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104 Cards in this Set
- Front
- Back
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Describe the function of the following ingredients found in the culture media: Nutrient Broth, Beef extract
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Food/Protein
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Describe the function of the following ingredients found in the culture media: Nutrient Agar, Agar
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Solidifying agent
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Describe the function of the following ingredients found in the culture media: Phenol Red Broth, Phenol red
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Acid/base indicator
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Describe the function of the following ingredients found in the culture media: Eosin Methylene Blue Agar, Methylene blue
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Inhibiting dye
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Describe the function of the following ingredients found in the culture media: Anaerobic Agar, Methylene blue
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Oxidation/Reduction indicator
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Describe the function of the following ingredients found in the culture media: Azide Blood Agar Base, Sodium azide
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Inhibiting agent
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Describe the function of the following ingredients found in the culture media: Thioglycollate Medium, Sodium thioglycollate
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Reducing agent
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Describe the function of the following ingredients found in the culture media: Mannitol Salt Agar, Sodium chloride
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Inhibiting agent
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Describe the function of the following ingredients found in the culture media: Brilliant Green Agar, Lactose
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Food/Sugar
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What % agar is used in the nutrient (or tryptic soy) agar medium?
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1.5%
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Why should agar be boiled before sterilization?
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To insure that it completely dissolves.
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Why should agar be cooled to 45oC before pouring?
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To reduce condensation and to provide easier handling of liquid medium.
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At what temperature does agar solidify? Melt?
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42oC ; 100oC
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Why is agar not used as a food by most bacteria?
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It is composed of cellulose and is not digested by most bacteria.
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What are the advantages of agar over gelatin as a solidifying agent.
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Gelatin contains protein and can be digested by most bacteria which would transform the gel into a liquid medium. Agar is seaweed made of cellulose which bacteria cannot digest.
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State the value of: differential media
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produces color changes in response to differences in reactions by bacteria such as differences in fermentation of sugars; contains fermentable sugars or other differential agents.
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State the value of: selective media
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inhibits the growth of certain organisms while allowing others to grow; contains inhibitory dyes or chemicals.
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State the value of: enrichment media
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enhances the growth of certain desired organisms; contains special additives or nutrients to enhance growth.
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State the value of: transport media
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allows transfer of specimen from patient to lab without affecting specimen in any way; contains chemicals that do not allow specimen to multiply or dry out.
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State the value of: all purpose media
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allows for the growth of almost any type of bacterium; contains basic food materials.
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List several simple and complex sources of carbon
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Simple: CO2 /CH4
Complex: Sugars/lipids/proteins |
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List several simple and complex sources of nitrogen
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Simple: N2 /NO2 /NO3
Complex: Amino acids |
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Why is pH an important factor in culture media preparation?
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Bacteria possess rather specific ph growth ranges. Culture media that is too acidic or too alkaline will inhibit the growth capabilities of the organisms
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Contrast chemically non-defined culture media with chemically defined media. Provide some examples of both non-defined and defined foods that would be consumed by humans.
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Chemically non-defined media contains unknown chemicals and/or unknown amounts of these chemicals. It cannot be reproduced exactly each time. Nutrient Agar media that contain beef extract would be a good example. Chemically defined media can be reproduced exactly and contains very precise types and amounts of chemicals. Fermentation media such as Phenol red Glucose broth would be a good example. Humans consume hot dogs and canned meats that are common non-defined media. Sugar and water mixed together would be an example of a chemically defined medium.
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What are the main benefits of the petri plate? Of the rodac plate?
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Petri plates provide a large, solid surface area for bacterial colony formation and are useful for isolation and purification of bacteria. Rodac plates are press plates only. They are used to check surfaces, floors, walls.
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What precautions must be taken to prevent contamination when pouring agar plates?
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Hold lid over plate when pouring; flame lip of bottle holding melted agar; recover dish when finished.
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Why must bottles of melted media be cooled to 50oC before pouring?
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To reduce condensation and to provide easier handling.
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Why should swabs remain in the sterile tube just prior to use?
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To avoid contamination.
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Why must agar plates be inverted during incubation?
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To avoid excessive condensation from lid.
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At what temperature does tryptone soy agar (or NA) solidify?
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42oC
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At what temperature does tryptone soy agar (or NA) melt?
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100oC
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Why is it necessary to hold the lid of the petri plate over the bottom during bacteriologic manipulation?
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To reduce airborne contamination.
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List the sources where you found Gram positive bacilli. Explain their presence and possible medical significance.
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Many of the Gram + bacilli produce endospores which would be found in dust, on insects, tops of tables, the floor, in the air, etc. Endospore forming bacteria are commonly found in the soil and the endospores can be carried to almost any place by the wind or on dust. Endospores are very resistant. Disease causing endospore formers include Bacillus anthracis (anthrax), Clostridium tetani (tetanus), and others.
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List the sources where you found Gram negative bacilli. Explain their presence and possible medical significance.
