Which type of bacteria is known for growing in chains?

Streptococcus is the type of bacteria known for growing in chains. This genus is composed of spherical-shaped bacteria (cocci) that divide in one plane, resulting in the characteristic chain formation. The arrangement is due to their mode of reproduction through binary fission, where the cells adhere to one another after they split, leading to the appearance of long chains.

In contrast, the term "cocci" refers more generally to spherical bacteria and does not specify their arrangement, meaning they can exist alone, in pairs (diplococci), in clusters (staphylococci), or in chains (streptococci). Bacillus refers to rod-shaped bacteria, and while they may also form chains under certain conditions, their distinguishing characteristic is their elongated shape rather than a chain arrangement. Spirilla, on the other hand, are spiral-shaped bacteria and do not form chains either. Therefore, Streptococcus is distinctly recognized for its chaining formation, making it the correct choice.