What it means
One of the two main groups of bacteria sorted by the Gram staingram staynA lab staining method that sorts bacteria into two groups by the color they turn under the microscope.Full entry . Gram-negative bacteria have a thin cell wall covered by an outer membrane, so they do not hold the purple dye and look pink or red under the microscope. The outer membrane contains endotoxin and helps them resist many antibiotics. Examples are E. coli, Klebsiella, Pseudomonas and Neisseria. The name comes from Hans Christian Gram, the Danish scientist who created the stain.
At a glance
| Also written | gram negative |
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Easy to confuse with
gram-positive
Describes bacteria that stain purple with the Gram stain because of their thick cell wall.
Related terms
gram-positive
Describes bacteria that stain purple with the Gram stain because of their thick cell wall.
Gram stain
A lab staining method that sorts bacteria into two groups by the color they turn under the microscope.