The δ-ALA test is confirmatory for the identification of which requirement in Haemophilus species?

The δ-ALA test is specifically designed to confirm the requirement for the X factor (also known as hemin or hemoglobin) in Haemophilus species. Haemophilus species are fastidious, meaning they require certain nutrients to grow in culture. The X factor is essential for their growth, and its requirement can be determined through biochemical testing.

In the δ-ALA test, the organism's ability to synthesize porphyrins and subsequently, hemin, is evaluated. If the organism can produce porphyrins, it will not need to rely on an external source of X factor for growth, indicating it does not have this requirement. Conversely, if the organism cannot synthesize porphyrins, it will require X factor from an external source for growth.

Understanding the role of X factor is crucial in distinguishing between different species of Haemophilus, as some species require both X factor and V factor (which is nicotinamide adenine dinucleotide, NAD) for growth, while others may need only one. This test is an important aspect of microbiological identification in the clinical setting.