Which type of bacteria does not require oxygen to survive?

Anaerobic bacteria are the correct answer because they thrive in environments devoid of oxygen. These bacteria have adapted to survive and reproduce in conditions where oxygen is absent or present in very low levels. Unlike aerobic bacteria, which require oxygen to grow and function, anaerobic bacteria utilize different metabolic pathways for energy production that do not involve oxygen. This allows them to inhabit various environments, including within the human body, such as in the gastrointestinal tract, where oxygen levels are minimal.

In contrast, aerobic bacteria depend on oxygen for their energy needs, highlighting that not all bacteria can exist without oxygen. Pathogenic bacteria can be either aerobic or anaerobic—this category includes any bacteria that cause disease, lacking specificity concerning oxygen requirements. Microaerophilic bacteria require reduced levels of oxygen but not a complete absence. This specific need differentiates them from strictly anaerobic bacteria, further emphasizing why anaerobic bacteria is the most appropriate choice in context.