Exam 2: Microbial control Flashcards
Antisepsis
The reduction in the number of microorganisms on living tissue
Aseptic
An environment or procedure free of pathogens
Degerming
The removal of microorganisms by mechanical means
Disinfection
The destruction of host microorganisms on non-living tissue
Pasteurization
The use of heat to destroy pathogens and reduce the number of spoilage microorganisms in food and beverages
Sanitization
The removal of pathogens from objects to meet public health standards
Sterilization
The destruction of all microorganisms in or on an object
Thermal death point
Lowest temperature that kills all cells in broth in 10 min
Thermal death time
Time taken to sterilize volume of liquid at set temperature
Decimal Reduction
Time required to destroy 90% of microbes in a sample
-cide meaning
suffix indicating that agent kills
include bactericides and everything else
-static meaning
suffix indicating that agent inhibits growth
include bacteriostatic and fungistatic
Discuss the significance of the selection criteria for microbial control agents
Ideally, agents should be:
Inexpensive
Fast-acting
Stable during storage
Capable of controlling microbial growth while being harmless to humans, animals, and objects
Describe factors that may affect the efficacy of antimicrobials
Physical & Environmental:
Temperature
- High Temps denature proteins & interfere with membrane fluidity. Heat can increase efficacy and activity
pH
- Changes in pH modify the ionization of functional groups and disrupt hydrogen bonding. This affects the stability of the agent
Susceptibility of microorganisms:
- Germicides classified as high, intermediate, or low effectiveness (most resistant to most susceptible)
- High-level kill all pathogens, including endospores
- Intermediate-level kill fungal spores, protozoan cysts, viruses, and pathogenic bacteria
- Low-level kill vegetative bacteria, fungi, protozoa, and some viruses
Differentiate between thermal death time and decimal reduction
Thermal death time: time to sterilize volume of liquid at set temperature
Decimal Reduction: time required to destroy 90% of microbes in a sample
Define the parameters for autoclaving and pasteurization
a. Autoclave
- Pressure applied to boiling water prevents steam from escaping
- Boiling temperature increases as pressure increases
- 121 C 15psi, 15 min
- Sterilizes
- Will kill endospores
b. Pasteurization
- Flash pasteurization: 72C – for 15 seconds
- Ultra High temp. Pasteurization: 138C – for 2 seconds
- Batch method: 63*C – for 30 minutes
Differentiate between biosafety levels
BSL - 1: nonpathogenic microbes
BSL - 2: Moderately hazardous agents (opportunistic)
BSL - 3: True pathogens
BSL - 4: Handling of microbes that cause severe or fatal disease
Describe the methods of microbial control discussed in lecture and explain the mechanisms behind their functions
review chart
Compare and contrast various physical methods and their mechanisms. (i.e. pasteurization vs.
autoclaving. Ionizing radiation vs. UV)
- Boiling:
Kills vegetative cells of bacteria, fungi, protozoan, trophozoites, and viruses
Boiling time is critical as different elevation require different boiling times
Endospores, protozoan cysts, and some viruses survive in boiling
-Autoclaving:
Pressure applied to boiling water prevents steam from escaping
Boiling temp increases as pressure increases
Sterilizes and will kill endospores
-Pasteurization:
Used for milk, ice cream, yogurt, and fruit juices
Used instead of boiling because boiling would affect taste
Heat tolerant microbes survive – not sterilization
Flash pasteurization used for extended shelf life
Ultrahigh-temperature sterilization
140*C for 1 second, then rapid cooling
Treated liquids can be stored at room temperature
Dry Heat:
Used for materials that cannot be sterilized with moist heat
Denatures proteins and oxidizes metabolic and structural chemicals
Requires higher temps for longer time than moist heat
Incineration is ultimate means of sterilization
Refrigeration and Freezing:
Decrease microbial metabolism, growth, and reproduction
Slower chemical reactions
Liquid water not available
Refrigeration halts growth of most pathogens
Psychrophilic microbes can multiply in refrigerated foods
Slow freezing more effective than quick freezing
Organisms vary in susceptibility to freezing
Filtering air:
Surgical masks
Cotton plugs on culture vessels
High efficiency particle air filters (HEPA)
Used in biological safety cabinets
Osmotic Pressure:
High concentrations of salt or sugar in foods to inhibit growth
Curing and Brining
Cells in hypertonic solution of salt or sugar lose water
Fungi have greater ability than bacteria to survive hypertonic environments
Non-ionizing Radiation:
Wavelength greater than 1nm
Excites electrons, causing them to make new covalent bonds (affects 3D structure of proteins and nucleic acids)
UV light causes pyrimidine dimers in DNA
UV light does not penetrate well
Suitable for disinfecting air, transparent fluids and surfaces of objects
Ionizing radiation:
Wavelengths shorter than 1nm (electron beams, gamma rays)
Ejects electrons from atoms to create ions
Ions disrupt hydrogen bonding, oxidize double covalent bonds and create hydroxide ions (denature DNA)
Electron beams (effective at killing but do not penetrate)
Gamma Rays (penetrate well but require hours to kill microbes)
Compare and contrast various Chemical methods of Microbial Control and their mechanisms
(PHOSHAA)
memorize chart