Microbiology Ch. 9 Flashcards
Discuss the historical roles played by Ignaz Semmelweis and Joseph Lister in preventing the spread of infection. (you will probably have to do a little Internet research to find out more information about these two men)
Ignaz Semmelweis:
Ignaz Semmelweis was the first doctor to discover the importance for medical professionals of hand washing. In the 19th century, it was common for women to die from an illness contracted during or after childbirth, known as childbed fever. While working at an obstetric department in Vienna, Austria, Semmelweis noticed that women delivered by physicians and medical students had a much higher mortality rate than women delivered by midwives. He concluded that the problem was that physicians were handling corpses during autopsies before attending to pregnant women, and determined that hand washing would prevent them from passing on illness.
Joseph Lister:
Antisepsis is the method of using chemicals, called antiseptics, to destroy the germs that cause infections. It was developed by the British surgeon Joseph Lister.
Photograph of Joseph Lister
Joseph Lister, 1827–1912.
Joseph Lister found a way to prevent infection in wounds during and after surgery.
He was the first to apply the science of Germ Theory to surgery.
Lister’s Antisepsis System is the basis of modern infection control.
His principles made surgery safe and continue to save countless lives.
sterilization
removing all microbial life (including viruses)
disinfection
Removing vegetative pathogens from inanimate surfaces. But not bacterial endospores. physical process or chemical agent
antisepsis
a growth-inhibiting agent used on tissues to prevent infection. Removing pathogens from living tissue. Reduces the number of microbes on the human skin. A form of decontamination but on living tissues.
Decontamination
sanitization
Bactericide
Is a chemical that destroys bacteria except for those in the endospore state. It may or may not be effective on other microbial groups.
germicide
An agent lethal to non-endospore-forming pathogens
Bacteriostasis
Agents that prevent the growth bacteria on tissues or on objects in the environment
sanitization
cleansing technique that mechanically removes microorganisms as well as other debris to reduce contamination to safe levels
Asepsis
a condition free of viable pathogenic microorganisms. Any practice that prevents the entry of infectious agents into sterile tissues and thus prevents infection.
Aseptic techniques: practiced in health care; range from sterile methods to antisepsis and disinfection.
Indicate the 4 main factors that determine how effective an antimicrobial control method is.
- Number of microbes
- Environment (organic matter, temperature, biofilms)
- Time of exposure
- Microbial characteristics
A. Some microbes have certain structural features that enable them to survive certain treatments
B. What is one feature you have learned about that enables a bacterial species to be heat tolerant.
Illustrate the hierarchy of microorganisms from those easiest to destroy to those most difficult to destroy (see figures in PowerPoint)
Prions
Bacterial endospores
mycobacterium
Protozoan trophozoites
most gram-negative bacteria
Fungi and fungal spores
nonenveloped viruses
Most gram-positive bacteria
enveloped viruses
(More resistant to least resistant)
Compare and contrast “cidal” and “static” microbial control processes
-cide (kill or destroy)
bactericides
Fungicides
virucides
sporicide
Microbicides (germicide)
cidal activity depends on use
-static (stop or stand still)
Bacteristatic
fungistatic
microbistatic
Describe the effects of microbial control agents on cellular structures. (Table 9.3 in text)
Cell wall: chemical agents can damage the cell wall by
-blocking its synthesis or
-digesting it
Examples: chemicals, detergents, alcohol.
Cytoplasmic membrane: agents disrupt the lipid layer of the cytoplasmic membrane. This opens up the cytoplasmic membrane and allows damaging chemicals to enter the cell and important ions to exit the cell.
Examples: detergents, alcohol.
Cellular synthesis: agents can interrupt the synthesis of proteins via the ribosomes, inhibiting proteins needed for growth and metabolism and preventing multiplication.
Examples: formaldehyde, radiation, ethylene oxide
Proteins: some agents are capable of denaturing proteins (breaking of protein bonds, which results in breakdown of the protein structure)
Agents may attach to the active site of a protein, preventing it from interacting with its chemical substrate.
examples: moist heat, alcohol, phenolics.
Compare the effectiveness of moist heat (boiling, autoclaving, pasteurization) and dry heat.
Moist heat can achieve the same effectiveness as dry heat but with lower temperatures and shorter exposure times. Although many cellular structures are damaged by moist heat, its most lethal effect is the coagulation and denaturation of proteins, which quickly and permanently halts cellular metabolism.
Dry heat dehydrates the cell, removing the water necessary for metabolic reactions, and it also denatures proteins. However, the lack of water actually increases the stability of some protein conformations, necessitating the use of higher temperatures when dry heat is employed as a method of microbial control. At very high temperatures, dry heat oxidizes cells, burning them to ashes. This method is the one used in the laboratory when a loop is flamed or in industry when medical waste is incinerated.
