How do you know if molds or bacteria that you have cultured in a petri dish are dangerous?
Answer from a Biosafety Officer:
June 10, 2013
The most straightforward answer to your question is that you can’t tell whether a culture of bacteria is "safe" or "dangerous" just by looking at the appearance of colonies on a plate. Colony morphology (the shape, color, and general appearance of a bacterial colony on a plate) is one aspect of bacterial identification and can be used as a step in identifying the cultures on your plate (1).
For this reason, biosafety guidelines recommend using Biosafety Level 2 (BSL-2) practices and facilities when working with samples that contain unknown microbes, and therefore unknown hazards (2: Section II: Biological Risk Assessment; 3: Isolation of Unknown Microbes from the Environment).
1. Breakwell, D., Woolverton, C., MacDonald, B., Smith, K., and R. Robison. Colony Morphology. ASM MicrobeLibrary. http://www.microbelibrary.org/component/resource/laboratory-test/3136-colony-morphology-protocol. Accessed 03/01/2013.
2. Wilson, D., and L. Chosewood, editors. Biosafety in Microbiological and Biomedical Laboratories (BMBL), 5th edition. Centers for Disease Control and Prevention and National Institutes of Health. 2009. http://www.cdc.gov/biosafety/publications/bmbl5/. Accessed 03/03/2013.
3. American Society for Microbiology. Draft Guidelines for Biosafety in Teaching Laboratories. 2012. http://www.asmcue.org/documents/ASMBiosafetyGuidelines-v2.pdf. Accessed 03/03/2013.