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Micro Lab Final Study Set
Terms in this set (186)
What does A/A refer to in a gram slant?
The reaction in regard to acid or alkaline. The reaction in the slant as well as *********** must be considered. A tube with an ACID BUTT + an ALKALINE SLANT= RED OVER YELLOW and will only ferment glucose, for example.
What would be seen in an acid butt gram slant with an acid slant?
Yellow over yellow. This will ferment glucose, lactose AND sucrose.
What would be seen in an alkaline slant and an acid butt?
Red over yellow. This will only ferment glucose.
What does it mean if both the butt and the slant are red or unchanged?
What is meant by A/black?
H2S formation (hydrogen sulfide). It contains iron.
What if bubbles are seen in a TSI slant?
These indicate gas production.
Do all Enterobacteriaceae ferment glucose?
How can glucose formation be used to differentiate members of the family if ALL Enterobacteriaceae ferment glucose?
All ferment carbohydrate glucose but not all can ferment sucrose and lactose. The TSI will determine the differences and make it possible to further identify the Enterobacteriaceae.
TSI slants are composed of more than one sugar. How would redesigning Simmon's citrate medium to include glucose and lactose impact the citrate test?
Some bacteria cannot grow with just sodium citrate as their source of carbon. If glucose and lactose are added this will allow some bacteria to grow and thus we are further able to differentiate.
You have narrowed the identification of an isolate down to two species, one of which ferments sucrose while the other does not. Because it contains sucrose, you consider using TSI to make this distinction and your final diagnosis. Is this a good solution to your problem? Explain.
Yes. The TSI slant will distinguish between those which can ferment sucrose and those who cannot and make this distinction clear. If the result is A/A the bacteria will ferment sucrose and lactose.
Characterize the color changes seen with phenol red, methyl red and bromthymol blue.
Phenol red is seen in the TSI as red when acid is oxidized to alkaline. Where acid remains it is yellow. The phenol red is used to distinguish acid from alkaline, and thus what can be fermented vs. what cannot. Methyl red is used in the V-P test as a pH indicator. It is red below 4.5 and yellow above. Only if it is red (a positive test) will we know the bacteria is capable of fermenting glucose. Bromthymol blue is used in the Citrate test. In this test bacteria that can use citrate as a carbon source will grow on the medium. To make the growth more visible the pH indicator bromthymol blue is in the medium. It will change from green to dark blue indicating growth and a positive test.
What accounts for over 90% of all urinary tract infections?
What are some properties of Enterobacteriaceae?
They are all gram-negative. They are all non-spore-forming. They are all facultative bacilli that reduce nitrate and are oxidase negative. They can all ferment glucose.
What are Enterobacteriaceae that ferment lactose to acid and gas within 24-48 hours called?
What are two examples of coliforms?
E. coli and Enterobacter
What are two of the most commonly used media for the isolation of enteric pathogens?
EMB and MacConkey MAC. Both contain lactose and are selective for gram negative bacilli.
What color colonies do bacteria that form lactose create? What color colonies do those that are nonfermenters create?
Lactose fermenters form dark colored colonies, for example E. coli. Nonfermenters such as Salmonella and Shigella form light colored colonies and these are the true pathogens.
This is an inorganic carbon-containing compound.
What does a positive Citrate test indicate?
If growth is apparent, bromthymol blue will change from green to blue to make it more apparent. However, the growth will only take place if the bacteria are able to use sodium citrate as their sole source of carbon.
How would you determine if a slant is H2S?
It would have black indicating the presence of hydogen sulfide (iron).
How would you determine if a slant is indole positive or negative?
Add Kovac's reagent, 4-5 drops. If it turns red it is positive.
How would you determine bacterial motility in a slant?
When a bacteria culture is stabbed straight down and then incubated, motile bacteria will move from the stab line and grow throughout the medium making it turbid. Nonmotile bacteria will only grow in the stab line.
How will you determine PDA in a slant?