List several items that might be sterilized in an autoclave.
Glassware, cloth (surgical dressings), metallic instruments, liquids, paper, some media, and some heat-resistant plastics.
Indicate why the steam autoclave cannot be used to sterilize everything.
any material that has contacted volatile or corrosive chemicals, even normally compatible materials, should not be autoclaved. Radioactive materials and anything containing mutagens, teratogens, or carcinogens should never be loaded in an autoclave.
Indicate how you can be assured that an autoclave is working properly.
- Physical: pressure and temperature recording devices,
- Chemical: indicators that change color after being exposed to specific temperatures such as temperature sensitive tape. The color change upon exposure to the given temperature and
- Biological: Bacillus stearothermophilus spores are used, due to its resistance to heat, for the testing that measures the biological performance of the autoclave process.
List the 2 goals of pasteurization.
- Destroy/remove pathogenic microorganisms
- Extend the shelf life by reducing spoilage organisms
Compare pasteurization (classic and HTST) to UHT. What is accomplished by UHT that is not accomplished by either pasteurization method.
Classic pasteurization 71.6 degrees for 15 sec
Flash pasteurization: also known as high temperature short time (HTST) pasteurization. 63 degrees yo 66 degrees C for 30 min
Ultra-high temperature (UHT) pasteurization: Heat the milk to between 135°C to 140°C for 2 to 4 seconds. The treatment also destroys most of the microorganisms that cause spoilage and so prolongs the storage time of food. Ultra-high-temperature (UHT) pasteurization involves heating milk or cream to 138–150 °C (280–302 °F) for one or two seconds.
Define (equivalent treatments) and provide 2 examples.
- Classic pasteurization (batch)
63 C for 30 min - High-temperature short time (flash)
72 C for 15 sec.
Thermoduric organisms survive pasteurization
Pasteurization does not sterilize.
Ultra-high temperature (UHT) Treatment
140 C for < 1 sec
This technique actually sterilizes the product
dairy products treated with UHT can be stored in sealed containers at room temperature (this is NOT a type of pasteurization!!)
Describe how filtration, low temperatures, desiccation, and osmotic pressure suppress microbial growth.
Desiccation:
- vegetative cells directly exposed to normal room temperature gradually become dehydrated
- some microbes are killed by desiccation; many others are not killed and some are preserved
Lyophilization:
-combination of freezing and drying
-method of preserving microorganisms in a viable state for many years
-pure cultures are frozen instantaneously and exposed to a vacuum that removes water, avoiding the formation of ice crystals
Filtration:
-used to prepare liquids that cannot withstand heat such as serum, blood products, vaccines, drugs, IV fluids, enzymes, and milk. Alternative method for decontaminating milk and beer. Important step in water purification
-unable to remove soluble molecules (toxins) that cause disease
-high efficiency particulate air (HEPA) filters are used in hospital rooms and sterile rooms
Osmotic pressure:
-adding large amounts of salt or sugar to foods creates a hypertonic environment for bacteria, causing plasmolysis.
-pickling, smoking, and drying foods have been used for centuries to preserve foods
-never a sterilizing technique.
Know time/temp for steam autoclave, hot air sterilization, classic pasteurization, HTST pasteurization
Steam autoclave: 121 degrees C 15 psi 15 min
Hot air sterilization: 150 degrees C to 180 degrees C 2 to 4 hours
Classic pasteurization: 63 C for 30 min
High-temperature short-time: 72 C for 15 sec.
Indicate what sort of materials might be filter sterilized
Filtration is used to prepare liquids that cannot withstand heat, including serum and other blood products, vaccines, drugs, iv fluids, enzymes, and media. Is an alternative method for decontaminating milk and beer without altering their flavor. It is an important step in water purification.
Explain how radiation (ionizing radiation, as well as UV radiation) kills cells.
Ionizing radiation:
-highly effective alternative for sterilizing materials that are sensitive to heat or chemicals. Devices that emit ionizing rays include gamma-ray machines containing radioactive cobalt, x-ray machines similar to those used in medical diagnosis, and cathode ray machines. The dosage of radiation is measure in Grays.
Non ionizing radiation: Ultraviolet radiation ranges in wavelength from approximately 100 to 400 nm. It is most lethal from 240 to 280 nm (with a peak of 260 nm). Owing to its lower energy state, UV radiation is not as penetrating as ionizing radiation. Because uv radiation passes readily through air, slightly through liquids, and only poorly through solids, the object to be disinfected must be directly exposed to it for full effect.
Ultraviolet ray are a powerful tool for destroying fungal cells and spores, bacterial vegetative cells, protozoa, and viruses. Bacterial spores are about 10 times more resistant to radiation than are vegetative cells, but they can be killed by increasing the time of exposure. Even though it is possible to sterilize with uv, it is so technically challenging that we don’t regularly call it a sterilizing technology.
