Which type of micro-organism does not require free oxygen?

Anaerobes are types of micro-organisms that do not require free oxygen for growth and can even be harmed or killed by its presence. These organisms thrive in environments where oxygen is limited or absent, such as deep tissues, muddy waters, and the intestines of animals. This characteristic differentiates them from aerobes, which need oxygen to survive and reproduce.

Understanding the environment in which different micro-organisms thrive is crucial in microbiology, especially in clinical settings, as it impacts choices regarding treatment and control measures for infections. Other choices like aerobe pertain to organisms relying on oxygen, while pathogen refers broadly to disease-causing organisms, and bactericide signifies substances that kill bacteria rather than describing a specific type of microorganism. Therefore, anaerobes' distinct relationship with oxygen is key to their survival and categorization.