This refers to deaminases that remove the amine group. By adding ferric chloride (several drops) you can determine whether it is positive or negative. If positive it will turn green.
What is the significance of detecting E. coli in drinking water?
This means that the water has been contaminated either directly or indirectly with fecal material, human or animal. This raises the potential threat of disease.
List five characteristics of coliform bacteria.
Gram negative. Only present in intestines of warm-blooded animals. Non-spore forming. Faculative bacilli. Ferment lactose to acid and gas within 24-48 hours.
Describe the appearance of coliforms on M-endo broth.
Pink to dark red with a golden/metallic sheen.
Is the water that passed through the filter sterile?
Yes. The membrane material of the filter is so structured by material and size of pores that all bacteria is captured and does not drain through.
Explain why the standard for municipal drinking water is different from the standard for private drinking water.
The EPA (U.S. Environmental Protection Agency) has laws that must be abided by in regard to municipal drinking water which serves a greater number of people and is the government's responsibility to see is safe. Private drinking water is the responsibility of the few people who are utilizing that supply.
How is the degree of contamination of drinking water determined to be safe?
Drinking water for private use must have less than 5 coliforms per 100 ml. Drinking water for municipal use must have no more than 1 coliform per 100 ml. Water used for recreation may have up to 1000 coliforms per ml.
Explain the procedure of inoculating a petri dish to determine coliforms in water.
Dip forceps in 70% alcohol and flame. Plase filter on holder and screw on top. Measure 10 ml of your water sample and pour over the filter. Attach filter to vacuum and turn in. After water passes through filter, use sterilized forceps and put filter on the medium in the petri dish. label and incubate.
Explain the procedure of determining coliform colonies on the incubated petri dish.
Observe and count the no. of coliform colonies (pink to dark red and will have green/golden metallic sheen). There should be between 30-300 colonies if heavily contaminated and no more than 300. Multiply the no. of colonies by 10 in order to get the no. of bacteria per 100 m..
How is the clinical diagnosis of a UTI established?
The urine is cultured in an enriched medium so that both the type of bacteria and the no. of colonies can be determined. A small amount of urine (made accurate by use of a calibrated loop) is streaked on the plate so that the entire surface is covered. This is incubated. Once incubated, the colonies are counted and this number is multiplied by the dilution factor determined by the size of the calibrated loop. A colony count of less than 10,000 per ml is an indication of normal contamination where as greater is a sign of infection. The physician will consider other factors such as the type of bacteria and other lab findings to make the final diagnosis.
Explain the accuracy of a sample from a non-midstream catch.
This sort of sample won't be accurate because it will contain both the normal flora of the urethra as well as bacteria on the mucous membranes of the genitalia.
Explain the accuracy of a sample taken 18 hours later.
This sample might be accurate, or it might not. It depends on whether or not the sample was refrigerated within two hours of being taken. It also depends on how the sample was obtained. For example if it was the result of a catheterization or a clean catch, midstream method it is probably going to be accurate whereas if it were from a non-midstream it would not.
The physician suspects her patient to have a UTI. She requests a voided urine specimen to be cultured rather than a catheterized sample. Explain her decision.
Catheterization is not a routine procedure. There is a good chance of introducing a UTI as a result of it, or of aggravating a UTI already in place. Moreover, the voided urine specimen if clean catch and midstream will give an accurate picture of the bacteria actually in the urethra.
Explain the clean catch midstream technique.
The area around the urethral meatus is cleaned with an antiseptic solution and dried with a sterile towel. The first third of urine flow will contain a high no. of bacteria from the urethra and is not collected. The second third is collected in a sterile container. The last third is exiting under less pressure and more likely to pick up bacteria from the skin and mucous membrane and so is not collected.
What biochemical test can be performed to distinguish members of the genus Staphylococcus from members of the genus Streptococcus?
Catalase is an enzyme that bacteria uses to cause hydrogen peroxide to reduce to oxygen and water. The catalase test is the main test used. This is because Staphylococcus is catalase positive and Streptococcus is catalase negative.
