Routella ornithinolytica colony morphology on CLED agar

Raoultella ornithinolytica, previously classified under the genus Klebsiella, is a Gram-negative, encapsulated, non-motile, rod-shaped bacterium. It is known to inhabit various environments, including water, soil, and as part of the flora in the gastrointestinal tracts of humans and other mammals. R. ornithinolytica is an opportunistic pathogen that can cause infections in humans, particularly in individuals with compromised immune systems. On CLED (Cystine Lactose Electrolyte Deficient) agar, which is commonly used for the isolation and differentiation of urinary tract pathogens, the colony morphology of R. ornithinolytica can exhibit specific characteristics:
Colony Color and Appearance: R. ornithinolytica, being a lactose fermenter, typically produces colonies that are yellow or yellowish in color on CLED agar. This yellow coloration results from the acid production through lactose fermentation, which changes the pH and causes the pH indicator in the agar to shift to yellow.
Colony Size: The colonies of R. ornithinolytica can vary in size but are generally medium to large after 24 hours of incubation at 37°C.
Colony Texture: The colonies are usually smooth, rounded, and exhibit a mucoid texture due to the production of a polysaccharide capsule, which is a common feature among members of the former Klebsiella genus.
Edge: Colonies typically have a well-defined edge, making them easily distinguishable under a colony counter or when examining the agar plate directly.
It's important to note that while CLED agar provides a good medium for distinguishing lactose fermenters through colony color, the identification of R. ornithinolytica should be confirmed with additional biochemical tests and molecular methods. This is due to the close relatedness and overlapping characteristics with other species within its family, such as Klebsiella spp., which may also present similarly on CLED agar. Identification techniques may include tests for ornithine decarboxylase activity (a characteristic feature of R. ornithinolytica), urease production, and molecular methods such as PCR for species-specific genes.
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