Which organism is an example of obligate anaerobes?

Which organism is an example of obligate anaerobes?

• A. Pseudomonas
• B. Clostridium
• C. Escherichia coli
• D. Staphylococcus aureus

Answer: (B)

Obligate anaerobes cannot survive in the presence of oxygen and must grow in environments without it. Their metabolism and lack of protective enzymes make oxygen harmful to them. Clostridium fits this pattern precisely: it is a Gram-positive, spore-forming rod that thrives in anaerobic conditions such as deep soil or oxygen-free wounds. This group includes notable pathogens like C. difficile, C. tetani, and C. botulinum, illustrating the strict need for an absence of oxygen. In contrast, Pseudomonas species require oxygen to grow and are considered obligate aerobes. Escherichia coli and Staphylococcus aureus are capable of growing with or without oxygen (facultative anaerobes), using aerobic respiration when oxygen is available and switching to fermentation or anaerobic respiration otherwise.

Obligate anaerobes cannot survive in the presence of oxygen and must grow in environments without it. Their metabolism and lack of protective enzymes make oxygen harmful to them. Clostridium fits this pattern precisely: it is a Gram-positive, spore-forming rod that thrives in anaerobic conditions such as deep soil or oxygen-free wounds. This group includes notable pathogens like C. difficile, C. tetani, and C. botulinum, illustrating the strict need for an absence of oxygen.

In contrast, Pseudomonas species require oxygen to grow and are considered obligate aerobes. Escherichia coli and Staphylococcus aureus are capable of growing with or without oxygen (facultative anaerobes), using aerobic respiration when oxygen is available and switching to fermentation or anaerobic respiration otherwise.