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The process of destroying all living organisms and viruses. A sterile object is one free of all life forms, including bacterial endospores, as well as viruses.
The elimination of harmful microoganisms from inanimate objects or surfaces.
An agent that is static in action will inhibit growth of microorganisms.
An agent that is cidal in action will kill microorganisms and viruses.
Is moist or dry heat more effective in controlling microorganisms? Why or why not?
Moist heat is more effective because of its ability to penetrate microbial cells.
State 2 methods of applying moist heat.
Describe the process of autoclaving (pressure, time, and temp.).
Autoclaving employs steam under pressure. Under pressure the boiling point of water increases. When a pressure of 15lbs./in2 is applied the boiling point of water increase from 100oC to 121oC. Generally 15-45 minutes is cidal for both organisms and endospores.
Is boiling and effective means of sterilization? Why or why not?
Boiling is not an effective means of sterilization. Although it will kill vegetative cells after 10 minutes of exposure, certain viruses may survive after 30 minutes of exposure and endospores may survive after hours of boiling.
State 2 methods of applying dry heat.
- Hot air sterilization
- The mild heating of milk and other material to kill particular spoilage organisms or pathogens.
- 71.6oC for 15 seconds (flash method)
- 62.9oC for 30 minutes (holding method)
Does low temperatures have a static or cidal effect on microorganisms? Why?
Low temperatures have a static effect on microorganisms because is only slows down microbial metabolism and inhibits growth.
Does desiccation have a static or cidal effect on microorganisms?
Desiccation has a static effect on microorganisms.
How does desiccation affect the cell?
The lack of water inhibits the action of microbial enzymes. Dehydrated foods do not require refrigeration because the absence of water inhibits microbial growth.
Describe osmosis in terms of water flow through a semi-permeable membrane.
Osmosis it the flow of water through a semi-permeable membrane through a concentration gradient. The water flows from greater water concentration to lower water concentration.
Define hypertonic as it relates to microbes.
If the concentration of water inside a cell is greater than the concentration of water outside the cell; the cell is in a hypertonic environment.
If cell is placed in a hypertonic environment the cell will begin to lose water to the enviroment causing the shrinkage of the cytoplasmic membrane. The cell becomes dehydrated and growth is inhibited.
Described how bacterial growth is inhibited in jams and in salt-cured meats.
In both cases bacteria are placed in hypertonic conditions (high sugar concentration in jams, and high salt concentrations in cured meats) causing plasmolysis of the microorganism's cell.
Why must jams still be sealed although bacteria will not grow in them.
Although bacteria will not grow in jams because of plasmolysis, molds, however, will. If fact mold will use the sugars of the jam and to flourish. Molds are aerobic, sealing the jam will creates and anaerobic environment.
Does hypertonicity have a static or cidal effect on microorganisms?
It has a static effect on microorganisms.
How does the wavelength and the length of exposure influence the bacteriocidal effect of UV light?
- The most cidal wavelength of UV light is 260-270nm, where it is absorbed by nucleic acid.
- The longer the exposure to UV light the greater the cidal activity.
How does UV light kill microorganisms? (Thymine dimer)
- UV light is absorbed my microorganism.
- Adjacent thymine bases bond together forming thymine-thymine dimers.
- During replication complementary bases do not pair with the thymine dimer and terminates replication.
How does UV light kill microorganisms? (SOS repair)
- Heavily damaged DNA with large numbers of thymine dimers, a process called SOS repair is activated as a last ditch effort.
- Gene product of the SOS system binds to DNA polymerase allowing synthesis across damaged DNA.
- Altered DNA polymerase looses its proof-reading ability.
- Resulting in the synthesis of DNA that itself contains many misincorporated bases.
- Summary: UV radiation causes mutation and is called a mutagen.
Why is UV light only useful as a means of controlling surface contaminants? Give practical examples.
- UV light has very poor penetrating power.
- Examples: hospital operating rooms and sinks, aseptic filling rooms of pharmeceutical companies, microbiological hoods, processing equipment used by food and dairy industries
State the concept behind sterilizing solutions with micropore membrane filters.
- The filter contains pores small enough to prevent the passage of microbes but large enough for fluids to pass through.
- Filters with pore diameter from 25nm to 0.45μm are used.
Why are filters preferred over autoclaving for such materials as vaccines, antibiotic solutions, sera, and enzyme solutions?
Use in sterilizing materials such as vaccines, antibiotic solutions, animal sera, enzyme solutions, vitamin solutions, and others that may be damaged or denatured by high temperatures or chemical agents.
