Exam 2: Controlling Microbial Growth in the Environment Flashcards
Antisepsis
Use of physical or chemical agents to inhibit or destroy microorganisms on skin or other tissues. The items used are called Antiseptics. Commonly uses the same chemicals present in disinfectants but often at lower concentrations.
Aseptic
free of contamination by pathogens. Does not mean no microbes can be transferred but the number of microbes potentially transferred is very low. e.g. Aseptic packaging of food or aseptic lab technique.
Degerming
Removal of microbes from a surface by scrubbing. e.g. Hand washing. Chemicals may be used but the action of scrubbing is more important.
Disinfection
Use of physical or chemical agents to inhibit or destroy microorganisms on inanimate objects. e.g. Alcohol, bleach, heat, ultraviolet light.
Pasteurization
Use of heat to kill pathogens and reduce the number of spoilage microorganisms. e.g. Milk, fruit juices, beer, and wine are commonly pasteurized.
Preservation
Delays the spoilage of food or other perishable items. Slows bacterial growth but does not kill them “bacteriostatic”. e.g Adjustment of storage conditions or addition of chemical preservatives.
Sanitization
Disinfecting places and utensils used by the public. Reduces the number of pathogenic microbes to meet accepted public health standards. e.g. pressurized hot water, chemicals used to sanitize public toilets. Distinction is dishes are disinfected at home and sanitized at a resturant.
Sterilization
The removal or destruction of all microorganisms. Includes viruses and endospores.
Define and contrast bactericidal and bacteriostatic
Bactericidal destroy or permanently inactivate amicrobe while bacteriostatic inhibit microbial metabolism and growth. Bleach vs. refrigeration.
Define and contrast fungicidal and fungistatic
Kill fungi vs. inhibit fungi metabolism and growth
Define and contrast germicidal and germistatic
Kill germs vs. inhibit germ metabolism and growth
Give three specific examples of the undesirable growth of microorganisms.
1) Food spoilage
2) Medical procedures and surgery
3) Shared public surfaces/ spaces
What is a microbial death rate? Does it generally vary over time? Does it generally vary between species? Does it generally vary under different conditions? Explain.
Rate at which some microbes are killed (permanent loss of the ability to reproduce), generally constant over time (specific to a particular microorganism and set of conditions), useful to determine the efficiency of antimicrobial agents.
A constant percentage is killed each minute, specific to a particular microbe under a particular set of conditions. Number of dying per minute is not constant as most susceptible die first, smaller population is left, most susceptible of reminder die next, etc.
In what way is knowing a microbial death rate useful?
Useful to determine the efficiency of antimicrobial agents and how long those agents need to be used to thoroughly kill specific microbes.
What cellular features are generally disrupted by microbial control agents?
1) Disruption of the cell intregrity by altering the cell wall or cytoplasm.
2) Interruption of cellular metabolism and reproduction by interfering with protein or nucleic acid structue.
Doe does disruption of the cell integrity by altering the cell wall or cytoplasm affect the cell or virus?
Cell wall manages osmotic protection and damage causes an influx of water bursting the cell.
Cytoplasmic membrane regulates movement of molecules into/out of the cell, damage can cause cellular content to leak out.
Viral envelope is a membrane, damage prevents viral attachment to host and thus interferes with viral entry.
How does interruption of cellular metabolism and reproduction by interfering with protein or nucleic acid structure affect the cell or virus?
Protein function is dependent upon its structure, extreme heat and chemicals can denature the proteins.
Genes and gene expression depend upon the integrity of nucleic acids, chemicals/radiation/heat can alter or destroy nucleic acids. Results in gene mutations that can be damaging or lethal. Inactivation of the ribozyme core of ribosomes can halt protein synthesis.
What are the key characteristics of an ideal microbial control agent?
Inexpensive
Fast-acting
Stable
Not harmful to humans, animals, and objects.
Is there a single “best” microbial control agent? Explain.
No, all agents have limitations and disadvantages. Might not meet all the key characteristics or might partially only meet all of them. The “best” is going to depend on needs and conditions.
What key factors should be considered when selecting a microbial control method for a given application? Explain.
1) Nature of the sites to be treated. Many objects cannot withstand harsh chemicals or extreme heat.
2) Degree of susceptibility of the microbes involved. Death rates vary significantly between microbes.
