What type of bacterium is Escherichia coli?

Escherichia coli is classified as a Gram-negative, facultative anaerobic bacillus. This means that it appears pink when subjected to Gram staining, a process that differentiates bacteria based on their cell wall composition. The Gram-negative designation indicates that E. coli has a thin peptidoglycan layer surrounded by an outer membrane, which is characteristic of many pathogenic and non-pathogenic bacteria.

As a facultative anaerobe, E. coli has the ability to grow in both the presence and absence of oxygen. This adaptability allows it to thrive in various environments, including diverse conditions in the human gut and other habitats. The bacillus classification means that E. coli has a rod-like shape, which is typical for this genus.

Other choices do not accurately represent the classification of E. coli. For instance, a Gram-positive bacterium would have a thicker peptidoglycan layer and would stain purple in a Gram stain, which is not the case for E. coli. Additionally, being an obligate anaerobe or strictly aerobic contradicts E. coli’s facultative nature, as it can utilize oxygen when available but does not require it for survival.