Final answer:
The group of bacteria that forms clusters is Staphylococcus, which are known for their grape-like arrangement and include species like S. epidermidis and S. aureus.
Step-by-step explanation:
The group of bacteria that forms clusters is Staphylococcus. These bacteria are characterized by their grape-like cluster appearance when viewed under a microscope. Staphylococcus spp. are facultative anaerobes, which means they can tolerate the presence of oxygen but can also live without it. Two well-known species of this genus are S. epidermidis and S. aureus, both of which are common on human skin and can be opportunistic pathogens. It's important to not confuse Staphylococcus with Streptococcus, which typically form chains, or Clostridium, which are obligate anaerobes and form endospores, or other genera such as Corynebacterium and Lactobacillus that do not form clusters.