Identification of Unknown Organism B as Staphylococcus aureus Through Systematic Biochemical and Morphological Analysis
Overview
This lab report documents the systematic identification of an unknown bacterial organism through Gram staining, selective/differential media plating, and comprehensive biochemical testing over four laboratory sessions. The investigation successfully identified Unknown Organism B as Staphylococcus aureus based on cumulative test results including Gram-positive cocci morphology, catalase positivity, salt tolerance, and characteristic biochemical reactions.
What this lab report covers
- Introduction: hypothesis that unknown organism could be identified to species level using biochemical profiling
- Materials and Methods: comprehensive list of selective media, differential media, and biochemical tests performed with standardized incubation conditions
- Results: tabulated findings from selective/differential plating and enzymatic/biochemical tests confirming S. aureus identification
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Lab Report
Introduction
The identification of unknown bacteria is a foundational exercise in microbiology, linking morphological observation with physiological and biochemical characterization. This investigation aimed to identify Unknown Organism B through a systematic series of tests conducted over four laboratory sessions (Labs 9–12). The hypothesis was that the organism could be identified to species level by matching its cumulative biochemical profile against established reference data (Tortora et al., 2019). Based on the results obtained, Unknown Organism B was identified as Staphylococcus aureus, a Gram-positive, catalase-positive coccus and a leading human pathogen responsible for infections ranging from minor skin conditions to life-threatening bacteremia and toxic shock syndrome.
Materials and Methods
The unknown was subjected to: Gram staining; selective and differential plating on Phenyl Ethyl Alcohol (PEA), Eosin Methylene Blue (EMB), Mannitol Salt Agar (MSA), and Blood Agar Plate (BAP); aerotolerance testing in Thioglycolate Broth; and a full biochemical panel including Phenol Red sugars (glucose, lactose, sucrose), Litmus Milk, Urea Broth, Tryptone Broth, Nutrient Gelatin, SIM Tube, Peptone Iron Agar, Phenylalanine Agar Slant, Starch Agar, Spirit Blue Lipid Agar, Triple Sugar Iron Agar (TSIA), Simmon’s Citrate, Nitrate Broth, and MRVP tubes. Catalase and Oxidase tests were performed on Nutrient Agar plates. All cultures were incubated at 37°C for 24–48 hours.