Which type of bacteria is rod-shaped?

Bacilli are a type of bacteria characterized by their rod-shaped structure. This long and cylindrical form allows for various arrangements, often seen in chains or clusters, depending on how they divide and grow. Bacilli can be further classified into specific groups based on their shape, size, and the presence or absence of flagella, which affects their movement.

In contrast, cocci are spherical bacteria that can form in various arrangements, such as clusters or chains, but they do not exhibit the elongated structure characteristic of bacilli. Spirilla are helical or spiral-shaped bacteria, while vibrio are shaped like a comma. Each type features distinct structural differences that influence their behavior, reproduction, and the diseases they may cause, but in this case, the defining feature of bacilli is their rod-like shape, confirming that the answer is indeed correct.