BIO244 General Microbiology Identification of an Unknown Bacterial Culture Laboratory Report Format Guide
Guidelines for Writing the Formal Science Laboratory Report
The scientific paper for the bacterial unknowns should have the following sections: Title, Introduction, Materials and Methods, Results, Discussion, Conclusion and Literature Cited. The actual words “Introduction”, “Materials and Methods”, “Results”, “Discussion”, “Conclusion”, and “Literature Cited” should be underlined or appear in bold, left justified, and used to head the sections of the paper. Sections of the paper should run continuously with a space between each as shown below, not on separate pages. Throughout the whole narrative of the report do not use pronouns (e.g. I, we, they), instead use the third person descriptive style. For example, instead of writing “I used a blood agar plate,” write, “A blood agar plate was used.” Aspects of the experiment should be discussed in past tense; you already did it and need to write about it from that perspective. The language used should be formal and the report should be written for a broad audience who is not likely to be familiar with this particular experiment, but you can assume some level of basic biology class knowledge. Remember to use the proper italicized binomial nomenclature for the names of the organisms. The report should be typed, double spaced, with 12-point font and one inch margins. Your name, the submission date, and course section number should appear in the upper left corner of the first page above the title. The pages should be numbered on the bottom sequentially beginning with the first page. No cover pages or report covers of any kind should be included. Citation of reference sources should be done in the “CSE name-year system” style (Last name Year of publication) and the source should appear in the Literature Cited section using proper CSE format for scientific publications.
Title The title should succinctly describe the specific analysis or study that is being conducted, for example: “Guidelines for Writing a Science Laboratory Report”. The title should appear centered at the top of the paper on the first page with all words that are not articles or prepositions (a, an, the, and, on, of, for, etc.) beginning with a capital letter.
Introduction In this section, briefly describe the experiment. State a hypothesis (an “if then” statement that may require multiple sentences) that is clear and appropriately addresses the purpose of this laboratory exercise. For example “If the collective results of a profile of key biochemical assays are compared to the known results for limited subset of bacterial species, then a specific unknown culture from that subset of bacterial species can be correctly identified based on the results obtained from the biochemical assays.” (Write your own: do not plagiarize this one!) Give background information regarding the experiment and discuss why this experimental topic is of interest. Be sure to include general characteristics of bacteria, and the global significance of bacteria and bacterial identification. Describe in a general sense the types of tools used in the culturing and identification of bacteria and include an explanation of why different media are used to assay for different enzyme production by microorganisms and how the results are important to the identification process. Reference sources are required and must be cited appropriately. Weave your introduction into a cohesive flow that tells a story to the audience about bacteria and why researchers find it important to identify them. Avoid simply listing disjointed quotes. The introduction is an essay, not a bulleted list, and should tell the audience a story about bacteria, identification, and the purpose of your experiment. Other than the hypothesis statement and explanation of the experiment, all the factoids that you weave together in this section should be cited; they are facts you collected from various sources to tell your story, not creative writing. If you outline a good story and cover all the key
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points mentioned, this section is likely to be three plus pages long. Do not worry if it is “too long”. Be concerned if it is too short. This is the only real creative part of the scientific paper and length will vary depending on your own personal style. A minimalist should still have about three pages if all required aspects are covered.
Materials and Methods This section is used to describe the materials and methods employed during the key laboratory exercise experiments. Include only the bare minimum key assays that were necessary to solve your unknown; these are the ones listed on your dichotomous key in the path to your organism. In cases where multiple assays were employed to determine one characteristic, only one type of assay need be presented. The four or five assays that appear here will be the same ones that you present in the Results and Discussion sections of this paper. For the Materials and Methods section describe each essential assay separately in a separate paragraph. Begin each description with a brief statement of the characteristic or characteristics the particular media or staining procedure is examining but do not explain how it all works; that belongs in the Discussion section. Include the name (e.g. MacConkey Agar, Tryptone Broth, etc.) and type (e.g. defined, complex, differential, selective) of media used to grow the organism and list any reagents or indicators (e.g. Phenol red, iodine, etc.) that are either present in the media or that had to be added following incubation or used for staining in order to be able to visually score the results. Indicate how the media was inoculated and the time and temperature of incubation, or how the staining procedure was performed. Do not include the enzymatic reactions here: save those for the Discussion. Keep in mind that this section should be written like the instruction paragraph of a cookbook: it is a ‘how to’ for the experiments you performed. Include the lab manual in the Literature Cited section and cite it for each procedure as it was the source of your directions.