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All Gram - bacilli possess endotoxins which allow them to survive in the water and soil, on insects, etc. They are most commonly found in aquatic environments because they can rapidly divide and their endotoxins can inhibit the development of others. Disease causing Gram negative bacilli include E. coli (colitis), Pseudomonas aeruginosa (cellulitis and skin infections), and Shigella boydii (shigellosis).
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List the sources where you found Gram positive cocci. Explain their presence and possible medical significance.
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Gram + cocci are commonly found on the skin and mucous membranes of man and animals. The body provides a natural environment for these commensals. Disease causing Gram + cocci include Staphylococcus aureus (skin and nosocomial infections) and Streptococcus pyogenes (strep throat, scarlet fever).
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How could the number of microbes in an environment be controlled.
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Controlling the dust in the air by means of air filters and regular cleaning and greatly decrease the microbial contamination.
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Are bacteria ubiquitous? Why? Define the term.
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Yes. Bacteria are found literally everywhere and in every environment.
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Why did we use Sabourauds dextrose agar (SDA) as a culture medium to test the floor or your shoe?
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This medium is designed to promote the growth of molds and yeast. Some bacteria will grow but if molds and yeast are present on the floor or in the shoe they will slowly grow and be visible after 2 to 3 days.
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What precautions should one take to prevent lab contamination of culture media?
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Keep the culture plates covered; use aseptic technique; avoid dust and airborne contaminants; keep media in refrigerator.
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From what does a bacterial colony arise? How do bacteria accomplish this?
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Bacterial colonies arise from a colony forming unit (CFU) or a single cell. A cell or group of cells can divide rapidly by binary fission and produce many cells.
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Why is it important to note colony morphology?
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Because colony morphology is characteristic of each type of bacterium and it can then be used in its identification.
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How can bacteria produce such a variety of colony shapes, sizes, and textures?
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Because each genus may be genetically different in their method of reproduction, their waste product production which can affect their growth patterns, and how they accumulate on the plate to form into colonies.
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Why is it difficult to obtain isolated or pure colonies when you make a simple streak plate?
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Because a simple streak plate technique does not allow for the separation of individual cells or colony forming units (CFU's) to allow for the formation of isolated pure colonies. In order to produce pure colonies you must use a streak plate technique that will separate the cells sufficiently
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How can a single colony on a plate be used to start a pure culture?
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Single colonies contain millions of bacteria and can arise from a single cell. Single cells divide by transverse (binary) fission and given a few hours will form large masses of cells.
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What is meant by the term, "colony morphology"? List 6 colony characteristics.
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It is the study of the structure and characteristics of bacterial colonies that form on the surface of an agar plate. The characteristics could include: size, texture, odor, color, form, elevation, and margin.
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Why is it important not to contaminate a pure culture?
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Once a pure culture is contaminated, all its characteristics and biochemical reactions could change because it no longer contains only one kind of organism.
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How could you determine if culture media given to you is sterile before you use them?
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Incubate the plates, tubes, etc., for 24 hours prior to use and then observe for contamination.
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Comment on the practicality of agar as a solid culture medium for bacteria.
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The agar allows the bacteria to grow on the surface and form into characteristic masses called colonies. It can also be used for isolation and purification of organisms.
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State the purpose of the streak plate technique.
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It provides a method of separating individual cells by means of a sterile loop, hopefully allowing them to form into pure colonies.
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Contrast the difference between an isolated pure colony and an isolated mixed colony.
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An isolated colony may not have formed from a single cell and may still be mixed (isolated mixed colony). An isolated pure colony will contain only one kind (genus and species) of organism since it arises from a single cell or CFU.
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Why are swabs not suitable for use in isolating pure colonies?
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Swabs can not separate the individual cells enough for isolation and would only form a mass of growth.
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State what is meant by a "pure" culture. Why is it important to study only pure cultures?
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A "pure" culture is one that contains only one type (genus and species) of bacteria and one that arises from a single cell or CFU. A pure culture allows us to study its morphological and chemical features.
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Why are aseptic techniques so important in the isolation of pure colonies?
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Without aseptic techniques, contamination would occur. This would make it impossible to isolate pure colonies.
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When an agar plate is streaked for isolation, why is the loop sterilized in between each section of the plate?
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The loop is sterilized to reduce the number of bacteria being streaked on the plate. Only those bacteria originally placed on the plate can be transferred to the next section.
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List four aseptic techniques which should be performed during the streak plate procedure.
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(1) Sterilize the loop before and after use; (2) Cover the plate each time; (3) Streak the plate at an angle to avoid airborne bacteria; (4) Sterilize the lip of the culture tubes.
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Discuss the desirability and composition of agar stock slants.
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Agar stock slants contain tryptone soy agar, which is an all purpose medium and provides a large protected surface area for growth. If refrigerated, it can maintain the culture for several weeks or months. Slants are also easier to store and have less contamination than plates.
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List and describe three techniques of pure culturing.
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1. Pour plate method - requires the test specimen to be pipetted into a sterile dish; 2. Spread plate method - requires the test specimen to be spread over the surface of an agar plate by means of a bent glass rod; 3. Streak plate method - requires the test specimen to be streaked onto the surface of an agar plate by means of a sterile inoculating loop.
