Identification of Gram‐Positive Bacteria

Abstract

Unlike in the case of Gram‐negative bacilli, it can be difficult to definitively identify Gram‐positive cocci and bacilli to the genus and species levels. Gram‐positive bacilli have been difficult to identify because pathogens have to be discerned from hundreds of validly named species that are found in the environment or are part of the normal microbiota of the human body, including the skin, mucosal membranes, oropharynx, and genitourinary and gastrointestinal tracts, and the taxonomy of such agents is both evolving and being augmented. For species‐level identification of viridans group streptococci, enterococci, and corynebacteria, commercial kits are often easier to perform than standard tube biochemical tests, but both approaches have limitations in accuracy. Because of the lack of unique colony morphologies for many Gram‐positive microorganisms, the Gram stain must be performed on isolates for identification. Gram‐variable microorganisms are considered Gram positive.