A sheep blood agar plate is used as a primary isolation medium for all the following organisms except:

Sheep blood agar is a rich medium that provides nutrients for the growth of a wide variety of bacteria, particularly those that require enriched conditions to thrive. It is particularly useful for isolating and identifying hemolytic bacteria, especially streptococci and staphylococci, due to the presence of red blood cells, which allow for hemolysis.

Haemophilus influenzae and Haemophilus parainfluenzae, while they can grow on sheep blood agar, typically require additional growth factors that are not supplied in sufficient quantities by this medium alone. These organisms are often best isolated using chocolate agar, which provides lysed red blood cells and the necessary factors such as hemin (X factor) and nicotinamide adenine dinucleotide (V factor), allowing them to grow more effectively.

In contrast, the other organisms mentioned are either suitable for growth on sheep blood agar or can produce hemolytic reactions, making the medium appropriate for their isolation. Hemolytic streptococci and coagulase-positive staphylococci are commonly isolated on this agar due to their hemolytic activity, while Proteus spp. and Escherichia coli, as well as Pseudomonas spp. and Acinet