Why is MSA used for culturing nasal swab specimens?
One fourth of the population has Staphylococcus aureas in the nares. MSA (mannitol salt agar) contains manitol, a 7.5% salt concentration, and the pH indicator of phenol red. The salt will inhibit most bacteria besides Staphylococci. The staphylococci which are left will then ferment the carbohydrate and change the medium around the colony from red to yellow. Mannitol agar is selective and differential.
Describe the typical members of the upper respiratory tract.
A large number of bacterial species colonize the upper respiratory tract (nasopharynx). The nares (nostrils) are always heavily colonized, predominantly with Staphylococcus epidermidis and corynebacteria, and often (in about 20% of the general population) with Staphylococcus aureus, this being the main carrier site of this important pathogen. The healthy sinuses, in contrast are sterile. The pharynx (throat) is normally colonized by streptococci and various Gram-negative cocci. Sometimes pathogens such as Streptococcus pneumoniae, Streptococcus pyogenes, Haemophilus influenzae and Neisseria meningitidis colonize the pharynx. http://textbookofbacteriology.net/normalflora_3.html
Describe the appearance of gamma hemolytic organisms on SBA.
If there is no breakdown of blood on the SBA (sheep blood agar) then the bacteria is gamma hemolytic. A complete breakdown and a clearing of the medium around the colony is beta hemolytic. A partial breakdown (and formation of green color) is alpha hemolytic.
Why isn't the size of the zone of inhibition measured for the bacitracin or optochin sensitivity tests?
According to the lab atlas, the zone of clearing IS important, as anything 10mm in diameter or more around the disk means it has bactracin susceptibility. The lab atlas also says that a zone of 14mm in a 6mm disk or a zone of 16 in a 10mm disk is indicative of Streptococcus pneumoniae whereas smaller zones indicate further testing is necessary.
Name three characteristics of Staphylococcus aureus.
It is beta hemolytic. It ferments mannitol. It produces coagulase.
What hemolytic are most normal streptococci?
alpha or gamma hemolytic.
Describe the test for Hemolysis.
Bacteria is divided into one of three categories when grown on a medium that contains 5% sheep blood. There will beta hemolytics causing a complete breakdown of all the medium around the colony. There will be alpha hemolytics that cause a partial breakdown of cells and forms a green color. If there is no breakdown of the blood the bacteria will be called gamma.
Describe the test for mannitol fermentation.
This fermentation is detected by bacteria grown on mannitol salt agar. First, the salt will inhibit most bacteria except for staphylococci. The staphylococci that CAN ferment the carbohydrate changes the medium around the colony from red to yellow. (Staphylococcus aureus could do this).
Describe the test for coagulase.
This is to detect the presence of the enzyme coagulase. The bacteria has to demonstrate ability to cause the coagulation of plasma. Rabbit plasma is innoculated with the bacteria and incubated. If the bacteria is coagulase positive the liquid plasma will have turned into a solid clotted mas. You can also put a drop of plasma on a glass slide and mix in a loopful of bacteria to see if there is immediate clumping of plasma.
Describe the bactracin disk test.
This test is for the identification of Streptococcus pyogenes. A beta hemolytic streptococcus colony is streaked on a sheep blood agar plate. A bactracin disk is put in the center. It is incubated. If there is a presence of a zone of inhibition around the disk it is positive.
Describe the CAMP test.
This is named after the scientists that developed it. It is based upon the idea that there is a synergistic effect between hemolysins produced by Streptococcus aureus and Streptococcus agalactiae. A vertical streak is made down the center using S. aureus. Then another is streaked at a right angle to the first 3-4 mm from the first streak. It is incubated. Then it is positive if there is an arrowhead shaped zone of beta hemolysis at the junction of the streaks. This is ONLY seen with S. agalactiaae.
What are capnophilic organisms.
Many of the bacteria of the throat are these. They require an increases level of atmosphere CO2.
