Chapter 9- Controlling Microbial Growth Flashcards
Static
inhibits growth but does not kill the microbe
Cidal
kills the microbe
Sterilization
The removal of all microorganisms, including endospores
Disinfection
A chemical treatment to kill/inhibit growth on inanimate objects
Degerming
The mechanical removal of most of the microorganisms in a limited area by scrubbing
Sanitation
Reducing the # of pathogens
Aseptic
Free of contamination
2 ways the microbial control agents kill or inhibit the growth of microorganisms:
- Alteration of cell walls/plasma membrane
- Damaging proteins/DNA
Alteration of cell walls/plasma membrane:
Disrupts osmosis and/or allows cellular contents to leak out
Damaging proteins/DNA
Denatures the shape of proteins
Factors to select the most appropriate antimicrobial:
- Harmless to humans
- Effectiveness
- Susceptibility of microbe (the bacteria must be susceptible to it)
Physical Methods of Microbial control
- Moist Heat
- Dry Heat
- Low Temperature
- Desiccation
- Filtration
- Osmotic Pressure
- Radiation
Moist Heat
Denatures proteins and disrupts cell membranes
Methods within moist heat
- Boiling
- Autoclaving
- Pastureization
Boiling
- Type of moist heat sterilization
- Kill pathogens and almost all viruses in 10 min
- Less effective on destroying endospores
At sea level, water boils at
100 C
Autoclaving
- Uses pressure per square inch (psi)
- Used to sterilized culture media and surgical equipment
- Gets rid of endospores
Pasteurization
- Kills pathogenic bacteria and most nonpathogens
- Many heat-resistant bacteria survive pasteurization but are nonpathogenic
- NOT sterilization
Dry Heat
Requires higher temps for often longer time periods compared to moist heat
Types of dry heat:
- Direct Flaming
- Hot-air Sterilization
- Incinerator
Direct Flaming
- Used to sterilize inoculating loops and needles
- ex: bunsen burner
The Bunsen burner achieves a temp of
1500 C
Hot-air Sterilization
- Placed in oven for 2 hours
- Used to sterilize empty glassware
Incinerator
Can achieve temperatures of 850C for as little as 2 seconds
Low Temperature
& important exception
- Refrigeration temperatures will slow bacterial growth and metabolism
- Bacteriostatic effect (will not kill, only inhibit)
Important exception: Listeria monocytogenes
Desiccation
- Condition where microorganisms cannot grow/reproduce in the absence of water
- When water is available again, they can resume their growth
- Bacteriostatic (will not kill, only inhibits)
- Lyophylization
Lyophilization
(freeze-drying), used for long-term preservation of microbial cultures
Filtration
- Removal of microorganisms by passage through pores
- Pores need to be small enough to hold back microbes
- Purpose of wearing face masks during surgery and for HEPA filters
Osmotic Pressure
- High concentration of salt and sugar in food to inhibit growth
- Microbial cells in hypertonic solution lose water and cannot grow/multiply
Radiation: two types
Ionizing radiation
Nonionizing radiation
Ionizing radiation
- Ejects electrons
- Creates hydroxyl radicals
- Good for controlling growth on gloves, syringes, meat/food
Nonionizing radiation
- Excites electrons
- UV light damages the DNA
- Good for surface objects
The mechanism of action for both types of radiation is the
damage to DNA
Chemical Methods of Microbial control and types
- Phenolics
- Halogens
- Alcohols
- Heavy Metals
- Surfactants
- Oxidizing Agents
Phenolics
- Denatures proteins and disrupts the cell membranes
- Triclosan: phenol and phenolics
- Found in garbage and diapers
Halogens
- Damages proteins with denaturation
- Iodine (oldest/most effective antispetic)
- Chlorine (disinfects water, present in bleach)
- Flouride (toothpaste)
- Bromine (hot tubs)
Alcohols
- Kill bacteria and fungi but not endospores
- Denatures proteins and disrupts plasma membrane
Heavy Metals
- Denatures proteins
- Exs: Zinc, Mercury, Copper, Silver
____ is often found in ___ creams
Silver is often found in burn creams
Surfactants-3 types
Soap
Acid-anionic detergents
Cationic detergents
Surfactants-mechanism of action
Disrupts cell membrane
Soap
- Good degerming agents
- Doesn’t really kill/inhibit growth
Acid-anionic detergents
- Carries negative charge
- Nontoxic and non-corrosive to humans
- Fast-acting
- Found in laundry detergent
Cationic detergents
- Carries positive charge
- Most widely used cationic detergents are Quats, which disrupt the cell membrane and is bacteriocidal except for endospores
Other than endospores, what else can Quats not destroy and why?
Mycobacteria due to the waxy cell membrane
Oxidizing Agents
- Damages cellular components of microbe
- Ex: Hydrogen peroxide
Hydrogen peroxide
- Not a good antiseptic for open wounds due to the enzyme catalase
- Good disinfectant for nonliving objects
