How did the test results lead to identification? What problems were encountered, if any? In this section, you should also include 1-2 paragraphs of background information on each bacterium you identified, including its characteristics and significance.

GENERAL:
Unknown reports in microbiology are written in scientific format. Scientific writing is different
from other types of writing in that the results of the exercise or experiment are being showcased,
not the writing. The purpose of scientific writing is not to entertain, but to inform. The writing
should be simple and easy to understand. There is a specific style that must be followed when
writing scientific reports. Scientific writing is typically written in the passive voice. The pronouns
“I”, “We” and “They” are not used. For example, instead of writing “I used a TSA agar plate to
isolate my unknown,” it is customary to write, “A trypticase soy agar (TSA) plate was used to
isolate the unknown.” It is also customary to write in the past tense for most of the report. This
includes the introduction, the summary, the description of the materials and methods, and the
results. The present tense is reserved for the conclusions about the results.
Microbial nomenclature: The name of the bacterium should be written out and spelled correctly.
The name should be italicized, e.g. Staphylococcus aureus. The genus is capitalized but the
species is not. After the full genus name is given in the paper, it can be abbreviated as S. aureus,
but it is still italicized. This is as long as there is no other genus in the paper that starts with the
same letter. (For example, if you have a Staphylococcus species and a Salmonella species as your
unknowns, you cannot abbreviate!)
MECHANICS: The lab report should be typed using a 12-point normal font such as Times New
Roman or Arial, and should be single-spaced. Your instructor will notify you as to whether you
are to submit the report electronically in Canvas or on paper. If submitting a paper copy of the
lab report, it should be presented bound in a report folder. Reports will be graded on content as
well as spelling, grammar, punctuation, and organization.
SECTIONS OF THE UNKNOWN LAB REPORT:
(Note: Other than the title page, the pages of the report must be numbered)
TITLE PAGE
The title page should include the following information:
UNKNOWN NUMBER
YOUR NAME
DATE (the due date)
LAB INSTRUCTOR’S NAME
COURSE NAME / SECTION NUMBER
SEMESTER / YEAR
INTRODUCTION
This section introduces the reader to the study and why the study was done. This should only be
a few sentences long. Example: “There are many reasons for knowing the identity of
microorganisms. The reasons range from . . .[explain 2-3 reasons why you may want to identify
an unknown bacterium]. This study was done by applying all of the methods that have been
learned in the microbiology laboratory class for the identification of an unknown bacterium.”
Cain et al 136 Fall 2021
MATERIALS & METHODS
This is where the details of the study are listed. The materials and methods section should contain
four paragraphs: (1) a description of how the three unknowns were separated and isolated, (2)
a description of the identification of the Gram-positive Streptococcus/Enterococcus isolate, (3) a
description of the identification of the Gram-positive Staphylococcus isolate and (4) a description
of the identification of the Gram-negative isolate. Be specific, but concise: do not rewrite the
lab manual! The most common way is to mention the names of the materials used and why they
were used, and to reference the lab manual for the procedure or method.
See example 1.
Example 1: “An unknown labeled number 37 was selected. The methods that have been learned
in microbiology laboratory were applied to identify this unknown. Procedures were followed as
stated in the course laboratory manual (Cain et al, 2020) unless otherwise noted. The first
procedure that was performed was streaking the unknown out on a TSA plate, using the T streak
method described in the lab manual. This was done in order to . . . [explain why]. After the plates
were incubated and grown, the morphology was observed and recorded, and a Gram stain was
performed. After determining the Gram reaction, specific biochemical tests were performed. The
biochemical tests were chosen from the lab manual. Since unknown 37 was determined to be a
Gram-positive rod, an endospore stain was also performed. The following types of media were
inoculated with unknown 37: starch, lipid, and casein agars, mannitol salt agar, a gelatin deep, a
bile esculin agar slant, and a nitrate broth. Table 1 lists the test, purpose, reagents and media
components, and results.”
RESULTS
This is where the results are summarized. The results should be presented in 3 tables, using a
separate table for each unknown, i.e. one table for your Gram-positive Staphylococcus, a second
table for your Gram-positive Streptococcus or Enterococcus, and third table for your Gramnegative (see example below). This is also where the flow charts showing how you arrived at your
answers are presented. The flow charts included in the report should trace the route you
followed on your flow chart to identify your unknown. A short paragraph explaining how the
results are presented should also be included. Example: “Unknown 37 appeared as a large,
mucoid, cream-colored colony on the nutrient agar plate. A Gram stain revealed that the
organism was a Gram-positive rod, and an endospore stain demonstrated the presence of
subterminal endospores. A stock of unknown 37 was grown on a nutrient agar slant and used to
inoculate the tests listed in Table 1. The results of all tests are presented in Table 1 and shown
in flow chart form.”
