: ++
5’: +
15’: NG
B. subtilis 24hr at 72 degrees: what is its growth?
0’: +++
0.5’: NG
2’: NG
5’: NG
15’: NG
B. subtilis 24hr at 63 degrees: what is its growth?
0’: +++
0.5’: ++
2’: NG
5’: NG
15’: NG
B. subtilis 48hr at 72 degrees: what is its growth?
0’: +
0.5’: ++
2’: ++
5’: +++
15’: ++++
