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This results in a change of the medium's color from green (neutral) to blue (alkaline). Bacterial colonies are picked up from a straight wire and inoculated into slope of Simmons citrate agar and incubated overnight at 37 °C. Inoculating from a broth culture is not recommended because the inoculum would be too heavy.
The genus Klebsiella was named after the German microbiologist Edwin Klebs (1834–1913). [citation needed] It is also known as Friedlander's bacillum in honor of Carl Friedländer, a German pathologist, who proposed that this bacterium was the etiological factor for the pneumonia seen especially in immunocompromised individuals such as people with chronic diseases or alcoholics.
The agar contains citrate and ammonium ions (nitrogen source) and bromothymol blue (BTB) as a pH indicator. [2] Bromothymol blue was added in order to reduce false positives. The citrate agar is green before inoculation, and turns blue, because of BTB as a positive test indicator, meaning citrate is utilized.
Klebsiella aerogenes, [2] previously known as Enterobacter aerogenes, is a Gram-negative, oxidase-negative, catalase-positive, citrate-positive, indole-negative, rod-shaped bacterium. [3] Capable of motility via peritrichous flagella, [ 4 ] it is approximately one to three microns in length.
On carbohydrate-rich media, Klebsiella colonies appear greyish-white in colour with a mucosal outer surface. [6] The media used for selecting for Klebsiella species in a mixed sample is an agar including ornithine, raffinose, and Koser citrate, where members of this genus will form yellow, wet-looking colonies. [8]
Simmons’ citrate agar was developed by James S. Simmons in 1926 by adding 1.5% agar and bromothymol blue as a pH indicator to Koser’s citrate agar to observe changes in pH as a result of oxidative reactions from citrate metabolism. [5]
Klebsiella oxytoca on agar plate. Klebsiella oxytoca is a Gram-negative, rod-shaped bacterium that is closely related to K. pneumoniae, from which it is distinguished by being indole-positive; it also has slightly different growth characteristics in that it is able to grow on melezitose, but not 3-hydroxybutyrate.
Mueller–Hinton agar is frequently used in the disc diffusion test. [14] The Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) provide standards for the type and depth of agar, temperature of incubation, and method of analysing results. [11]