Cain et al 137 Fall 2021
Table 1: Gram-positive Bacillus Identification
Test Purpose Media
Components
/Reagents
Observations Results Interpretations
Gram
Stain
Determine cell
wall properties
Crystal violet,
iodine, alcohol,
safranin
Purple rods Grampositive
rods
Organism has thick
peptidoglycan layer, no
outer membrane
Endospore
Stain
Determine if
spore
producer
Malachite green,
safranin
Pink rods with
small green
endospores
between the
center and the end
Positive
for spore
formation
Organism produces
endospores
Starch Determine if
organism can
hydrolyze
starch
Starch in plates
Added iodine after
incubation
Zone of clearing Positive Organism has enzymes
maltase and amylase
needed to hydrolyze
starch
Lipid Determine if
organism can
hydrolyze
lipids
Tributyrin in plates No zone of clearing Negative Organism does not
possess lipases and
cannot hydrolyze lipids
Gelatin Determine if
organism can
hydrolyze
gelatin
Gelatin in tubes Tube was still solid
after incubating
Negative Organism does not
produce gelatinase
Cain et al 138 Fall 2021
FLOWCHART: UNKNOWN #37 (GRAM-POSITIVE)
Starch (positive)
Casein (positive)
Bile Esculin (positive)
Gram Stain
Gram-positive rod
Endospore stain (positive)
MSA Growth (negative)
Positive Negative
B. brevis
B. licheniformis
B. polymyxa
B. sphaericus
B. cereus
B. coagulans
B. megaterium
B. subtilis
Positive Negative
B. brevis
B. lichniformis
B. polymyxa
B. sphaericus
Positive Negative
B. lichniformis B. brevis
B. polymyxa
Positive Negative
B. polymyxa B. lichniformis
Nitrate (positive)
Lipid (positive)
B. polymyxa
B. polymyxa
Unknown #37 = Bacillus polymyxa
Cain et al 139 Fall 2021
DISCUSSION / CONCLUSION
This section interprets the meaning of the results. Again, you should have a separate paragraph
for each identified isolate. The following questions should be answered here:
How did the test results lead to identification? What problems were encountered, if any? In this
section, you should also include 1-2 paragraphs of background information on each bacterium
you identified, including its characteristics and significance.
Example of a discussion: “After several differential tests, it was concluded that the Gram-positive
organism in unknown 37 was Bacillus polymyxa. After performing the Gram stain, it was
determined that the unknown was a Gram-positive rod. The results of the endospore stain
showed that the organism produced subterminal endospores, indicating it belongs in the genus
Bacillus. The organism was grown on a TSA slant for use in inoculating the rest of the biochemical
tests. All of the biochemical tests worked well except for the test for gelatin hydrolysis. It gave a
false negative result at first, which was inconsistent with the rest of the results. Using the Bacillus
identification dichotomous key, it was concluded that the unknown was Bacillus polymyxa
Bacillus polymyxa is a Gram-positive endospore-forming bacillus (Bauman, 2006). It is a
motile bacterium, and possesses peritrichous flagella (Todar, 2005). B. polymyxa can be found
in a wide range of environmental habitats, including acidic environments. It is commonly found
in soil, water, and decaying vegetables (Stedman, 2006). Because it can grow in both moderate
and cold temperatures, B. polymyxa is classified as a psychrotroph. B. polymyxa produces a thick
polysaccharide capsule, and is also a facultative anaerobe (Todar, 2005). Although B. polymyxa
does not cause disease in animals or humans, it is of medical significance because it produces the
antibiotics polymyxin and colistin (Madigan and Martinko, 2006).
REFERENCES:
Note: the minimum number of references is three, which can include the lab manual and the
textbook. You may not use wikis (such as Wikipedia or MicrobeWiki) as sources! References
should be listed in APA format, and parenthetical in-text citations must be used where
appropriate.
Note: Any information presented that is not your original idea or your own data must be
credited with an in-text citation!
Use this format to cite the lab manual on your Works Cited page:
Cain, D., Hanks, H., Weis, M., Bottoms, C., and Lawson, J. (2021) Microbiology Laboratory
Manual, Summer 2021. Collin College, Plano, TX.
The corresponding in-text citation would be (Cain et al., 2021).
UNKNOWN WORKSHEET
Attach your completed unknown worksheet.
Modified from:
http://www.sci.sdsu.edu/classes/biology/bio210/lab/demers/Howtowriteanunknownlabrepor.
pdf

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