Substances produced as metabolic products of one microorganism which inhibit or kill other microorganisms.
Define antimicrobial chemotherapeutic chemical.
Chemicals synthesized in the laboratory which can be used therapeutically on microorganisms.
Define narrow spectrum antibiotic.
Antibiotics that are effective on just G+ bacteria, just G- bacteria, or only a few species of bacteria. (penicillin G, erythromycin, clindamycin, gentamicin)
Define broad spectrum antibiotic.
Antibiotics that are effective againsts a variety of both G+ and G- bacteria. (tetracycline, streptomycin, cephalosporins, ampicillin, sulfonamides)
What is meant by selective toxicity in terms of antimicrobial chemotherapy?
The agent (antibiotic or chemical) used must inhibit or kill the microorganism in question without seriously harming the host.
State why antimicrobial susceptibility testing is often essential in choosing the proper chemotherapeutic agent to use in treating and infection.
For some microorganisms, susceptibility to chemotherapeutic agents is predictable. For many other microorganisms (Pseudomonas, Staphylococcus aureus, G- enteric bacilli like E. coli, Serratia, Proteus, etc.) there is no reliable way of predicting which antimicrobial agent will be effective, especially with the emergence of antibiotic-resistant strains of bacteria. Because of this antimicrobial susceptibility testing is essential to determine which antimicrobial agent to use against a specific strain of bacterium.
- Unicellular eukaryotic microorganisms belonging to the Kingdom Protista.
- Reproduce asexually by fission, schizogony, or budding. Some also reproduce sexually.
THe vegetative form (motile, feeding, reproducing form) of a protozoan.
A protective form of a protozoan that enables them to survive harsh conditions.
What causes the recurring fever of malaria?
It is the result of the lysis of the infected red blood cells, causing release of merozoites and their metabolic by-products.
What disease does Entamoeba histolytica cause?
- amoebic dysentary
- Note one or more nuclei.
What disease does Trypanosoma gabiense cause? (Tsetse fly)
- African Sleeping sickness
- Note nucleus, flagellum, and undulating membrane.
What disease does Giardia lamblia cause?
- Note the two nuclei resembling "eyes."
What disease does Trichomonas vaginalis cause?
- genitourinary trichomoniasis, vaginitis
- Note large nucleus, flagella, and undulating membrane.
What disease does Balantidium coli cause?
- Note large "dumbell-shaped" macronucleus (arrow).
What disease does Plasmodium cause?
Multicellular, macroscopic worms having both rudimentary organs and organ systems.
eggs of helminths
Individual containing both male and female sexual organs.
List 3 classes of parasitic helminths and the common name for each class.
- Nematodes (Roundworms)
- Cestodes (Tapeworms)
- Trematodes (Flukes)
State how ascariasis is transmitted to humans and how it is diagnosed in the clinical laboratory.
- Ingestion of water or food contanimated with feces that contain Ascaris ova or from fingers contaminated with polluted soil.
- Microscopically looking for Ascaris ova in a fecal smear.
State how pinworms are transmitted to humans and how it is diagnosed in the clinical laboratory.
- Inhalation of E.vermicularis ova or from transfer of ova to the mouth from fecally-contaminated fingers.
- Applying tape to the perianal region and microscopically looking for pinworm ova that have stuck to the tape.
State how trichinosis is transmitted to humans and how it is diagnosed in the clinical laboratory.
- By eating poorly cooked infected pork.
- Serological tests and microscopic examination of biopsy specimens.
State how tapeworms are transmitted to humans and how it is diagnosed in the clinical laboratory.
- By eating poorly cooked infected beef, pork, or fish containing cysticerci.
- Looking for proglottids and ova in the feces.
State how flukes are transmitted to humans and how it is diagnosed in the clinical laboratory.
- By ingesting poorly cooked fish, crayfish, crabs, snails, or water vegetables infested with flukes.
- (diagnosis was not stated in lab manual)
Anterior end of Ascaris
lumbricoides showing mouth, esophagus, and intestine.
Ova of Ascaris lumbricoides.
Note "serrated edge" of ova (arrows).
Ova of Enterobius
vermicularis. Note "smooth edge" of ova (arrows).
in muscle tissue.
Note spiraled larva of
Trichinella (arrow) encysted in the muscle.
Note the attachment structure or scolex, immature, mature, and gravid
Scolex of a tapeworm
Note hooks and suckers for attachment to intestinal wall.
Ova and uterus in gravid proglottid of a tapeworm.
The gravid proglottids are basically segments containing a uterus filled with
ova and a genital pore for release of ova.