This is QUANTITATIVE. It is the degree of pathology produced by an organism to cause disease.
This is QUALITATIVE. It is the ability of an organism to cause disease
This is a pathogen but is not easily transmitted. Containment is easily accomplished.
This virus both virulent and a pathogen. It is not easily contained and there is not an effective treatment.
Main responsibilities of a hospital microbiology lab
To assist in the diagnosis of infectious disease, to clarify its presence whether caused by bacteria, viruses, fungi or parasites, and to identify effective means of control.
What is the objective closest to a slide in a microscope?
This means that you can switch from one power of a microscope to another without major refocusing.
This arrangement is a packet of 8-64.
What are three ways to control the amount of light reaching the ocular lens of a microscope?
a) the condenser: cone shaped glass that concentrates the light into a smaller space. b) the iris or aperature diaphagm. c) the diaphragm lever.
What is the proper manner of carrying a microscope?
With two hands, in front of and close to the body.
What are two ways to enhance the resolving power of a microscope?
Switching objectives and oil/immersion oil.
How does immersion oil increase resolution?
By decreasing the distortion of light. It bends light at the same angle as glass. When the light passes from the slide, through the oil, into the lens, very little refraction occurs which decreases distortion and increases resolution.
What is empty magnification?
A blurry large image.
What is the standard unit of measurement in microscopy?
What are the three components of microscopy?
Magnification, resolution, contrast.
What is meant by magnification as a component of microscopy?
The ability to enlarge an image.
What is meant by resolution as a component of microscopy?
The ability to distinguish between two distinct points (ability to reveal detail).
What is meant by contrast as a component of microscopy?
The ability to manipulate light or stain.
Name the color and magnification of the microscope objectives.
4x, scanning, red.
10x, low power, yellow.
40x, high power, red.
100x, oil immersion, white.
How does one arrive at the total magnification?
Multiply the eyepiece magnification (10) times the objective magnification.
What objective has a magnification of 1000?
The oil immersion objective.
Made impure with undesirable material or organisms.
Colony forming unit
Macroscopic cluster of cells on solid medium arising from a single cell / capable of forming a colony.
Colony derived from a single cell by asexual reproduction and sharing identical characteristics.
Organismic structure of the colony. Color, colony, form, elevation, surface luster, way it grows at the margin.
Bacteria growing closely together.
Completely free of all life forms
Three advantages agar has over other solidifying agents.
a) can be poured into plates, tubes or slanted to give more surface area. b) Few bacteria can digest. c) solid at 37C (body temperature and temperature at which most medically important bacterial cultures are grown. d) single bacterial cells will form isolated colonies on agar.
For what purpose would you use a solid medium?
This can be used to grow discrete colonies of bacteria and therefore useful in obtaining pure cultures. You can isolate different species of bacteria into pure cultures.
What is the purpose of performing a subculture?
To isolate a second generation culture from the well established colony. To "replenish" the culture.
How could you determine whether the turbidity in a broth culture was from different microbes or from the grown of only one kind of microbe?
Make a smear, use a stain, examine under a microscope. Subculture.
What is a pure culture?
Isolated and holding one identified, differentiated species of microorganism.
What is a mixed culture?
Holds two or more identified and known species.
What is a contaminated culture?
Once pure or mixed but since has had contaminants (unwanted microbes of uncertain identity) introduced to it.
What are the basic nutrients for bacteria?
A source of energy. A source of carbon, nitrogen, sulfur, phospherus. Minerals. Vitamins and growth factors. Water.
The exact composition is known.
The precise chemical composition is unknown. This is the agar normally used.
These microorganisms need complex nutrients. They are difficult to grow.
What are three types of media?
a) liquid broth. b) solid c) semi-solid.
Describe a liquid broth media.
Fast growth, when growing a large amount of one specific type
Describe a solid media.
1-2% agar. Can be used to grow discrete colonies. This is best for pure cultures. This can separate cultures (streak or streak plate technique)
Describe a semi-solid agar.
