Module 4: Physical and Chemical Growth Control Flashcards
5 Methods of Controlling Microbial Growth (Physical and Chemical)
- Heat Sterilization
- Pasteurization
- Radiation
- Filtration
- Chemicals
Decontamination Definition
Inhibit the growth of microbes
-cidal : kill
-static : inhibits
Decimal Reduction Time (D)
Time required at a given temperature for a tenfold reduction in the viability of a microbial population
Thermal Death Time (TDT)
Time it takes to kill all cells at a given temperature
4 Factors affecting Thermal Death Time
- Presence of endospore forming bacteria
- Medium in which heating takes place
- Concentration of sugars proteins and fats
- Concentration of salt
Two molecules present in endospores that improve heat stability
- Dipicolinic Acid (Ca+ complex)
- Small-acid Soluble Proteins (SASP)
D(endospore)
D(vegetative)
Time and temperature to reach 1/10th *
D(endospore) - 4-5 mins @ 121 degrees celsius
D(vegetative) - 0.1-0.5 @ 65 degrees celsius
Dry Heat vs Moist Heat
DRY HEAT
- slow heat and steam production
- sterilizes glasswear
- flame sterilization
- hot or correction areas
- 160-120 degrees celsius for 1-16 hours
MOIST HEAT
- higher heat and steam production
- produces faster D
- Autoclaves
- 121 degrees celsius, for 15 Psi, for 15-20 minutes
Autoclave conditions
20-30 minutes
121 degrees celsius
15 Psi
3 Types of Pasteurization
- Flash Pasteurization
- controlled milk flow rate
- 71 degrees for 15s - Holding Pasteurization
- not palatable for most consumers
- 62 degrees for 30mins - Ultrahigh Temperature
- 74 degrees –> 140 degrees –> 74 degrees for <5s
4 Types of Low temperatures
- Refrigeration
- ~5 degrees - Freezing
- ~-20 degrees - Drying
- absence of water inhibits enzymatic activities - Freeze-Drying
- LYOPHILIZATION: process in which water in the form of ice under low pressure is removed from a material by sublimation
2 Types of Radiation
- Ultraviolet light
- 220-300nm
- causes breaks and modifications in DNA resulting in cell death
- may become ineffective because of activated repair mechanisms
- limited to disinfecting exposed surfaces - Ionizing Radiation
- X-rays & gamma rays
- highly reactive molecules that can destroy DNA, lipids and proteins resulting in cell death
- measured in ROENTGEN (radiation absorbed per g of tissue)
LYOPHILIZATION
: process in which water in the form of ice under low pressure is removed from a material by sublimation
2 Types of Filtration
- Depth Filters
- fibrous sheath of randomly overlapping paper or borosilicate fibers
- HEPA filters - Membrane Filters
- most commonly used in liquid sterilization
- high tensile strength polymers
- syringe + pump + collecting vessel
—> NUCLEATION TRACK/NUCLEOPORE: uniformly-sized pores; isolate specimen for SEM
3 types of Chemical Growth Rate Control
- Bacteriostatic
- inhibitors of protein synthesis
- viable and total cells are the same - Bactericidal
- binds to cellular target; kills it
- viable cell count is lower than total cell count - Bacteriolytic
- kills cells via cell lysis
- viable and total cells are the same (but both decreasing)
Measuring Antimicrobial Activity (2)
- Disc Diffusion Technique
(i) inoculate plate w/ test organisms
(ii) discs containing antimicrobial agents are placed on surface
(iii) test organisms demonstrates “zone of inhibition” - Minimum Inhibitory Concentration
- tube dilation technique
- smallest amount of agent to inhibit microbial growth (clear test tube)
4 Factors affecting MIC
- Bacterial species
- Inoculum size
- Culture medium
- Incubation conditions
Antiseptics & Germicides
Nontoxic agents that can kill/inhibit growth of organisms; LIVING TISSUE
Disinfectants
Kills organisms; INANIMATE ORGANISMS
Sanitizers
Reduces microbial numbers
Sterilant
Destroy all forms of microorganisms
PHENOLS & PHENOLICS
- antiseptic
- mode of action:
i) disrupts cytoplasmic membrane
ii) denatures DNA
iii) inactivates enzyme - soaps, lotions, cosmetics, body deodorant
HALOGENS
- sterilant, disinfectant, sanitizer
- modes of action:
i) iodine binds to tyrosine residues of proteins; inhibits protein production
ii) iodine oxidizes sulfhydryl groups; disrupts protein structure
iii) Water + Cl = oxidizing agent (hypocholorous acid) - topical antiseptic, disinfectant of lab surfaces
ALCOHOLS
-antiseptic (@70%)
- Mode of actions
i) denatures proteins (w/ water)
ii) disrupts cellular membrane
iii) lipid solvent
- topical antiseptic
Quaternary Ammonium Compounds
- Disinfectant, antiseptic, sanitizer
- Mode of actions:
i) disrupts the membrane
ii) interacts with phospholipids - medical food and dairy equipment; soaps lotion topical disinfectant
- support the growth of Psuedomonas sp.
ALKYLATING AGENTS
- disinfectant, sterilant
- Modes of action:
i) disrupts proteins and structure of nucleic acids - surface disinfectant, sterilant for temp-sensitive materials (plastics); high level disinfectant for medical instruments
OXIDIZING AGENTS
- antiseptic, disinfectant, sterilant
- Modes of action:
i) membrane and protein stability