Results Create a data table for the organism in which to display the results of the necessary and relevant biochemical tests and observations used in the exploration and identification of the unknown culture. Include only the key assays you described in Materials and Methods, not every test that was performed. Only the observed outcome and basic results of the experiments should be described in the table. Interpretation of the data regarding the full meaning of the observations or enzymatic reactions and their use in identification of the unknown should instead be included in the Discussion section. The Results table should contain column headings for the following categories: 1. “Assay/Characteristic” in which you name the characteristic you are assaying your unknown for with the staining procedure or media being employed, such as “Gram Stain Reaction” or “Lactose Fermentation”. 2. “Media/Source” in which you state the name of the medium being used to assay the particular characteristic (e.g. MacConkey agar) or the source material for the procedure (e.g. heat fixed smear). Keep in mind that some media can be used to assay multiple characteristics and should be listed separately for each characteristic in the chart. For example, MacConkey agar can be used to determine both Gram reaction and lactose fermentation but list those two aspects separately. 3. “Observations” in which you state the appearance of the organism or media upon completion of the procedure. This is the result you observed (e.g. pink), not an interpretation of what that visual appearance means (e.g. positive for lactose fermentation). 4. “Results” in which you state the outcome indicated by the media or staining procedure. For example: “Positive for indole production” or “Gram negative”. The result indicated here should only be the obvious meaning of the observation you made. The complete interpretation of the observations and results, including the enzymes produced, reactions completed, or cellular characteristics being observed, should instead appear in the Discussion section.
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Example: Table 1: Assay Results for Unknown #1 Assay/Characteristic Media/Source Observations Results Gram Stain Reaction Heat fixed smear Pink single coccobacilli Gram negative
Gelatinase Production Nutrient Gelatin Stab Solid Gelatinase negative Lactose Fermentation Lactose Broth with Durham Tube Yellow media with bubble in Durham tube Positive for lactose fermentation to acid with gas production Indole Production Tryptone Broth Red superficial layer Positive for indole production As a general rule, tables must each be titled with the word “Table” and an appropriate succinct description of their contents as the title, and are numbered sequentially. Tables should be inserted into the body of the document where appropriate but should not be allowed to break across pages. Pictures, drawings, dichotomous keys, and any other visuals that are not tables should be titled “Figure” and given an appropriate succinct title similarly indicating the contents. Figures are also numbered sequentially in order of mention in the text, and attached in sequential order, either within the text or as separate pages close to the text they accompany.
Discussion In a narrative written form, give the interpretations of the results of each assay. Discuss only the assays for which you presented results in the table in the Results section and explained in the Materials and Methods section. Keep in mind that chemical reactions being performed by living organisms have substrates being acted upon by enzymes resulting in the production of a product, and that determination of this product production is usually done through a color change reaction that occurs between the metabolic reaction product and some kind of indicator in the media. List these enzymes, substrates, products, and color change reactions in narrative form. Explain what each possible result would look like and state what result you observed for your organism. Discuss each assay in a separate paragraph. For example: “MacConkey agar is both a selective and differential medium. It contains bile salts, crystal violet, and sodium desoxycholate to inhibit the growth of Gram-positive organisms, which have a thick exterior peptidoglycan wall, while allowing the growth of Gram-negative organisms, which have a thin peptidoglycan wall covered by an outer membrane (Author Year). Growth of unknown organism #1 on MacConkey agar thus indicates that this organism is Gram-negative. Additionally the plate contains lactose and the pH indicator neutral red. For organisms that are capable of growth on this media, lactose fermentation ability can be determined. Organisms that are capable of producing the enzyme betagalactosidase can hydrolyze lactose into monosaccharides (Author Year). When the resulting monosaccharides are fermented into acid, the pH indicator in the media will turn from colorless to hot pink. Colonies of organisms that do not ferment lactose will appear colorless or pale pink (Author Year). Unknown culture #1 produced hot pink colonies on the MacConkey agar thus indicating that it is positive for lactose fermentation.” Be sure to include citations for any and all sources used. Do not discuss aspects of an assay that do not have direct bearing on the organism being discussed. For example, failure of an organism to grow on MacConkey agar indicates that it is Gram-positive. If the organism fails to grow, the lactose fermentation ability of the organism cannot be assessed on this medium and thus the differential capabilities of the media should not be discussed with respect to this organism.