List appropriate applications of ionizing and UV radiation for sterilization.
Ionizing radiation:
-drugs, vaccines, medical instruments (especially plastics), syringes, surgical gloves, tissues such as bone and skin, and heart valves.
- causes formation of free radicals that damages DNA
Nonionizing radiation (UV, 260 nm)
-damages DNA by creating thymine dimers
UV radiation:
-hospital rooms, operating rooms, schools, food preparation areas, and dental offices
-proved effective in reducing postoperative infections, preventing the transmission of infections by respiratory droplets, and curtailing the growth of microbes in food-processing plants and slaughterhouses.
Identify a stretch of DNA that is susceptible to UV radiation damage.
UV radiation damages cells by causing the inappropriate formation of bonds between two adjacent bases on a DNA strand. It affects pyrimidines (Ts and Cs). If the new “dimers” are not repaired, they can prevent the segment of DNA from being correctly replicated or transcribed. Massive dimerization is lethal to cells.
List the factors influence the effectiveness of chemicals used for microbial control
Germicides are evaluated in terms of their effectiveness in destroying microbes in medical and dental settings:
-high level germicides kill endospores and can be used as sterilants
-intermediate level germicides kill fungal, but not bacterial spores, resistant pathogens, and viruses.
-low level germicides eliminate only vegetative bacteria, vegetative fungal cells, and some viruses
Factors:
-the nature of the material being treated
-the degree of contamination
-time of exposure
-strength and chemical action of the germicide
-microbial load
-concentration of disinfectant
-presence of organic matter (often interferes) cleaning must precede use of germicides
-pH
Describe the disk-diffusion method for testing the effectiveness of antiseptics and disinfectants.
The disk-diffusion method involves applying different chemicals to separate, sterile filter paper disks (Figure 13.4.1
). The disks are then placed on an agar plate that has been inoculated with the targeted bacterium and the chemicals diffuse out of the disks into the agar where the bacteria have been inoculated. As the “lawn” of bacteria grows, zones of inhibition of microbial growth are observed as clear areas around the disks. Although there are other factors that contribute to the sizes of zones of inhibition (e.g., whether the agent is water soluble and able to diffuse in the agar), larger zones typically correlate to increased inhibition effectiveness of the chemical agent. The diameter across each zone is measured in millimeters.
Identify preferred uses of the following chemicals: phenol, chlorhexidine, povidone iodine (Betadine), bleach and other chlorine compounds, alcohol, heavy metals (silver)
Phenol:
-targets some bacteria, viruses, fungi
-now only used in certain limited cases, such as drains, cesspools, and animal quarters
-banned in 2017 including triclosan and triclocarbon
Chlorhexidine:
- targets most bacteria, viruses, fungi
-mildness, low toxicity, and rapid action make chlorhexidine a popular choice of agents
-used in hand scrubs, prepping skin for surgery, as an obstetric antiseptic, as a mucous membrane irrigant, etc.
-effects on viruses and fungi are variable
Alcohol:
-most bacteria, viruses, fungi
-germicidal, nonirritating, and inexpensive
-routinely used as skin determine agents (70% to 95% solutions)
-rate of evaporation decreases effectiveness
-inhalation of vapors can affect the nervous system
Heavy metals (silver):
-some bacteria, viruses, fungi
-silver nitrate solutions are used for topical germicides and ointments
-may cause allergic reactions in susceptible individuals
Chlorine:
-can kill endospores (slowly) all other microbes
Less effective if exposed to light, alkaline pH, and excess organic matter
Povidone-Iodine:
-antiseptic used for skin disinfection before and after surgery
-minor wounds
-liquid or powder
Identify the appropriate uses for quaternary ammonium compounds and provide several examples
Their cationic nature makes them ideal as powerful cleaners. This makes them destroy most bacteria, some viruses, and fungi. They are stable and nontoxic.
examples: Benzalkonium chloride, alkyl dimethyl benzyl ammonium chloride. Found in hand soaps, toilet cleaners and disinfectant sprays, mouthwash
Describe appropriate uses of glutaraldehyde (cold sterilization)
-Can irreversibly disrupt the activity of enzymes and other proteins within the cell
-kills rapidly and is broad-spectrum; used to sterilize respiratory equipment, scopes, kidney dialysis machines, dental instruments
-somewhat unstable, especially with increased pH and temperature.
-virucidal in 10 min
-sporicidal in 3-10 hours
-formaldehyde
-ortho-phthaldehyde
Glutaraldehyde is used as a cold sterilant to disinfect and clean heat-sensitive equipment.
Identify chemical sterilizers
Alcohol, chlorine, formaldehyde, glutaraldehyde, ethylene oxide, plasma gas, iodine, phenolics, chlorhexidine, bisphenol, quats, silver.
