Which of the following microbes is gram-positive and an anaerobe?

Clostridium perfringens is recognized as a gram-positive anaerobic bacterium. In the Gram staining procedure, it retains the crystal violet dye, leading to a purple appearance, which characterizes gram-positive bacteria. Additionally, Clostridium perfringens thrives in anaerobic environments, meaning it can grow and reproduce without the presence of oxygen. This bacterium is known for being part of the normal flora in the intestines but can also cause food poisoning and serious infections, particularly in wounds.

In contrast, the other microbes listed do not fit the criteria of being both gram-positive and anaerobic. Legionella pneumophila is a gram-negative bacterium that causes pneumonia and requires oxygen for growth. Escherichia coli is also gram-negative and typically facultative anaerobic, meaning it can survive in both aerobic and anaerobic environments but is not exclusively anaerobic. Staphylococcus aureus, while gram-positive, is typically aerobic or facultatively anaerobic, and therefore does not meet the requirement of being strictly anaerobic.