Microbiology Lab Practice Exam

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• During a sterility check, what would indicate contamination?
• What is a colony forming unit (CFU) in this context?
• In disk diffusion testing, which statement is true?
• What is the acceptable range of CFU per plate to consider a plate viable?
• How would the pH of the stain affect staining when using basic vs acidic stains?
• Rank the following antibiotics for Staphylococcus epidermidis infection from most to least effective according to the described results: novobiocin, gentamicin, penicillin.
• Which statement best describes oxygen's role in microbial growth?
• What is the purpose of inverting poured plates during incubation?
• Osmolarity refers to the concentration of solutes within a solution.
• Why are sterility controls important when preparing media and reagents?
• What is an API strip and how is it used in bacterial identification?
• According to the experimental results, which antibiotic was less effective against Staphylococcus epidermidis?
• Why are endospore-forming bacteria more difficult to eradicate and what biosafety implication does this have?
• In a disk diffusion experiment, what constitutes a proper set of controls?
• Most microbes thrive in which pH range?
• Define MIC and describe how it differs from the zone-of-inhibition measurement.
• What is the expected Gram reaction and morphology for Staphylococcus aureus on a Gram stain?
• In fermentation tests, what does gas production indicate?
• Viable plate counts are accurate at which concentration ranges?
• In VP test interpretation, what does a positive result indicate about acetoin production?
• Why are the caps loosened on a tube of agar when heating it?
• How do the different oxygen requirements (aerobic, anaerobic, facultative) influence incubation conditions?
• How does alcohol fix bacteria?
• Which counterstain in Gram staining colors Gram-negative cells pink?
• What constitutes an isolated colony in a plating experiment?
• Provide the typical temperature ranges for mesophiles, psychrophiles, and thermophiles.
• Escherichia coli infection is commonly associated with which exposure?
• What characteristics would you expect when using Sabouraud dextrose agar for fungal isolation?
• How is the oxidase test used in bacterial identification and what result is typical for Enterobacterales?
• Resident flora are defined as what?
• What is the correct order of the five classic steps in the quadrant streak technique?
• Can iodine be added before the primary stain in a Gram stain?
• Influenza viruses are divided into which major groups?
• Where should sharps be disposed of in the laboratory?
• Are normal flora considered part of the body's innate defense?
• What is the primary purpose of plating in a viable plate count?
• Which statement best differentiates halotolerant microbes from halophiles?
• After vaccination, how long does it typically take for influenza antibodies to develop?
• What factors influence the accuracy of colony counting on a plate, and how can you improve accuracy?
• Which practices help prevent PCR contamination during DNA amplification?
• Why might a physician perform a Gram stain before prescribing an antibiotic?
• Why might Gram-positive bacteria more than 24 hours old stain Gram-negative?
• Antimicrobial agents are defined as which of the following?
• In negative staining, which of the following is a typical step?
• Why is labeling and documentation important in microbiology experiments?
• Which practice best supports aseptic technique during transfers?
• Which genus is commonly associated with rapid urease activity in urease tests?
• How are transient flora acquired?
• In the Schaeffer-Fulton endospore staining method, which statement correctly describes the staining outcome?
• Which statement about influenza is true?
• If you performed a Gram stain on human cells, what would happen?
• In calculating CFU/mL, what does the dilution factor depend on?
• How do streak plating and pour plating differ in technique and purpose?
• What is the primary reason Gram staining is not used alone to identify bacteria?
• How would you recognize a mixed culture on a streak plate and what steps would you take to obtain pure isolates?
• What is the difference between a live/dead stain and a standard Gram stain, and when would you use each?
• After the Gram stain procedure, what color do Gram-negative cells appear due to the counterstain?
• Which statement correctly describes MacConkey agar as a selective and/or differential medium?
• What is one benefit of normal flora?
• Which lens type allows light to enter more easily?
• True or false: Getting a flu vaccine guarantees 100 percent protection against influenza.
• What does the zone of inhibition indicate in susceptibility testing?
• How is turbidity measured to estimate microbial growth, and what is a common limitation?
• Why is iodine used in Gram staining?
• What does a positive acid-fast stain indicate and which genera are typically acid-fast?