3) Relevant environmental conditions.
Should the same measures be taken to control microorganisms on all different types of medical equipment? Explain.
No, potential risk of infections must be considered. More rigorous procedures are necessary for items more likely to transmit infectious agents.
Critical items- direct contact with body tissues (needles, scalpels), sterilization necessary. Semi-critical items- have contact with mucous membranes (endoscope, speculum). Non-critical items- have contact with unbroken skin (stethoscope, BP Cuff).
Are all microorganisms equally sensitive to a given microbial agent? Explain. Talk about the levels of germicides.
No, some are easier to kill than others. Enveloped viruses are more sensitive than nonenveloped viruses. Endospores vs vegetative cells. Enveloped viruses are easiest to kill while Prions are hardest.
High-level germicides- Kill all pathogens, including bacterial endospores, used to sterilize invasive instruments. Can be chemical or physical like autoclaves. Intermediate-level germicides- Kill most pathogens but not bacterial endospores, used on noninvasive instruments that contact mucous membranes. Low-level germicides- Kill growing cells and some viruses, used to disinfect items that contact skin.
In what ways do temperature and pH typically effect microbial death rate?
Warm disinfectants work better than cool ones as chemicals react faster at higher temps. Extremely acidic or alkaline conditions increase death rate, chlorine bleach is more effective at acid pH.
In what ways do organic materials affect microbial death rate?
Interfere with the penetration of heat, chemicals, and some radiation. Essentially hid the bacteria. e.g. Fat, vomit, blood, intercellular secretions of biofilm. Objects should be cleaned prior to sterilization or disinfection.
What is the basis for defining the various biosafety levels?
Based on the hazard of the microbes to the human body.
The bacteria you are using in lab require a facility with which biosafety level?
BSL-2 is for handling moderately hazardous agents able to cause disease in humans
e.g., Staphylococcus aureus, HIV, etc.
Additional precautions include self-closing doors, wearing PPE, and autoclave decontamination of waste
Is the use of heat to control microbial growth a recent realization? Explain.
No, has been known long since the discovery of microbes. Goes back to the army of Alexander the great boiling water.
Is heat used to sterilize, to disinfect, or both? Explain.
Both denatures proteins, interferes with cell membrane and cell wall integrity, disrupts the structure of nucleic acids.
What is thermal death point? What is thermal death time?
Thermal death point: lowest temp that kills all cells in a broth in 10 minutes.
Thermal death time: time it takes to completely sterilize a particular volume of liquid at a set temp.
What is decimal reduction time? How can it be used to determine when ALL of the microbes in a sample have been killed?
Time it talks to kill 90% of microbes in a sample, percent killed per unit time is constant. Based on the largest amount of potential microbes can determine how long to heat a sample.
What cellular structures are damaged by moist heat?
Denatures proteins and destroys cell membranes, commonly used to sterilize and to disinfect. More effective than dry heat. Main methods are boiling and autoclaving.
Is boiling an effective means of achieving true sterilization? Explain.
No, boiling kills many types of cells within 10 minutes (vegetative, protozoa, and most viruses). However many types of cells can survive, endospores, protozoan cysts, and some non-enveloped bacteria.
Which groups of microbes are typically destroyed by ten minutes of boiling, and which groups can commonly survive such treatment?
Vegetative bacteria, vegetative fungi, trophozoites of protozoa, and most viruses killed. Endospores, cysts, and nonenveloped viruses survive.
What is the temperature of boiling water (at sea level)? What is the temperature of water in an autoclave? How is this possible?
100C is boiling while 121 C can be reached in the autoclave. Possible thanks to pressure and steam, steam is build up to 15psi and archives 121C.
Is autoclaving an effective means of achieving true sterilization? Explain.
Yes, true sterilization using heat requires temperatures higher than boiling water. Process verified with heat-sensitive indicator or endospore test ampule.
For what purpose was pasteurization initially developed?
Avoid wine spoilage, developed by Louis Pasteur.
Pasteurization is widely practiced; what are its key benefits?
Fast, Disinfects, Preferentially eliminates pathogens and spoilage organisms
Is pasteurization an effective means of achieving true sterilization? Explain.
No, its disinfection, preferentially eliminates pathogens and spillage organisms. Heat tolerant and endospores survive.
