Colonial morphology

When a specimen arrives in the microbiology laboratory, it is inoculated into an agar plate and placed in an incubator to encourage microbial growth.

[2]: 518  The microbiologist examines the appearance of the colony, noting specific features such as size, colour, shape, consistency, and opacity.

Staphylococci are considered to have a creamy consistency,[1]: 173  while some Neisseria species are sticky, and colonies of diphtheroid bacteria and beta-hemolytic streptococci are typically dry.

[2]: 500  Clostridium perfringens, which causes gas gangrene, is noteworthy for producing a "double zone" of both complete and incomplete hemolysis.

Pseudomonas aeruginosa produces the pigments pyocyanin and pyoverdin, which give the colonies a greenish sheen.

[5]: 26 [8]: 236  Organisms with swarming motility, like Proteus species, exhibit concentric waves of growth extending from the inoculation point.

[10] Based on the visual appearance of the colonies, microbiologists can narrow down the list of possible organisms, allowing them to select appropriate tests to provide a definitive diagnosis.

[1]: 309–14 Although automated techniques like MALDI-TOF are increasingly used to identify microorganisms in clinical laboratories, colonial morphology remains useful to distinguish potential pathogens, which must be identified, from normal flora, for which definitive identification is unnecessary,[1]: 163  and to confirm identification when automated techniques give inconclusive results.