What type of microorganism is classified as gram negative?

Bacilli are classified as gram-negative microorganisms when they possess a thin peptidoglycan layer surrounded by an outer membrane containing lipopolysaccharides. The gram stain process reveals this classification, where gram-negative bacteria do not retain the crystal violet stain but take up the counterstain, appearing pink under a microscope.

While cocci can also be gram-negative, they are single-celled spherical bacteria that can exist in various forms and may not always be classified as gram negative. Yeast, which belongs to the fungi kingdom, is eukaryotic and does not fit within the classification of bacteria; it does not typically undergo the gram staining process. Fungi also represent a separate kingdom that encompasses organisms like molds and mushrooms, which are distinct from the bacteria being described in the question.

Thus, the correct classification of bacilli as gram-negative highlights important distinctions in microbiology, specifically regarding the structural differences in cell walls that impact how these microorganisms can be studied and treated.