True cocci, such as most Neisseria spp.and Moraxella (Branhamella) catarrhalis, can be differentiated from morphologically similar Moraxella species by

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The Moraxella discussed in this chapter are either coccobacilli or short to medium-sized, gram-negative rods. Subinhibitory concentrations of penicillin, such as occurs in the presence of a 10-unit penicillin disk, cause the coccoid forms of these bacteria to elongate to a bacillus morphology. In contrast, True cocci, such as most Neisseria spp. and Moraxella (Branhamella) catarrhalis, with which these organisms may be confused, maintain their original coccus shape in the presence of penicillin.

True Cocci, Such as Most Neisseria Spp