Some
bacteria are classified as either Gram positive or Gram negative
bacteria.These method was developed by a Danish bacteriologist Hans
Christian Joachim Gram noted for his development of Gram stain.The
gram staining method is used to differentiate bacteria based on the chemical
and physical properties of their cell walls peptidoglycan enabling
it to pick up stains.
Both Gram positive and negative bacteria picks up the counter
stain however, the counter stain remain unseen on the gram positive
bacteria due to the darker crystal violet stain.
Gram positive bacteria
are those bacteria with a thick layer peptidoglycan present in
cell wall.Gram positive bacteria are able to retain the crystal violet dye
due to the presence of this thick layer of peptidoglycan and
thus stained violet or purple.
Gram negative bacteria
are
those bacteria with a thin layer peptidoglycan present in it cell wall.Gram
negative bacteria does not pick up primary stain (Crystal violet)
after discoloration with alcohol but pick up the counter
stain commonly safranin or carbol
fuchsine and are stained pink.