Download Differences between Gram+ and Gram

Differences between Gram+ and Gram- bacteria
1. Gram+ have a thick peptidoglycan layer. Gramhave a thin layer.
2. Gram- have a second lipid membrane outside
the plasma membrane, with an intermembrane
space (periplasm). The outer membrane is part
of the outer lipid envelope, which contains LPS
(lipopolysaccharide). LPS causes fever. Gram+
do not have these structures.
Explanation of Gram staining properties
1. Gram+: Alcohol causes shrinkage of the pores
in the peptidoglycan layer. Dye is trappped
within the pores.
2. Gram-: Dye initially binds within the outer lipid
envelope. But the alcohol dissolves this
structure, so the dye washes away
Mycobacteria
• Cause tuberculosis (M. tuberculosis); leprosy (M.
leprae); and AIDS-related pneumonia (M. avium)
• Have properties of both Gram+ and Gram- bacteria:
Have a thick peptidoglycan, but also have an outer
membrane. However, the outer membrane is
structurally different from that of typical Gram- bacteria
• Have a waxy coat containing mycolic acid (a lipid) which
prevents penetration of many dyes. But this is stained
by the acid-fast dye, which will not wash away.
• Therefore, do not stain Gram+, despite the thick
peptidoglycan.