Typical Gram Stains

Gram-negative bacteria

Gram-negative cocci

Diplococci: usually characteristic of Neiseria spp., such as N. meningitidis

In addition, Moraxella spp. and Acinetobacter spp.are often diplococcal in morphology. Acinetobacter can be pleomorphic, and sometimes appear as Gram-positive cocci.


Coccobacilli: usually characteristic of Acinetobacter spp., which can be either Gram-positive or Gram-negative, and is often Gram-variable.


Gram-negative bacilli

Thin rods: usually characteristic of enterobacteriaceae, such as E. Coli


Coccobacilli: usually characteristic of Haemophilus spp., such as H. influenzae


Curved: usually characteristic of Vibrio spp.; Campylobactor spp., such as V. cholerae

C. jejuni


Thin needle shape: usually characteristic of Fusobacterium spp.


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