Raoultella

Raoultella planticola Standard I colonies 97

Raoultella planticola MacConkey colonies 32

Raoultella is a genus of Gram-negative bacteria, belonging to the family Enterobacteriaceae. The genus was named after the French microbiologist Didier Raoult. Initially classified within the genus Klebsiella as a part of the Klebsiella planticola and Klebsiella trevisanii complexes, Raoultella was later distinguished as a separate genus based on differences in DNA-DNA hybridization, 16S rRNA gene sequencing, and certain biochemical characteristics.

Characteristics

Raoultella species are non-motile, encapsulated, and rod-shaped bacteria that are commonly found in the environment, including water, soil, and plants. They are also present in the gastrointestinal tracts of humans and animals, indicating their role in the natural flora. These bacteria are capable of reducing nitrate to nitrite and are known for their ability to produce gas from lactose fermentation. One of the distinguishing biochemical features of Raoultella is its ability to produce ornithine decarboxylase, an enzyme not produced by members of the closely related genus Klebsiella.

Pathogenicity

While Raoultella species are primarily environmental and not typically associated with disease, there have been increasing reports of these bacteria causing infections in humans. These infections can range from urinary tract infections, pneumonia, cholangitis, and soft tissue infections to more severe cases like septicemia. Raoultella planticola, in particular, has been identified as an emerging opportunistic pathogen. The risk of infection is higher in individuals with compromised immune systems, underlying health conditions, or those undergoing invasive procedures. The treatment of Raoultella infections involves the use of antibiotics, although resistance to commonly used antibiotics has been observed, complicating treatment efforts.

Species

The genus Raoultella consists of several species, including:

• Raoultella planticola
• Raoultella ornithinolytica
• Raoultella terrigena
• Raoultella electrica

Genomics and Identification

The identification of Raoultella species in clinical and environmental samples is primarily based on biochemical tests, although molecular methods such as 16S rRNA gene sequencing have become increasingly important for accurate identification. The genomics of Raoultella species have been explored to understand their evolutionary relationships, antibiotic resistance mechanisms, and potential virulence factors.

Ecology

Raoultella species play a role in the nitrogen cycle through their ability to reduce nitrate to nitrite. They are commonly found in aquatic environments, soil, and on plants, where they can contribute to the decomposition of organic material. Their presence in the gastrointestinal tracts of animals suggests a role in the gut microbiome, although the specific functions and interactions with other gut microbes are not well understood.

Clinical Significance

The emergence of Raoultella as a cause of opportunistic infections in humans has led to increased interest in understanding the pathogenic mechanisms, antibiotic resistance patterns, and strategies for effective treatment. The ability of these bacteria to acquire and transfer antibiotic resistance genes makes them a potential public health concern.