Conclusions The purpose of this section is to evaluate or analyze the results and determine the identification of the unknown based on the collective results. Present your results and interpretation of them as an ordered flow of
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logic. Indicate what result you needed to have first to initially narrow the list of possible organisms and how this result led you to seek the results of the next assay and so on until the inevitable conclusion of the identity of your unknown. Discuss the analysis from a general perspective on how you would go about identifying any of the potential unknown organisms from the list of possible organisms for this activity using the least number of assays. Describe which experiment you would need to perform first and why and so on. Generate and include as a figure a dichotomous key to visually display the logic flow, and then write a description to walk though and explain the key. Refer to the key by figure number in the text. Explain how the first experiment would divide the list of possible unknowns into two categories. Then within each of those categories explain which experiments and results are important to dividing the organisms into smaller and smaller groups until the individual organism is identified. The explanation should address all the possible organisms utilized for this laboratory activity and how you would go about solving the identity of each one separate from all others. Your explanations of the logic flow should give a clear indication that you could apply the experimental logic to any organism you might theoretically be given from the narrow list of possible unknown organisms employed in this activity. Keep in mind that “Di” means two and thus your key should only have one characteristic at each branch with only two choices (e.g. positive or negative) from that point on the key. Also remember to have all the organisms that are keyed out line up across the bottom of the figure, all on the same horizon line in the chart. The names can be turned sideways but the first letter of each must start on the same elevation line. Do not forget to label your key with a figure number and title.
Literature Cited List here all source material cited in the laboratory report. Use proper CSE format for scientific publications including listing the sources in this section in alphabetical order by the first author’s last name. The SCCC Library web resources can be of great assistance in both citation style and in locating potential sources. For a full explanation of CSE documentation systems see:https://bcs.bedfordstmartins.com/resdoc5e/ under the pink sciences section. The in text citations throughout the paper are to be done in the CSE name-year system. Note: there is no limit on the number of sources necessary. At a minimum your textbook and lab book should serve as sources throughout the report. You may NOT cite the laboratory supplemental packet as an official source. Instead find the information in an independent copy written source for use in your report.
Book: After the author(s) and title, give the place of publication, the name of the publisher, and the date of publication. *Note the first and middle initials and limited use of punctuation with authors, and lower case letters in the title!
Tortora GE, Funke BR, Case CL. Microbiology an introduction. 9th ed. New York (NY): Pearson Benjamin Cummings; 2007.
Journal article: After the author(s) and the title of the article, give the journal title, the year, the volume number, the issue number if there is one (in parentheses), and the page numbers on which the article appears.
DeMarini DJ, Adams AE, Fares H, De Virgilio C, Valle G, Chuang JS, Pringle JR. A septin- based hierarchy of proteins required for localized deposition of chitin in the Saccharomyces cerevisiae cell wall. J Cell Biol. 1997;139:75–93.
Although you may use internet-based sources, do not use random web pages. Instead use electronic encyclopedias, data bases, journals and books. Cite these sources as if you had the paper version. For scientific papers, it is best to focus on primary sources. In general, if the source does not have an author clearly listed it is not appropriate for a scientific paper.
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