Using a sheep blood agar plate helps to eliminate which organism?

Using a sheep blood agar plate is particularly beneficial for isolating and identifying specific bacteria, particularly those that have complex growth requirements. In the context of the question, the correct answer is Haemophilus.

Haemophilus species are fastidious organisms that require specific growth factors that are present in sheep blood agar, such as hemin (factor X) and nicotinamide adenine dinucleotide (NAD, factor V). These growth factors support the growth of Haemophilus, but they are not sufficient for the growth of all bacterial species.

In contrast, the other organisms listed—Staphylococcus, Neisseria, and Streptococcus—do not have the same strict nutritional requirements and can grow in different types of media that do not contain blood. Staphylococcus, for instance, can grow on more straightforward media like mannitol salt agar, Neisseria loves chocolate agar that provides nutrients at a higher level than what is typically available, and Streptococcus can also thrive on enriched media.

Therefore, utilizing sheep blood agar helps to create an environment where Haemophilus can grow while potentially suppressing or not supporting the growth of those other organisms, making it easier to isolate and identify Haemophilus from