Clinical Microbiology Lab Procedures Review

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Questions and Answers

What is the purpose of the anaerobic indicator strip used in the jar?

To turn the jar lid a different color when anaerobic conditions are achieved

To monitor the presence of oxygen in the jar (correct)

To test the ability of the GasPak system to create anaerobic conditions

To provide a catalyst for the anaerobic reaction

Which of the following organisms is able to grow in both microaerophilic and anaerobic conditions?

Pseudomonas aeruginosa

Staphylococcus aureus (correct)

Clostridium perfringens

Campylobacter jejuni

What is the purpose of the paper sachet that is placed in the jar?

To absorb any excess moisture that builds up inside the jar

To test the ability of the GasPak system to create anaerobic conditions

To provide a catalyst for the anaerobic reaction

To create an oxygen-free environment inside the jar (correct)

Which of the following organisms is able to grow in aerobic conditions but not in anaerobic conditions?

Pseudomonas aeruginosa Signup and view all the answers

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 Signup and view all the answers

Which of the following organisms is able to grow in microaerophilic conditions but not in anaerobic conditions?

Campylobacter jejuni Signup and view all the answers

What is the primary objective of the four-quadrant streaking method?

To quantify the number of colonies present Signup and view all the answers

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 Signup and view all the answers

Which of the following is the BEST approach to interpreting broths during result interpretation?

Look for the presence of turbidity throughout the broth Signup and view all the answers

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 Signup and view all the answers

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 Signup and view all the answers

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 Signup and view all the answers

What technique is used to observe true motility of an organism?

Wet mount preparation Signup and view all the answers

Which step in the Gram staining procedure decolorizes gram-negative bacteria?

Decolorizer application Signup and view all the answers

What is the primary purpose of using selective media in microbiology?

To inhibit the growth of unwanted microorganisms Signup and view all the answers

Which media used in Lab 7 could be classified as both selective and differential?

MacConkey (MAC) Agar Signup and view all the answers

What is the primary reason for overdecolorization during the Gram staining procedure?

Excessive decolorizer application Signup and view all the answers

Based on the Lab 7 results, which statement is correct?

One organism was gram-positive, and the other was gram-negative Signup and view all the answers

Which of the following is NOT a factor to consider when performing antimicrobial susceptibility testing (AST)?

The patient's age and gender Signup and view all the answers

What is the purpose of performing antimicrobial susceptibility testing (AST) on an isolate?

Both (a) and (b) Signup and view all the answers

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 Signup and view all the answers

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 Signup and view all the answers

Which of the following is NOT a method for antimicrobial susceptibility testing (AST)?

Antibiotic gradient electrophoresis Signup and view all the answers

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 Signup and view all the answers

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. Signup and view all the answers

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. Signup and view all the answers

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. Signup and view all the answers

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. Signup and view all the answers

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. Signup and view all the answers

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. Signup and view all the answers

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

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Description

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.