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Microbiology, Undergraduate, Lab Report, Quinnipiac University

  1. Read the task in Box 1.
  2. Download each of the pdfs and read them. Keep these open so you can refer to them as you watch the video.
  3. Watch the video.

Step 1

The Task

Microbiology, Undergraduate, Lab Report: ‘Identification of Indigenous Unknowns’, Quinnipiac University

Of the 1 x 1014 cells that compose our bodies, 90% of them are bacterial and only 10% (1 x 1013) are human.  This means that, when it comes to our bodies, bacteria truly are everywhere.  These bacteria make up our normal flora.  In the first week of Pathogenic Microbiology, a course for second, third and fourth year students, members of the laboratory swab three body sites (the back of the hand, the nares, and the back of the throat) and recover their normal flora on solid media.  Over the course of the next 14 weeks, the students must use the skills they have accrued in lab, material they have researched on their own, or material that I have given them, to characterize and identify at least three of the organisms that they have recovered.  At the end of the semester, the students submit a final lab report describing their methodologies and identification.  This lab report is intended to be written for an audience of clinical microbiologists and should reflect the best practices of the discipline in technique, content, and form.  Both the experiment and the report is intended to enable the students to use the material they have learned in lab to design, implement, and describe a logical plan for the identification of an unknown.  I believe that this assignment helps both to enhance critical thinking skills and to allow the students to explore microbiology content in a very personal way.  

Step 2


Indigenous Unknowns Lab Report


Normal flora, which make up about 90% of the cells of a human body, are microbes that live and grow on the body without causing disease under normal conditions. Many of these bacteria simply live on the body without harming or helping it, but many of the bacteria that inhabit the body can also protect us against other bacteria that may grow and cause disease. The purpose of this experiment was to swab the skin, nose, and throat to see what bacteria are present in each of these bodily environments, and then to choose three colonies and identify these bacterial species using a dichotomous key and a series of biochemical tests. The identification of normal flora can be beneficial in the case of an opportunistic infection. If one of the body’s own normal flora is given the right conditions, such as increased growth or a weakened immune system, it can cause an infection. In this case if an infection results from one of the body’s own flora, it may be necessary to identify the organism in order to decide which antibiotic to use. Each individual person has their own unique combination of microbes living on them as normal flora, but there are certain genera that are commonplace in certain body locations. Of the places that were observed in this experiment, the skin and the nose generally have the same genera. These species include Corynebacterium, Micrococcus, Staphylococcus, and Proprionibacterium. The bacteria in the throat are generally different from those on the skin because they live in a different environment under different conditions. These bacteria include Fusobacterium, Haemophilus, Lactobacillus, Neisseria, Staphylococcus, Veillonella, and the most common inhabitants of the oropharynx are species of the Streptococcus genus. In this experiment, a dichotomous key and biochemical tests were used to identify one species from each of the environments that were swabbed (1).

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Identification of Indigenous Unknowns


In a scientific field with so much genetic variation and rapidly evolving species, it has become increasingly difficult to correctly identify unknown microorganisms. With this increase in difficulty, we have also seen an increase in the importance of a correct identification. Because of the many different treatments needed to cure bacterial infections and diseases, it has become crucial that the organism affecting the patient be correctly identified so that the proper treatment can be prescribed. The experiment conducted was used to demonstrate this concept, and how a clinical microbiologist might go about properly isolating and identifying an unknown organism from various body sites. In addition to this objective, the experiment was also carried out to show just how colonized the human body is with bacteria, comprised of both normal microbiota and opportunistically pathogenic bacteria.

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Identification of Unknown Indigenous Bacteria


Many bacteria can be found in and on nearly all areas of the healthy human body.  These bacteria are referred to as normal flora and they for the most part live in commensal and mutualistic relationships with humans, often providing benefits such as aiding in digestion and preventing colonization by pathogenic bacteria (2).  Normal flora can also become parasitic and pathogenic given the necessary conditions, such as when one species is killed by antibiotics allowing another to establish a superinfection.  Different parts of the human body exhibit different types of normal flora.  The epidermis and nares are both commonly inhabited by Staphylococcus and Corynebacterium species while Streptococcus, Neisseria, and other Gram-negative cocci and bacilli are often found in the oropharynx (2).

The purpose of this experiment was to isolate, purify, and identify normal flora from the hand, nares, and oropharynx.

Materials and Methods

Swabs were taken of the hand, nares, and oropharynx and inoculated onto trypticase soy (TSA) and blood agar (BAP).  Many bacteria were found growing on swabs from each plate.  Well-isolated colonies were subcultured onto new TSA and BAP and then isolated and tested in an effort to determine their identity.  A colony of each isolated species was Gram-stained and subsequently further tested.

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Step 3

Step 4

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