What type of bacteria does the term "coliform" refer to?

The term "coliform" refers specifically to a group of Gram-negative, rod-shaped bacteria that are commonly found in the environment, as well as in the intestines of warm-blooded animals. These bacteria are a significant indicator of water quality because their presence suggests that water may be contaminated with fecal material. Coliforms include both non-pathogenic and pathogenic species, but they are primarily understood in the context of monitoring sanitation in water.

This classification as Gram-negative rod-shaped bacteria is crucial because it highlights their cellular structure, which is characterized by a thin peptidoglycan layer and an outer membrane containing lipopolysaccharides. This unique structure affects how these bacteria react to different stains and antibiotics, which is vital information in microbiology and water testing.

The alternatives present other types of bacteria that do not fit the definition of coliforms. Gram-positive cocci refer to a different group characterized by thick peptidoglycan layers in their cell walls, spore-forming bacteria are known for their ability to survive in harsh conditions through spore formation, and pathogenic bacteria only speaks to those capable of causing disease, which does not encompass the broader range of bacteria included in coliform classification.