Lab Exercise: Bacterial Growth Characteristics
Purpose and Learning Outcome
After completing this exercise, you should (1) be aware that certain bacterial species have unique growth patterns on certain growth media, (2) be able to identify some bacterial species based on their unique growth patterns, (3) be practiced at categorizing bacterial species according to their oxygen requirements, and (4) be practiced at interpreting blood agar results.
The skills/abilities listed above are important because they can be used to help identify bacterial species.
Required Materials and Equipment
A device with internet access
Instructions for Part 1: Growth Characteristics on TSA
In the table below, click on the name of each bacterial species to see a photo of what it looks like when grown on a TSA plate for 24 hours at 37 degrees C (unless otherwise noticed). After viewing each photo, fill out the two columns to the right of the species name.
Non-unique (common) growth on a TSA plate looks like this. If a bacterial species has an obviously different color and/or texture than that when growth on a TSA plate, then consider it unique.
Bacterial species Unique growth characteristics when grown on TSA plate?
Y or N If the species has unique growth characteristics on TSA, then describe them. If the species has no unique growth characteristics, then you do not have to type anything in this column.
Alcaligenes faecalis
Bacillus cereus
Bacillus megaterium
Bacillus mycoides
Bacillus subtilis
Citrobacter freundii
Corynebacterium xerosis
Enterobacter aerogenes
Enterococcus faecalis
Escherichia coli
Klebsiella pneumoniae
Micrococcus luteus
Micrococcus roseus
Moraxella catarrhalis
Mycobacterium smegmatis
Neisseria sica
Proteus mirabilis
Proteus vulgaris
Pseudomonas aeruginosa
Salmonella typhimurium
Serratia marcescens (growth at room temp)
Serratia marcescens (growth at 37 degrees C)
Staphylococcus aureus
Staphylococcus epidermidis
Streptococcus salivarius
Instructions for Part 2: Interpreting blood agar results
View these photos of different bacteria grown on TSA plates containing 3% sheep’s blood. All the plates in the photos were growth at 37 degrees C for 24 hours. After viewing the photos, complete the table below. Hint: The 3 species in the table below all show different types of hemolysis. For help, you can read through p. 6 of the Lab Exercise on Selective/Differential Media and/or view this video tutorial on how to interpret blood agar results.
Column A:
Bacterial species Column B:
Type of hemolsyis (alpha, beta, or gamma)? Column C:
Explanation for your answer to Column B
Enterococcus faecalis
Staphylococcus aureus
Staphylococcus epidermidis
Instructions for Part 3: Determining oxygen requirements for bacteria
Here are 4 different bacterial species grown on a TSA plate at 37 degrees C for 24 hours in the presence of oxygen.
Here are the same 4 bacterial species grown in the absence of oxygen (i.e. grown inside a Gas Pak).
After viewing the photos linked above, fill in the table below. For help, you can read pp. 3-6 of the Lab Exercise on Bacterial Growth Characteristics and/or view this video tutorial on how to interpret Gas Pak results.
Column A:
Bacterial species Column B:
Oxygen requirement (obligate aerobe, obligate anaerobe, facultative, aerotolerant, or microaerophile) Column C:
Explanation for your answer to Column B
Micrococcus luteus
Clostridium sporogenes
Enterococcus faecalis
Staphylococcus epidermidis