Typical Gram stains


Gram-positive bacteria

Gram-positive cocci

Clusters: usually characteristic of Staphylococcus spp., such as S. aureus

 

Chain: usually characteristic of Streptococcus spp., such as S. pneumoniae, B group streptococci

 

Tetrad: usually characteristic of Micrococcus spp.

 

Gram positive bacilli

Thick : usually characteristic of Clostridium spp., such as C. perfringens, C. septicum,

C. tetanomorphum

 

Thin: usually characteristic of Listeria spp.

 

Branched: usually characteristic of Actinomycetes and Nocardia , such as A. israelii Note: Mycobacteria are not branched, and often stain poorly with Gram stain. Some mycobacteria do appear as Gram-positive rods, not unlike diptheroids, sometimes with Gram-positive beading.

Gram negative bacteria


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