Microbiology 101 provided my first exposure to live bacterial cultures in college (aside from those my roommates created in our minifridge). The distinct smell of an Escherichia coli culture, the unique green coloration of a fuzzy penicillium colony and the many failed attempts at lighting my Bunsen burner are fond memories of the experiences that hooked me on microbiology.
The fundamental microbiology laboratory skills I learned during basic courses such as aseptic transfer, streaking for isolation, staining techniques, bright-field microscopy, differential testing and execution of biochemical assay have held true and helped me throughout my career.
What strains should educators use in their classes to demonstrate these basic skills, reactions and methods? We have some suggestions. The list below can help educators choose the best strains for teaching their microbiology students. We’ve included a brief description of each strain, a few key reactions or skills they can demonstrate, and products formats we recommend for students.
All strains are a low biosafety level (1 or 2) to ensure safe handling by young microbiologists.
1. Staphylococcus aureus
| Biosafety Level | 2 |
| Morphological Characteristics | Beta-hemolytic on Sheep’s Blood agar plates |
| Staining Technique | Gram stain: Gram-positive cocci occurring singly, in pairs, or in irregular clusters |
| Biochemical Responses |
|
| Example Strain | ATCC 25923 |
| Formats Available |
2. Staphyloccocus epidermidis
| Biosafety Level | 1 |
| Morphological Characteristics |
|
| Staining Technique | Gram stain: Gram-positive usually in pairs and tetrads |
| Biochemical Responses | Coagulase (rabbit plasma-tube): Negative |
| Example Strain | ATCC 12228 |
| Formats Available |
3. Escherichia coli
| Biosafety Level | 1 |
| Morphological Characteristics | Deep pink colonies with surrounding pink precipitate (+ Lactose Fermentation) on MacConkey Agar |
| Staining Technique | Gram stain: Gram-negative straight rod |
| Biochemical Responses |
|
| Example Strain | ATCC 8739 |
| Formats Available |
4. Proteus mirabilis
| Biosafety Level | 2 |
| Morphological Characteristics |
|
| Staining Technique | Gram stain: Gram-negative straight rod |
| Biochemical Responses | Oxidase (Kovacs): Negative |
| Example Strain | ATCC 29245 |
| Formats Available |
5. Mycobacterium smegmatis
| Biosafety Level | 1 |
| Morphological Characteristics | Small to medium, circular to irregular, flat, erose edge, dull and rough, translucent, cream turning yellow/orange with age |
| Staining Technique |
|
| Biochemical Responses | Catalase (3% Hydrogen Peroxide): Positive |
| Example Strain | ATCC 14468 |
| Formats Available |
6. Pseudomonas aeruginosa
| Biosafety Level | 2 |
| Morphological Characteristics |
|
| Staining Technique | Gram stain: Gram-negative rod, straight or slightly curved |
| Biochemical Responses |
|
| Example Strain | ATCC 27853 |
| Formats Available |
7. Candida albicans
| Biosafety Level | 1 |
| Morphological Characteristics | Small to medium, white, circular, convex, dull colonies on Potato Dextrose agar |
| Staining Technique | Gram stain: Gram-positive, ovoidal, budding yeast cells |
| Biochemical Responses |
|
| Example Strain | ATCC 10231 |
| Formats Available |
8. Peniciliium rubens
| Biosafety Level | 1 |
| Morphological Characteristics | Rapid growth of downy white colonies that turn yellow then gray/green and yellow on the underside |
| Staining Technique | Lactophenol blue stain: Hyaline septate mycelia that produce hyaline conidiophores. The conidiophores branch into brush-like penicillus. Spores are borne in long chains from terminal sterigmata. |
| Biochemical Responses | Produces penicillin |
| Example Strain | ATCC 9179 |
| Formats Available |
9. Streptococcus pyogenes (Group A)
| Biosafety Level | 2 |
| Morphological Characteristics | Two colony types on Sheep’s Blood agar:
|
| Staining Technique | Gram stain: Gram-positive cocci |
| Biochemical Responses |
|
| Example Strain | ATCC 19615 |
| Formats Available |
10. Streptococcus agalactiae (Group B)
| Biosafety Level | 2 |
| Morphological Characteristics | Small, white to gray colonies with beta-hemolysis on Sheep’s Blood Agar |
| Staining Technique | Gram stain: Gram-positive cocci in short to long chains |
| Biochemical Responses |
|
| Example Strain | ATCC 12386 |
| Formats Available |
Download our Microorganisms for Education document to see more strains you may want to consider using during your microbiology courses.
Microbiologics also offers Parasite Suspensions and QC Microbiology Slides for education. Visit microbiologics.com to find the right strain and format for your classroom.
Thanks for the information.