• During sterile transfers between containers, which step helps maintain sterility when opening a lid or cap?
• What is the purpose of including negative controls in PCR experiments?
• What is the primary value of a simple stain?
• What factors can cause some Gram-positive cocci to appear Gram-negative or inconsistent, and how should you interpret such results?
• Direct staining is characterized by which statement?
• Indirect contact transmission occurs by?
• Gentamicin primarily targets which type of bacteria?
• If Gram-positive cocci appear Gram-negative or inconsistently, what is a recommended corrective step?
• Adding distilled water to the slide before staining serves to:
• What is the typical duration for the active culture step in this context?
• An infectious disease is caused by
• What happens if too much heat is applied during heat fixing?
• A 1:10^4 dilution is prepared and 0.1 mL is plated. 26 colonies grow. Calculate CFU/mL in the original culture.
• Can dyes other than methylene blue be used for direct staining? Briefly explain.
• What are the key components of autoclave validation and how do process and biological indicators differ?
• Novobiocin is produced by which genus?
• Which factors influence the type and number of normal flora in a region?
• Compare streak plating and spread plating in terms of what they reveal about the culture and the typical outcome.
• Which statement correctly describes the MR and VP tests and what a mixed interpretation might indicate about a bacterium?
• What property allows Gram-positive cells to retain crystal violet-iodine complex after the decolorization step?
• Which combination of items correctly lists components of a standard light microscope?
• What structural feature allows Gram-positive cells to retain the crystal violet-iodine complex?
• Enzymes that drive microbial metabolism typically function within:
• Transient flora are defined as what?
• Binary fission is ...
• Penicillin's primary mechanism is to inhibit what aspect of bacterial cell biology?
• Normal flora can cause disease under which conditions?
• Based on the calendar, is it necessary to perform more than one experiment at a time to meet all due dates?
• Which statement about influenza vaccines is true?
• In a disk diffusion assay, what does a larger zone of inhibition around an antibiotic disk indicate?
• What is the principle of the catalase test and how does it distinguish Staphylococcus from Streptococcus?
• What types of control strains are essential in antibiotic susceptibility testing and why?
• Negative staining is useful for what purpose?
• Transient flora on the skin are best described as:
• In gel electrophoresis, what characteristic of DNA fragments determines their migration rate?
• What is the purpose of a negative stain, and in what situations would you use it?
• List the steps of the Kirby-Bauer disk diffusion method for antibiotic susceptibility testing.
• In MR and VP tests, if both results are negative, what does that suggest about the organism's glucose metabolism?
• What is the basic principle of gel electrophoresis in DNA analysis?
• Which factors influence where microbes are found in the environment?
• Which item is NOT typically considered essential PPE in BSL-2 labs?
• How many types of influenza viruses are included in vaccines each year?
• In acidic staining, what is the typical appearance described?
• Which purpose describes heat-fixing a smear?
• Why was Koch's recommendation for fixing and staining important for microbiology?
• What is the total magnification when using the high dry objective lens (40x) with a 10x ocular?
• What is the primary purpose of capsule staining and how are capsules typically visualized?
• The material notes that collecting a sample from around the gums for staining raises what biosafety concern?
• How would you verify that your culture medium has not been contaminated prior to use?
• Normal flora are bacteria that typically inhabit which parts of the human body and help defend against invading pathogens?
• Clostridium botulinum is primarily associated with which scenario?
• What is the primary purpose of a Gram stain and which reagents are traditionally used?
• Why are plate counts of 30-300 considered viable?
• Define CFU/mL and provide the general formula used to calculate it from a plating experiment.
• Provide a brief overview of what carbohydrate fermentation tests measure and how results are interpreted.
• Which statement is correct about basic stains for direct staining?
• How is the zone of inhibition interpreted to categorize an isolate as susceptible, intermediate, or resistant?
• What are the four phases of the microbial growth curve and their defining features?
• After Gram staining, what color do Gram-positive cells typically appear?
• Direct contact transmission occurs by which means?
• If you performed a Gram stain on a sample from pure culture of bacteria and observed a field of red and purple cocci, adjacent cells were not always the same color. What do you conclude?
• Salmonella infection is most commonly associated with which exposure?
