Typical Gram stainsTypical Gram stainsClusters: 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,
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.
