D311 Task 2: Identifying Unknown Microorganisms in Lab 9

D311 Task 2: Identifying Unknown Microorganisms in Lab 9

Student Name

Western Governors University

D311 Microbiology with Lab: A Fundamental Approach

Prof. Name:

Date

MICROBIOLOGY WITH LAB: A FUNDAMENTAL APPROACH

Task 2: Unknown Lab Manual 9

The objective of Task 2 in this microbiology lab is to identify an unknown bacterial organism using a minimal number of laboratory instruments and tests, simulating real-world constraints. This process emphasizes problem-solving skills by encouraging learners to analyze provided lab evidence, make informed decisions about subsequent tests, and ultimately confirm the organism’s identity. The exercise aims to develop critical thinking, analytical reasoning, and decision-making capabilities, which are essential for connecting complex biological systems during microbial identification.

Task Instructions

Welcome to the Unknown 9 Lab! Your task is to apply various laboratory tests strategically to identify an unknown bacterial species. Prior to starting, ensure you have selected the correct organism group corresponding to the initial letter of your last name. Given the typical limitations of lab resources and time, not every test should be performed on every sample. Use the provided decision tree to guide your selection of diagnostic tests, narrowing possibilities until a final identification is reached.

In your lab report, focus your discussion on the Gram stain and two other tests chosen based on your results and decision tree guidance. Justify your choice for each test within the report. Upon identification of the organism, you will interpret the results of the Kirby-Bauer antibiotic sensitivity test to recommend an appropriate treatment option.

Investigation Tools

• Review Section 4, Lesson 2 for background on Gram staining and to familiarize yourself with the decision tree that will guide test selection.

• Save your lab report as a Word document titled: D311 Task 2 Lab Report [Last Name].

• Clearly indicate the unknown organism number you are identifying to avoid delays in evaluation.

Lab Procedure Overview

1. Initial Step: Gram Stain
   Start identification by performing a Gram stain to classify the bacterium as Gram-positive or Gram-negative. Observe the morphology to determine if the cells are bacillus (rod-shaped) or coccus (spherical).

   Guiding Questions:

   Question	Answer
   Is the organism Gram-positive or Gram-negative?	Provide justification based on staining color and cellular structure.
   What is the morphology of the organism?	State whether it is bacillus or coccus and support with visual evidence.

2. Next Test Selection
   Based on Gram stain results and the decision tree, choose the next test. This choice should be purposeful, considering the evidence from prior tests. The decision tree includes options such as endospore staining, catalase, glucose fermentation, citrate utilization, blood agar hemolysis, capsule staining, motility, lactose fermentation, Voges-Proskauer, coagulase, and Kirby-Bauer antibiotic testing.

Detailed Tests and Interpretations

Endospore Stain

This test reveals whether the organism produces resistant spores. The presence of spores is indicated by distinct coloration in the staining process.

Capsule Stain

Capsule staining identifies the presence of a polysaccharide capsule surrounding the bacterium, visible as a clear halo around the cell.

Blood Agar Growth and Hemolysis

This test assesses bacterial growth on blood agar and hemolytic activity, classifying hemolysis into alpha (partial), beta (complete), or gamma (none).

Citrate Test

This assay determines if the bacterium can utilize citrate as a carbon source, typically indicated by a color change in the medium.

Voges-Proskauer Test

This test detects acetoin production, a metabolic byproduct, with positive results indicated by a color change in the reagent tube.

Glucose Fermentation Test

This test evaluates the organism’s ability to ferment glucose, with gas production often noted as a secondary indicator.

Lactose Fermentation Test

Similar to glucose fermentation, this test assesses lactose utilization and gas production.

Catalase Test

Catalase activity is demonstrated by bubbling when hydrogen peroxide is applied, indicating breakdown of peroxide.

Coagulase Test

This test detects the enzyme coagulase, which causes clot formation in plasma.

Motility Test

Motility testing observes whether bacterial growth is diffuse (motile) or confined (non-motile).

Kirby-Bauer Diffusion Test

This antibiotic sensitivity test determines the susceptibility of the organism to specific antibiotics. Results categorize the organism as resistant, intermediate, or susceptible, guiding therapeutic decisions.

Summary

In a clinical microbiology context, the identification of unknown bacterial organisms requires a strategic, stepwise approach using key laboratory tests selected through evidence-based decision-making. Starting with the Gram stain, the use of a decision tree helps streamline testing, conserving resources while enhancing diagnostic accuracy. The Kirby-Bauer test further assists in selecting appropriate antimicrobial therapy, completing the diagnostic and treatment planning cycle.

References

• Western Governors University. (n.d.). Microbiology with Lab: A Fundamental Approach. Task 2 Unknown Lab Manual.

• Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock Biology of Microorganisms (15th ed.). Pearson.

D311 Task 2: Identifying Unknown Microorganisms in Lab 9

• Cappuccino, J. G., & Welsh, C. T. (2017). Microbiology: A Laboratory Manual (11th ed.). Pearson.