The outcome of this pH indicator assessment distinguishes between bacteria capable of mixed acid fermentation and those that are not. A positive outcome is visualized as a red coloration of the culture medium, indicating a pH below 4.4 due to the production of stable acidic end-products. Conversely, a negative outcome manifests as a yellow color, signifying a pH above 6.2. Occasionally, an orange color might be observed, suggesting a pH between these values, representing an inconclusive result.
This simple colorimetric assay plays a crucial role in bacterial identification and differentiation, particularly within the family Enterobacteriaceae. Its development, along with other similar tests, provided a relatively quick and inexpensive method for classifying microorganisms based on their metabolic pathways, significantly advancing microbiological analyses in various fields like diagnostics, food safety, and environmental monitoring. Historically, it has been an indispensable tool in public health laboratories and remains relevant today.
