30 Questions
What is the purpose of the anaerobic indicator strip used in the jar?
To monitor the presence of oxygen in the jar
Which of the following organisms is able to grow in both microaerophilic and anaerobic conditions?
Staphylococcus aureus
What is the purpose of the paper sachet that is placed in the jar?
To create an oxygen-free environment inside the jar
Which of the following organisms is able to grow in aerobic conditions but not in anaerobic conditions?
Pseudomonas aeruginosa
What is the purpose of the heat and condensation observed on the walls of the jar during the incubation period?
It is a quality control check to ensure the jar is properly sealed
Which of the following organisms is able to grow in microaerophilic conditions but not in anaerobic conditions?
Campylobacter jejuni
What is the primary objective of the four-quadrant streaking method?
To quantify the number of colonies present
When interpreting colonial morphology on non-differential plates like TSA and CHOC, which of the following is the MOST important observation to make?
Gross colonial morphology
Which of the following is the BEST approach to interpreting broths during result interpretation?
Look for the presence of turbidity throughout the broth
What is the PRIMARY purpose of performing a Gram stain during the flow of work in clinical microbiology?
To distinguish between Gram-positive and Gram-negative bacteria
Which of the following is the MOST important step in the flow of work for clinical microbiology?
Obtaining a pure culture of the suspected pathogen
Which of the following is the MAIN difference between the standard four-quadrant streaking method and the streaking method used for urine cultures?
The four-quadrant method is used to obtain a pure culture, while the urine streaking method is used for quantification
What technique is used to observe true motility of an organism?
Wet mount preparation
Which step in the Gram staining procedure decolorizes gram-negative bacteria?
Decolorizer application
What is the primary purpose of using selective media in microbiology?
To inhibit the growth of unwanted microorganisms
Which media used in Lab 7 could be classified as both selective and differential?
MacConkey (MAC) Agar
What is the primary reason for overdecolorization during the Gram staining procedure?
Excessive decolorizer application
Based on the Lab 7 results, which statement is correct?
One organism was gram-positive, and the other was gram-negative
Which of the following is NOT a factor to consider when performing antimicrobial susceptibility testing (AST)?
The patient's age and gender
What is the purpose of performing antimicrobial susceptibility testing (AST) on an isolate?
Both (a) and (b)
Which of the following is NOT a standard element for antimicrobial susceptibility testing (AST)?
The incubation must be performed at room temperature for 48 hours
Which of the following statements about antimicrobial susceptibility testing (AST) is correct?
AST is not performed on bacteria known to be predictably susceptible to common antimicrobial agents
Which of the following is NOT a method for antimicrobial susceptibility testing (AST)?
Antibiotic gradient electrophoresis
What is the purpose of using a standard inoculum when performing antimicrobial susceptibility testing (AST)?
To standardize the number of organisms used in the test
What is the purpose of the purity plate in the disk diffusion test?
To ensure that the bacterial suspension used for inoculation is pure and uncontaminated.
Why is it important to maintain a distance of 24 mm between the centers of adjacent antibiotic disks on the agar plate?
To prevent the zones of inhibition from overlapping, which could interfere with accurate measurement.
What is the purpose of using a 0.5 McFarland standard suspension of bacteria for inoculating the agar plate?
To ensure a consistent and standardized inoculum density for reliable interpretation of results.
What is the purpose of incubating the inoculated agar plate overnight at 37°C in ambient air?
To mimic the body temperature and aerobic conditions encountered in human infections.
In the disk diffusion test, what does a larger zone of inhibition around an antibiotic disk indicate?
The bacterial strain is susceptible to the antibiotic.
Which step in the disk diffusion test involves comparing the measured zone sizes to established interpretive criteria?
Interpreting the results as susceptible, intermediate, or resistant.
Study Notes
Lab 3 - Slide Techniques for Motility
- Motility can be detected using wet mount, slide, and flagellar stain techniques
- Wet mount preparation involves mixing TSB with fresh organism and incubating for a few hours, then observing under a microscope at 40X without a coverslip
- True motility is characterized by movement in a given direction or tumbling
Lab 3 - Results
- Gram stain procedure involves methanol, crystal violet, iodine, decolorizer, and safranin
- Gram stain results report Gram reaction (+ or -), shape, and arrangement
- Errors to avoid include overdecolorization, underdecolorization, and smearing too thick
Lab 4-6 - Gram Stain Review
- Review of Gram stain procedure and results from Lab 3
Lab 7 - Selective and Differential Media
- Selective media: MAC, PEA
- Differential media: MAC, PEA, BAP
- Organisms present in broth: two, one Gram-positive, one Gram-negative
- Inhibited growth: Gram-positive on MAC, Gram-negative on PEA
Lab 7 - Atmospheric Conditions
- Anaerobic and microaerophilic conditions created using jars and Gas Pak systems
- Quality control: testing GasPak system's ability to support anaerobic bacterial growth
- Atmospheric conditions results:
- Staphylococcus aureus: aerobic, microaerophilic, anaerobic
- Pseudomonas aeruginosa: aerobic, microaerophilic, not anaerobic
- Campylobacter jejuni: not aerobic, microaerophilic, not anaerobic
- Clostridium perfringens: not aerobic, not microaerophilic, anaerobic
Lab Review so far (Lab 1-7)
- Review of Lab 2-7 procedures and results
Lab 2 - Review of Streaking
- Standard method: Four Quadrant Streaking
- Objective: to obtain gradient, pure colonies
- Streaking for urine is different, helps with colony counting and quantification
Lab 3 - Review of Result Interpretation
- Interpretation of colonial morphology: utilize gross colonial morphology, add details from plate
- Interpreting broths: look for turbidity, clumps, and pure culture
Antimicrobial Susceptibility Testing (AST)
- Indications: probable cause to suspect isolate is involved in patient infection, uncertain susceptibility to antimicrobials
- Factors to consider: body site, presence of other organisms, quality of specimen, patient allergies
- AST standard elements: pure culture, logarithmic phase, standard inoculum, incubation, media, antimicrobial agents
- AST methods: Broth, Agar, Macrodilution, Disc Diffusion, Microdilution, Disk Gradient Agar Dilution
- Interpreting AST results: susceptible, intermediate, resistant
Agar Method: Disk Diffusion Test
- General steps: prepare 0.5 McFarland standard suspension, streak on Mueller Hinton Agar, add paper disk with antibiotic, incubate, measure zone of inhibition
- Result interpretation: obtain zone size, compare to established zone sizes, report susceptibility
- Multiple discs can be used on one plate, avoiding overlap
- Example: Disk Diffusion set up on S. aureus
Review and understand the flow of work in clinical microbiology labs from specimen collection to issuing reports. Topics include proper specimen handling, microscopic examinations, culture techniques, and identification methods.
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