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Why can you find anaerobes in soil samples? Of what medical importance is this finding?
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Soil conditions are often anaerobic. Tetanus endospores and gangrene endospores can be present in soil and may infect soil contaminated wounds.
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Why can you find anaerobes in the oral cavity? Of what medical importance is this finding?
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Areas around and underneath the gums are often anaerobic. This provides conditions for decay and for the development of anaerobes which may contribute to periodontal infections.
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Why is a reduced environment necessary for anaerobes?
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A reduced environment removes oxygen and helps to maintain the anaerobic condition.
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How can you determine if a thioglycollate tube contains a properly reduced environment. Why?
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Anaerobic indicators such as resazurin can be added and will turn pink in the presence of oxygen. Methylene blue will turn blue in presence of oxygen.
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How can decaying material create an anaerobic environment?
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Decaying material removes oxygen from the environment and thus creates an anaerobic condition. Dead or dying tissue creates dead or dying tissue.
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What does a catalase test indicate about an organism?
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The test indicates whether the organism possesses the catalase enzyme which can break down H2O2 which forms during aerobic metabolism. It indicates the organism can probably grow in the presence of oxygen.
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Why should anaerobes from the soil possess endospores?
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Conditions often become unfavorable for bacterial growth because of drought, freezing, and high heat. Possessing endospores allows these organisms to survive until conditions become favorable.
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Which cultures grow under the anaerobic environment
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Clostridium, E. coli, and soil sample.
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Which cultures grow under aerobic environment
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E. coli, Sarcina, and soil sample.
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Which cultures grow under both environments (anaerobic and aerobic environment)
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E. coli, and soil sample.
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Why do organisms possess both aerobic and anaerobic systems?
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This allows these organisms to survive under a variety of environmental conditions.
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How can you tell whether an aerobe or an anaerobe is growing in thioglycollate broth?
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Aerobes tend to grow only on the surface where oxygen is present while anaerobes tend to grow only towards the bottom of the tube where oxygen is absent. A catalase test could help to identify the organism; anaerobes tend to lack the catalase enzyme.
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What is the difference between a candle jar and an anaerobe jar in creating anaerobic conditions?
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A candle jar creates a CO2 environment which will help microaerophiles to grow while an anaerobe jar creates an anaerobic environment with H2 and CO2 gases.
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T/F:
Semi-solid tryptone soy broth is used for growing bacteria in Petri dishes |
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T/F:
Pure colonies can develop from one single bacterial cell or a colony forming unit |
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T/F:
Broth tubes can be used to exhibit morphology features such as color, texture and elevation |
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T/F:
When streaking a plate using the dilution steak plate method, the loop must be flamed at least 6 times if you follow the proper procedure |
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T/F:
Anaerobes can be found in the soil and even in the oral cavity such as under the gums |
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T/F:
A differential medium enables you to tell the difference between bacteria and viruses |
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T/F:
If you don't invert your Petri dishes when they are incubated, you can get a lot of condensation to build up under the lid |
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T/F:
The best microscope to use when studying colony morphology would be a dark-field microscope |
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T/F:
After each lab used Petri dishes should be carefully discarded in the trash |
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T/F:
The Clostridia used in lab are classified as strict aerobes that form endospores |
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Peptones found in a culture medium would act as
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Protein/food
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A good selective medium used to grow molds would be
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Sabourauds Agar
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Pellicles, tubidity, and flocculent formations of bacteria can be seen in
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Broth tubes
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A pure culturing technique involving the use of a sterile bent glass rod is called
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spread plate technique
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Thioglycollage added to a culture tube would
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act to treat anaerobic conditions
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What is true concerning agar (agar-agar)
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composed of cellulose which isn't disgestible
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G+ bacilli
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include disease causing members such as tetanus and anthrax
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Which of the floowing is not usually observed on agar plates
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turbidity
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A stock slant
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can be used to preserve pure cultures for weeks or months
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T/F:
A non-defined culture medium for humans would be like a hot dog |
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T/F:
A rodac plate is normally inoculated by means of sterile swabs |
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T/F:
Solid specimens sch as hamburger should be mixed in sterile water prior to using an isolation technique |
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Anaerobes can't grow in
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candle jars
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When a methylene blue pad is placed in an anaerobe jar and turns blue, this would mean
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that the system didn't work and air is still present
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A transport medium actually doesn't contain any nutrients which would allow organisms to grow |
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Ubiquitous means
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bacteria can be found everywhere
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A pure culture is the same as an isolated mixed culture |
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T/F:
Swabs can usually be used to created isolated pure colonies |
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A faculatative anaerobe
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includes intestinal organisms such as E. coli
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Disodium phosphate found in a culture medium acts as
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buffer
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G+ cocci are commonly found on toilet seats and chairs because they are common skin commensals |
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All motile bacteria produce a red pigment |
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T/F:
A saline water blank is an osmotically balanced salt solution |
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Isolated mix colonies
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should never be used to prepare pure stock cultures
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