: Bacterial Growth Characteristics

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


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