1% agar. Allows for motility of bacteria.
What are some aeseptic techiques utilized when dealing with cultures?
Flaming innoculation loop, not allowing contact of loop with anything else, not leaving tube uncovered longer than necessary, flaming neck of tube.
What is the purpose of staining bacteria and why is it necessary.
Bacterial cells are transparent and difficult to see even when magnified. The cytoplasm has little contrast from the cell's background. Stains provide contrast between the cell and the background in order to clearly see the cell's morphology (shape, size and arrangement).
What is the chemical composition of stains?
Salts, compounds of a positively charged ion and a negatively charged ion. One ion is colored (chromophore)
Describe the need of the cationic basic dye.
This cationic is positively charged. It will react with material that is negatively charged. Bacteria are slightly negatively charged.
What is methylene blue?
A cation. It is positively charged and will react with bacteria (attraction between positive dye and negative cell).
What are positively charged stains used for?
Differential staining. Otherwise the bacteria won't stain.
Cell shape, size arrangement.
What happens to bacteria after staining with crystal violet?
Gram negative bacteria appears pinkish after a simple stain procedure using crystal violet.
Why is it necessary to heat fix your slide before doing the stain procedure?
To keep the contents from washing off.
How are diplobaccili arranged?
What does staphylo refer to?
A cluster. Combined with "coccus" it describes a spherical bacteria arranged in grape-like clusters. This is not possible with bacilli.
Why do staphlobacillus not exist?
Bacillus cells only divide across the short axis.
What kind of formations do "clusters" of bacilli form?
What are the basic dyes?
Crystal violet, safranin, carbol fuchsin, methylene blue.
What are negative stains?
Acid dyes that have negatively charged chromophores and are repelled by the bacterial surface but are attracted to the glass slide. They stain the background but leave the bacteria transparent. Examples are: nigrosin, eosin, congo red.
What are the reagents in a gram stain?
crystal violet, Gram's iodine, ethyl alcohol (95% ETG), safranin
What is the purpose of Crystal violet in the gram stain?
This is the primary stain. It provides the initial contrast and colors all cells identically.
What is the purpose of Gram's iodine?
This binds with the primary cells in the cell wall. It is the mordant.
What is the purpose of 95% ETG in the gram stain?
This is the decolorizer. It removes color from some cells but not others. Gram + remains purple.
What is the purpose of safranin in the gram stain?
This is the contrasting color to the primary color. It will color the cells taht were decolorized. Gram - turns red or pinkish.
In the case of G- bacteria, what step could be omitted?
The counterstain could be omitted. We differentiated in decolorizing because G- became transparent.
In regard to gram stains, what if the bacteria lacked cell walls.
There would still be some reaction. These would retian less stain but the stain would be more easily removed.
Why is it important to limit the quantity of cells used to prepare the smear?
If these are too thick, there will not be good visualization. There will be overlapping and it will be difficult to read.
What are two factors not related to technique that could affect the outcome of Gram staining?
The age of the culture and some bacteria are uncertain in taking gram stain.
What differences are there in G+ cells that account for differential staining properties?
G+ have a thick layer of peptidoglycan in the cell wall that is composed of a network of polysaccharide attached to peptide molecules w/4-5 amino acids. Crystal violet forms large crystals in layer that are not easily removed.
What differences are there in G- cells that account for differential staining properties?
G- cells have much thinner layer of peptidoglycan surrounded by lipopolysaccharide and protein. Decolorizer dissolves these lipids, allows crystal violet and iodine to escape. Thin walls retained less stained and it was removed more easily.
What color is mycobacterium after acid-fast stain?
Red. it is acid-fast.
What color was staphylococci after acid-fast stain.
Why do acid fast and non-acid fast bacteria stain differently?
Acid fast bacteria have mycolic acid in their cell walls. They are impermeable to basic dyes unless those are combined with phenol. Once stained, acid-fast and difficult to de-stain. Gram resistant.