• Approximately how many total hours should you allocate to complete a lesson that includes active culture, pouring plates, and incubating microbes?
• Penicillin is produced by which mold?
• Penicillin is described as bactericidal because it does what?
• Listeria monocytogenes infection is commonly associated with which exposure?
• How many microns are in 20 millimeters?
• Describe how you would design a small experiment to compare two antibiotics using a disk diffusion assay, including controls and replication.
• Which of the following bacteria is commonly part of normal skin flora?
• Which organism produces gentamicin?
• How do you perform a motility test in semisolid agar, and what indicates motility?
• In antibiotic susceptibility testing, why is preparing a standardized inoculum important?
• What is the main characteristic of negative staining compared with direct staining?
• In Schaeffer-Fulton staining, what color do vegetative cells appear after the safranin counterstain?
• How should microbiology waste be disposed of after use?
• Which statement best defines bactericidal antibiotics?
• Which statement accurately describes selective and differential media with an example for each?
• In the example given, which organism's colonies are used to illustrate colony forming units?
• Which step can be omitted without affecting determination of Gram reaction?
• Which statement correctly contrasts antibiotics with antimicrobial agents?
• What does the indole test assess and what does a positive result indicate?
• Which of the following is NOT a standard part of a light microscope?
• Penicillin is best described as which spectrum?
• Could any dye be used in place of nigrosine for negative staining?
• What is the citrate utilization test used to determine and what indicates a positive result?
• When counting colonies, why would you perform multiple plates and replicate measurements?
• Which type of influenza vaccine is delivered via intranasal spray?
• Pathogens are best described as
• Why is the size more accurate in a negative stain than in a direct stain?
• A contagious disease is defined as a disease that
• What is the role of heat fixing in the Gram stain, and what can excessive heat cause?
• What is a primary function of vaccines?
• If you allowed your dilution tubes to incubate for 24 hours before plating them, do you think the results of the experiment would be impacted? Assume that unlimited resources are present in the tubes.
• What is the correct sequence of reagents used in a standard Gram stain?
• If Gram stain shows a mix of Gram-negative rods and Gram-positive cocci in the same field, what could be true?
• Why is proper labeling of culture plates essential in a microbiology lab?
• In viable plate counting, what is assumed about colonies on a plate?
• In a capsule visualization using India ink (negative staining), how does the capsule appear?
• Indirect transmission of pathogens can occur through which routes?
• What does CFU stand for?
• Which statement best describes the subdivision of influenza viruses into subtypes and strains?
• Suppose you observe red rods and purple cocci in the Gram-stained field. What do you conclude?
• Which statement best describes the growth of facultative anaerobes?
• Which practice is characteristic of BSL-2 microbiology laboratory work?
• Which delivery method is used for the live attenuated influenza vaccine?
• To remove transient flora from the skin, the most effective practice is:
• Novobiocin's mechanism targets which enzyme?
• What is the purpose of aseptic technique during plating?
• Which set of items constitutes essential PPE for typical BSL-2 work?
• What best defines normal flora?
• What is the purpose of using oil with the oil immersion objective lens?
• Isotonic conditions are those in which the solution inside and outside the cell are:
• Which describes a hypotonic environment for a microorganism with a cell wall?
• What are common Gram stain troubleshooting issues and how would you address them?
• What is the primary purpose of aseptic technique in a microbiology laboratory?
• Which pair of genera are among the major sources of antibiotics used clinically?
• What is the standard sterilization method and parameters that effectively destroy endospores?
• Which chemical can be used as an alternative fixative to heat fixing?
• In carbohydrate fermentation tests, what does a color change from red to yellow typically indicate?
• Describe the urease test principle and interpret a rapid strong pink color within 24 hours.
• In a hypertonic solution, water moves out of the cell and the cell shrinks.
• Normal flora defend the host by what mechanism?
• Parfocal means what?
• Which environmental factors influence microbial growth in an environment?
• Which factor is NOT listed as influencing microbial growth in the environment?
• Which organism is commonly considered part of normal human skin flora?
• In the Gram stain, which sequence correctly lists the major steps?
• In an average year, approximately what percent of Americans contract influenza?
• Normal flora are found in which body areas?
• Which organisms are particularly observed with negative staining due to their characteristics?