Bacteria that can survive without the presence of oxygen are called anaerobic bacteria. They are able to generate energy through processes other than aerobic respiration, such as fermentation or anaerobic respiration. Some examples of anaerobic bacteria include:

- Clostridium botulinum: This bacterium produces the neurotoxin that causes botulism, a serious form of food poisoning. It is found in soil and can contaminate food products such as canned goods.

- Escherichia coli (E. coli): Some strains of E. coli are anaerobic and can cause infections such as urinary tract infections and food poisoning.

- Bacteroides fragilis: This bacterium is part of the normal gut flora but can cause infections if it enters other parts of the body, such as the bloodstream or abdominal cavity.

- Methanogens: These bacteria produce methane as a byproduct of their metabolism and are found in environments such as swamps, marshes, and landfills.