What is non-acid fast bacteria?
The cells that DO decolorize and are restained with the counterstain methylene blue.
What is the mordant for Kinyon AF method?
There is none except heat.
What is the arrangement of mycobacterium cells and why?
Bacillus, rope or cord-like. The lipid nature of the cell walls has a cord factor.
Name the endospore genera of medical significance with an example of species and disease associated.
Clostridium (genera), clostridium (species), tetanus (disease).
Bacillus (genera), clostridium botulinum (species), botulinum
Bacillus (genera) anthracis (species) anthrax (disease)
What is the function of an endospore?
Survival: the bacteria forms a protective structure in cytoplasm that is resistant to harsh conditions.
Describe endospores in bacillus subtilis.
Colorless. Bacillus shaped endospores. Green after endospore stain.
What is the function of a capsule?
It interferes with phagocytosis by white blood cells in the body of the host. It helps the bacteria adhere to surfaces such as host tissues.
What is the role of mycolic acids in the virulence of an organism?
Mycolic acid is within the cell walls and allow cells to be very resistant to chemicals and drugs.
What is the role of endospores in the virulence of an organism?
Endospores are formed within the cell cytoplasm to make cells very resistant to high temperatures, desiccation, toxic chemicals, radiation, changes in pH, lack of carbon and nitrogen.
What is the role of capsules in the virulence of an organism.
Capsules are extracellular layers composed of polysaccharide, a polypeptide or both. This interferes with phagocytosis by WBC's and helps the bacteria adhere to surfaces such as host tissue, resisting the body's attempts to flush away. Also involved in formation of biofilms.
What is the purpose of a negative stain?
Bacteria can be seen without being directly stained. Only the slide is stained. This allows determination of shape, arrangement and size without distinction. Also there is no heat fixation. This is very useful when bacteria are heat sensitive.
In a negative stain, why does the bacteria remain unstained and the background take the stain?
The stain is negatively charged and so are the cell walls. Therefore only the glass can attract the stain.
What are the ways to detect bacterial motility?
Hanging drop, flagellar stain, semi solid deep innoculation.
Describe motion for E. coli
Has flagellum and moves. Appears to be "swimming" multidirectional.
How can we detect brownian motion?
It is more vibratory, more random and in no specific direction.
How can we detect cellular motion?
It is flagellor, more purposeful, in specific directions, zig zag or darting.
Does Sarcina lutea have motion?
What are the reasons a motility test would be performed in a clinical lab?
To detect motility, to see bacteria in normal state, to see if flagellated or not.
Why is motility important?
For survival, when bacteria require either moving from dangerous conditions or toward nutrients. For attachment and colonization in vital organs.
Why is it important to obtain isolation of bacteria into pure culture?
Most samples are mixed with normal flora or other contamination. It is necessary to separate individual bacteria into isolated colonies.
When observing the results of a streak plate innoculation from a mixed culture, will you be able to determine how many species of bacteria were in the original sample? Explain.
Yes. After incubation of a properly streaked plate, single isolated cells reproduce forming colonies (clones or genetrically identical cells. When each CFU represents the progeny of a single bacterium, it is a pure culture.
Describe three ways to isolate bacteria into a pure culture.
1) dilution to extinction. 2) pour plate method. 3) streak plate (streaking)
What are the components of colony morphology?
Form, elevation, margin, surface, opacity, chromogenesis, consistency, emulsificity, odor.
Why should the petri dish always be upside down?
To minimize contamination, to avoid getting moisture on the agar surface; for writing and reading label.
What are some "form" descriptions?
Circular, irregular, filamentous, rhizoid.
What are some "elevation" descriptions?
Raised, convex, flat, umbonate, crateriform
What are some "margin" descriptions?
Entire, undulate, filaform, curled, lobate
What rules are there for using a petri dish?
It should be upside down. label with name, date and culture. Limit the time with the lid off. Never separate the lid from the bottom of the dish.
