Exam 2 deck 1 Flashcards
Sepsis
Bacterial contamination
3 ways to control microbial growth
1) Physical and chemical methods
2) Chemotherapeutic drugs
3) Immune system and vaccines
Disinfection
Destroys microbes on inanimate object –> only kills harmful microbes
Antiseptic
Chemical disinfection of living tissue
e.g. iodine
Sterilization
kills all forms of microbes, including endospores and viruses
Germicide
Chemical agent that kills microbes, but not necessarily endospores
Bacteriostatic microbial suppression
stops growth, but doesn’t kill
Bactericidal microbial suppression
kills microbes
What affects the rate of microbial death?
1) the number of microbes
2) Temperature (disinfectants’ work increases at higher temps, but microbes grow slower at lower temps)
3) Type of microbe (vegetative cells are least resistant)
4) Physiological state of microbe (cells in “log” phase are most succeptible)
5) cell environment (organic matter could offer protection)
How does heat control microbial growth?
It denatures the enzymes in the microbes
Thermal Death Point
lowest temperature at which all cells in a liquid culture will be killed within 10 minutes
Thermal Death Time
Minimum time for all bacteria in a liquid culture to be killed at a particular temperature
Decimal Reduction Time
Minutes to kill 90% of a specific population of bacteria at a given temperature
Moist Heat Examples
Boiling
Free flowing steam
Pressurized steam (autoclave)
How does boiling/ free flowing steam affect microbes?
Disinfects, but doesn’t sterilize
How does pressurized steam affect microbes?
It sterilizes
- at 15 psi the steam reaches 121 C
- 15 minutes will kill all organisms and spores
- the pressure prevents the liquid from boiling
What is a word for low heat treatment?
Pasteurization
Explain High-Temp Short-Time and Ultra-High-Temp
HTST is 72 C for 15 seconds
UHT is 140 C for 4 seconds
What kind of organisms can survive pasteurization?
Thermoduric organisms
What happens chemically when something burns?
It is oxidized
3 types of dry heat
Flaming, incineration, and hot air sterilization
Filtration
- Passage of substance through scree-like filter
- used for heat-sensitive materials
- we want the liquid, not the microbes
What kind of affect does low temperature have on microbes? Which microbes are immune to this?
It has a bacteriostatic affect and psychrotrophs are immune
What affect does high pressure have on microbes?
It denatures proteins
What does desiccation do?
Lack of water prevents metabolism
usually makes bacteria dormant, but doesn’t kill them
What does osmotic pressure do?
It creates a hypertonic environment, causing plasmolysis. This prevents the bacteria from replicating
3 Types of radiation
Ionizing, non-ionizing, and microwaves
Ionizing radiation
- ionizes water to make reactive hydroxyl radicals
- Damages DNA by causing lethal mutations which prevent the cell from making necessary enzymes
Non-ionizing radiation
- Creates thymine dimers
- polymerase can’t do its job, so DNA is not transcribed
Microwaves
kill by heat, but not especially antimicrobial
