I have an unknown culture that began as a yellow broth on Day 1. However, 18 hours later, after incubation, the broth turned pink. Any idea of what organism(s) this could be?
To identify the organism responsible for the color change in your culture, you will need to consider a few factors. Here is a step-by-step method to help you narrow down the possibilities:
1. Start by observing the broth's physical characteristics: Take note of its appearance, growth pattern (e.g., suspended cells, pellicle formation), and any distinct odor. These details can provide clues about the organism.
2. Next, analyze the color change: In this case, the yellow broth turning pink suggests a pH indicator might be involved. Some organisms produce acidic or alkaline byproducts during growth, which can cause a color change in the medium if a pH indicator is present. Note that not all bacteria produce visible pigment.
3. Determine the pH indicator used: pH indicators are commonly added to differentiate between species or genera of bacteria. The typical pH indicators employed are phenol red (changes from yellow to pink below pH 6.8) or bromothymol blue (changes from yellow to green below pH 6.0). Identifying the specific pH indicator will assist in narrowing down the potential organisms.
4. Research the expected reactions: Once you know the pH indicator used, consult reliable sources (e.g., scientific literature, databases) to find information on which organisms typically cause a color change with that indicator. Some bacteria, such as Escherichia coli or certain strains of Enterobacter, can ferment sugars and produce acids, leading to a pH decrease and color change from yellow to pink.
5. Perform further tests: If the initial observations and research narrowed down the possibilities but you need a definitive identification, additional tests such as biochemical tests or molecular techniques (e.g., PCR, DNA sequencing) can help confirm the organism's identity.
Remember that without more specific information or test results, it's challenging to pinpoint the exact organism responsible for the color change. However, going through these steps will assist you in making educated hypotheses and guiding further investigations.