What are some methods by which bacterial numbers can be maintained, decreased or eliminated?
Heat, refrigeration, chemicals, radiation.
What does bactricidal mean?
What does bacteriostatic mean?
Maintains at original level.
What are disinfectants used for?
Intended for use on inanimate objects.
What are antiseptics used for?
Safe for use on human tissue.
What factors influence the effectiveness of disinfectants and antiseptics?
The concentration of chemical appropriate chemal agent and proper dilutions prepared. The length of exposure to the contaminants. The temperature. The kinds of microorganisms. The number of microorganisms and the nature of the material bearing the microorganisms.
What kinds of microorganisms are th emost difficult to control with disinfectants or antiseptics?
Bacillus, clostridium, mycobacterium, tuberculosis.
Why does UV radiation at a wavelength of 254 nm work?
It is absorbed by the DNA. This causes abnormal bonds to form between adjacent nitrogen bases on the same DNA strand. This disrupts normal DNA replication and if not repaired or if numerous the cell dies. If it survives it can be mutated.
Microorganisms present a range of resistances to chemical disinfectants and no single disinfectant is effective in all situations. Identify at least four points that should be considered when selecting a disinfectant.
1) Concentration of the chemical agent must be appropriate and properly diluted. 2) There should be the necessary length of exposure. 3) The temperature. 4) the no. of microorganisms present.
Which is more resistant to disinfectants? Gram negative or gram positive?
Gram negative has a thick outer membrane that acts as a barrier.
What are two important considerations and/or limitations when using UV radiation?
Can cause damage to skin and eyes, can penetrate glass and plastic, has the ability to mutate cells in ways that could be passed on to future generations.
What are two ways to increase antimicrobial effectiveness of UV radiation?
Longer exposure and direct exposure (remove the obstacle/lid).
Compare and contrast disinfectant and antiseptic.
Disinfectants can be used only on inanimate objects. Antiseptics can be used on both skin and human tissue. Some chemical disinfectants/antiseptics have bactericidal effect while others have a bacteriostatic.
What are the three major roles the microbiologist plays in treatment and diagnosis of disease?
1) isolate cause of infection. 2) identify the isolated organism. 3) provide physician with information in regard to treatment (antibiotic susceptibility testing).
What are two techniques for antibiotic susceptability testing?
a) agar disk diffusion. b) tube dilution method. c) e test.
Discuss differences between terms: chemotherapeutic, antimicrobial, antibiotic.
Chemotherapeutic: treatment of disease using chemical agents or drugs that are selectively toxic to the causative agent/disease. Antimicrobial: substance that kills or inhibits growth of microorganisms. Antibiotic chemical substance from one microogranism that can kill/inhibit another microbe.
Define spectrum of activity.
The range of different microbes against which an antimicrobial agent acts.
Drugs naturally produced by bacteria, fungi, etc. that are chemically modified in the lab.
Define mode of action.
Mechanism of action: antimicrobial agent's adverse reaction on cells.
How would the lab select which antimicrobials to test against the isolated pathogen?
Bacteria that has been isolated would be grown in the presence of several chemotherapeutic agents in an effort to determine which would be the most effective in control or elimination.
Would the drug in this case have a broad or narrow spectrum? Drug A interferes with the peptidoglycan synthesis.
Broad spectrum drug breaking down portions of the cell wall as they grow/divide. They inhibit the peptidoglycan from forming peptidoglycon cross links.
Would the drug in this case have a broad or narrow spectrum? Drug B interferes with 70S ribosome function.
Narrow spectrum drug that inhibits protein synthesis which takes place in a ribosome.
Would the drug in this case have a broad or narrow spectrum? Drug C interferes with the synthesis of a vitamin.
Broad spectrum drug. These drugs interfere with absorption of numerous vitamins with many benefits.
Enriched, differential or selective medium? Agar containing 8.5% CaC12 to increase osmolarity of a medium.
