Lactobacillus delbrueckii subsp. Bulgaricus is a species of gram positive bacteria in the genus Lactobacillus. A specially selected strain of Lactobacillus bulgaricusis available as a culture concentrate or as part of a multiple strain custom blend with a variety of excipients. It is a gram-positive rod that may appear long and filamentous. It is non-motile and does not form spores. It is regarded as aciduric or acidophilic, since it requires a low pH (around 5.4–4.6) to grow effectively. It is available as white to cream-colored, free-flowing powder.