differences between gram+ and gram- bacteria 1.gram+ have a thick peptidoglycan layer. gram- have a...
TRANSCRIPT
Differences between Gram+ and Gram- bacteria
1. Gram+ have a thick peptidoglycan layer. Gram- have 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.