Enriched, differential or selective medium? Agar containing factors which inhibit gram-positive bacteria growth, such as bile salts and crystal violet.
Enriched, diferential or selective medium? Agar which turns blue when galactose is fermented.
What is the purpose of eosin and methylene blue dyes in EMB agar medium?
PH indicators, making it possible to distinguish lactose fermenters from lactose non-fermenters.
What is the purpose of blood in blood agar medium?
Used to grow fastidious organisms requiring a rich media providing many nutrient/growth factors that are largely supplied by blood.
What is the purpose of lactose in EMB agar medium?
Bacteria fermenting lactose produce acids which lead to the formation of a dark colored colony. Those not fermenting the carbohydrate produce a lighter colored colony.
Compare and contrast differential and selective media.
Differential: helps distinguish closely related groups of bacteria. The media can grow different types of bacteria, taking on different characteristics to make them distinguishable. Selective will inhibit the growth of some bacteria while allowing others to grow. This is useful in inhabiting normal flora in order to detect pathogenic bacteria. Some media (EMB/PSA) possess both qualities.
How might selective media be used in a clinical laboratory?
Identification of whether a patient has a UTI.
What steps are necessary to identify an etiologic agent causing infection?
1) Isolate using selective medium (MSA-G+) (EMB-G-) 2) Isolate: differential medium- Cologase (G+) lactose fermentation nitrate production. 3) Confirm gram morphology.
Explain why the formation of a red color after addition of Zn powder to the nitrate test is a negative result.
If nitrates are still present the zinc will reduce them to nitrates, which will then react with the reagents already in the tube causing the medium to turn red. This means that the bacteria did not reduce the nitrates and is interpreted as a negative reaction.
SIM medium contains ferrous iron ammonium sulfate. Explain its purpose.
It is used for performing the hydrogen sulfide indole and motility test.
A substance/compound that is added to a system in order to bring about a chemical reaction.
For which tests was the addition of a reagent necessary to obtain results?
E.coli: 10 drops of sulfanic acid (reagent A) and ten drops of napthylamine (reagent B). Acinebacter the same.
What results did you obtain for Pseudomonas in the phenol red carbohydrate tubes?
Alkaline. Turned red when reagents were added to the test tube.
Explain the function of the 0.1% agar in the nitrate medium for the nitrate reduction test?
What is antigen shifting? Which protozoa use this mechanism to evade host defense?
Environmental stressors trigger to activation of genes that results in the creation of the endospore
Performance of the "factor requirement test" for haemophilus involves the
Recommended textbook explanations
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Why are individual chromosomes more difficult to see during interphase than during mitosis?
The deep ocean is within the aphotic zone and is also very cold. Suggest some of the unique characteristics that might enable animals to live in the deep ocean.
Test your vocabulary by matching each term to its definition, as identified by its preceding letter code. A. Observable characteristics in an organism. B. Allele that will only express its trait in the absence of the dominant allele. C. Phenotypic characteristic (e.g. red hair). D. Possessing two different alleles of a particular gene, one inherited from each parent. E. Sequences of DNA occupying the same gene locus (position) on different, but homologous, chromosomes. F. The process of double nuclear division (reduction division) to produce four nuclei, each containing half the original number of chromosomes (haploid). G. A change to the DNA sequence of an organism. This may be a deletion, insertion, duplication, inversion or translocation of DNA in a gene or chromosome. H. The exchange of alleles between homologous chromosomes as a result of crossing over. I. Allele that expresses its trait irrespective of the other allele. J. Chromosome pairs, one paternal and one maternal, of the same length, centromere position, and staining pattern with genes for the same characteristics at corresponding loci. K. The allele combination of an organism. a. alleles b. dominant c. genotype d. heterozygous e. homologous chromosomes f. meiosis g. mutation h. phenotype i. recessive j. recombination k. trait
Adult stem cells in the brain can produce A. nerve cells. B. muscle cells. C. skin cells. D. egg cells.