What is the likely identification of a small, gram-negative coccobacillus that is indole positive and requires X factor for growth?

The identification of a small, gram-negative coccobacillus that is indole positive and requires X factor for growth is indicative of Haemophilus influenzae. This organism belongs to the Haemophilus genus, which is characterized by its requirement for specific growth factors, particularly X factor (heme).

H. influenzae is well-known for being part of the normal flora of the upper respiratory tract but can also be an opportunistic pathogen, causing a range of infections from respiratory diseases to meningitis. The indole positivity is a crucial biochemical characteristic, as H. influenzae is one of the strains that can metabolize tryptophan to produce indole, setting it apart from other Haemophilus species that do not share this trait.

In contrast to other members of the Haemophilus genus mentioned in the options, H. parainfluenzae and H. aphrophilus are usually indole negative, while H. ducreyi, associated with chancroid, typically does not show indole positivity under standard testing conditions. This biochemical profile is critical for accurate identification in laboratory settings and significantly aids in diagnosing the infections caused by these organisms.