Lab Report Example: Classification of the Unknown Bacterias

Introduction

Currently, there are 30,000 formally named bacteria species that are in pure culture. Bacteria are ubiquitous,  free-living organisms often consisting of one biological cell. When identifying them in laboratory characteristics such as gram staining, Endospore staining, motility, and isolation are used as identification and isolation methods. Bacterial isolation and identification are important in the medical industry to identify pathogens isolated from a patient. In microbial ecology, the identification of microorganisms helps characterize biodiversity.

The purpose of this study done in the lab was to use differential staining and microscopy to classify the selected unknown bacteria based on observing their morphology and cell structure. The goal was to demonstrate how to Gram staining, endospore staining, use MIO tubes, NA, EMB, and MSA plates to classify the unknown bacterias. 

A couple of the unknown bacteria it could have been are Escherichia coli or Staphylococcus aureus. E.coli is a gram-negative anaerobic that is rod-shaped. It does not have a nucleus or other membrane-enclosed organelles. It is most commonly found in the lower intestines of humans and animals. (Howard C. Berg, 2004) If a motility test is done the tube would be cloudy indicating the bacteria is motile. When E. coli is streaked on an EMB plate the bacteria will appear gold. S. aureus is gram positive cocci. It is frequently found in the upper respiratory tract and on the skin. ( Tracey A. Taylor and 2017) When gram stained it can be observed as violet under the microscope which indicates it is gram-positive. The S. aureus is also able to grow on MSA plates implies that it is a gram-positive bacteria. 

Materials and Procedures 

The unknowns that were tested were numbers 48 and 74. Gram staining was the first test that was run to show if the bacteria is gram-positive or gram-negative. A bacteria smear was prepared and first stained with crystal violet for 30 seconds. Then the slide was rinsed gently with water and once clean Gram’s iodine was added for another 30 seconds. Repeat rinsing after each chemical is added to the slide. Next was the acetone alcohol to decolorize and after rinsed safranin was added as a counterstain. Once the slide is dry it is observed under the microscope to discover the shape of the bacteria. The next test was to streak the bacteria on Petri plates for isolation. Unknown 48 was streaked on a mannitol salt agar plate (MSA) whereas 74 was streaked on an eosin methylene blue plate (EMB). The correct plates were chosen based on the shape and color of the bacteria under the microscope. From the NA plates, a tiny portion of the well-isolated bacterias was collected with a sterile loop and streaked using the quadrant streak technique on either the MSA or EMB plates. This test is important because gram positives can not grow on EMB plates and gram negatives can not grow on MSA plates so then the results showed it was streaked correctly if the bacteria grew.