Raoultella ornithinolytica-Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes

Raoultella ornithinolytica-Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes


Raoultella ornithinolytica, a Gram-negative, encapsulated, non-motile, rod-shaped bacterium, belongs to the Enterobacteriaceae family. Initially, researchers classified it under the genus Klebsiella, but later reclassified it due to its significant genetic and biochemical differences. Various environments, including water, soil, and the gastrointestinal tracts of humans and other mammals, harbor this organism. Its unique ability to degrade ornithine through the enzyme ornithine decarboxylase sets it apart from closely related species.

As an opportunistic pathogen, Raoultella ornithinolytica can inflict a range of infections on individuals, especially those with compromised immune systems. Capsular polysaccharides and siderophores serve as its virulence factors, enhancing its resistance to host immune responses and enabling it to acquire essential nutrients, respectively. Its infections, although relatively rare, can be severe and include urinary tract infections, pneumonia, bacteremia, and wound infections.

The bacterium’s resistance to multiple antibiotics complicates treatment, underscoring the need for precise identification and susceptibility testing in clinical microbiology. Current research aims to delve into its pathogenic mechanisms, patterns of antibiotic resistance, and possible biotechnological applications, given its distinctive metabolic properties.



  1. Its Gram-negative, rod-shaped form increases virulence.
  2. Lacking flagella distinguishes it from some Enterobacteriaceae.
  3. It ferments lactose, producing acid and gas.
  4. The enzyme ornithine decarboxylase decarboxylates ornithine.
  5. Under microscopes, it shows as short rods.
  6. It forms pink to red colonies on MacConkey agar.
  7. A mucoid appearance indicates its polysaccharide capsule.
  8. Acid production from lactose helps identify it.
  9. Microbiologists must understand its morphology for identification.
  10. Its unique properties attract research interest.


Raoultella ornithinolytica, a Gram-negative, encapsulated, rod-shaped bacterium in the Enterobacteriaceae family, has a morphology that significantly contributes to its pathogenicity. Its encapsulation crucially boosts its virulence by protecting against phagocytosis and aiding the bacterium’s survival and proliferation within the host. This organism stands out for its ability to ferment lactose, produce gas, and uniquely decarboxylate ornithine to putrescine using the ornithine decarboxylase enzyme, setting it apart from similar species.

Various virulence factors, including siderophores that R. ornithinolytica produces, play a notable role in its pathogenic potential by allowing iron acquisition from the host, thus enhancing bacterial growth and virulence. Moreover, the bacterium’s resistance to many antibiotics presents a challenge to treatment protocols, highlighting the need to grasp its pathogenic mechanisms fully.

Despite their relative rarity, infections by R. ornithinolytica can be severe and cover a wide spectrum, including urinary tract infections, pneumonia, bacteremia, and wound infections. Its capacity to flourish in diverse environments like water and soil, along with its presence in the gastrointestinal tracts of humans and other mammals, aids its transmission and elevates the risk of opportunistic infections, particularly for people with compromised immune systems.

Lab Diagnosis

The laboratory diagnosis of Raoultella ornithinolytica infections involves a combination of culture techniques, biochemical tests, and molecular methods to accurately identify the organism and guide appropriate treatment. Initially, specimens from the suspected infection site (e.g., urine, blood, or wound swabs) are cultured on selective media such as MacConkey agar, which supports the growth of Gram-negative bacteria. On this medium, R. ornithinolytica typically produces pink or red colonies due to lactose fermentation, a characteristic shared with other coliform bacteria.

Further differentiation and identification rely on biochemical testing. R. ornithinolytica is positive for ornithine decarboxylase activity, a distinctive feature that differentiates it from many related species. This bacterium is also capable of producing gas from glucose and is usually urease positive. The utilization of specific substrates and resistance to certain antibiotics can further assist in identification, although it’s important to note that R. ornithinolytica has shown increasing resistance to multiple antibiotics, complicating treatment.

For more definitive identification, molecular diagnostic methods, such as polymerase chain reaction (PCR), can be employed to detect species-specific DNA sequences. These molecular techniques offer high specificity and sensitivity, crucial for distinguishing R. ornithinolytica from closely related organisms.

Antimicrobial susceptibility testing is essential following identification, given the organism’s potential for antibiotic resistance. This testing helps in selecting the most effective antimicrobial therapy for treating infections caused by R. ornithinolytica.


Doctors typically treat Raoultella ornithinolytica infections with antibiotics. They choose antibiotics based on susceptibility tests. Carbapenems effectively combat many strains. Specific resistance patterns guide antibiotic choice. Doctors often use broad-spectrum antibiotics initially. Combination therapy may help in severe cases or with immunocompromised patients. Supportive care is crucial for managing symptoms. Early pathogen identification leads to targeted treatment. Monitoring R. ornithinolytica’s resistance is vital for treatment strategies.


Preventing infections caused by Raoultella ornithinolytica, an opportunistic pathogen found in environments such as water and soil, and occasionally in food, requires a multifaceted approach. Key strategies include maintaining strict hygiene practices in healthcare settings, particularly during invasive procedures or for patients with indwelling devices, to minimize the risk of nosocomial infections. In the community, proper food handling and preparation techniques can reduce foodborne transmission, especially for foods that are consumed raw or minimally processed.

Water treatment and sanitation are crucial to control the bacterium’s presence in water supplies and prevent its spread. Hand hygiene, both in healthcare facilities and among the general population, remains a cornerstone of preventing the spread of infections, including those caused by R. ornithinolytica. For individuals with weakened immune systems, extra precautions may be necessary, including avoiding the consumption of potentially contaminated food and water.

Awareness and education about the risks and routes of transmission of R. ornithinolytica can further aid in prevention efforts. Regular monitoring and reporting of infection outbreaks also play a vital role in early detection and containment. By implementing these preventive measures, the incidence of R. ornithinolytica infections can be significantly reduced, protecting public health and reducing the burden on healthcare systems.


Raoultella ornithinolytica belongs to Enterobacteriaceae.

  • Its encapsulation enhances virulence.
  • The bacterium ferments lactose.
  • It uniquely decarboxylates ornithine.
  • Siderophores boost its pathogenicity.
  • Antibiotic resistance complicates treatment.
  • Infections can be severe.
  • It thrives in diverse environments.
  • Transmission risk increases in immunocompromised individuals.

Further Readings

  • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7167274/
  • https://bmcinfectdis.biomedcentral.com/articles/10.1186/s12879-021-06799-w
  • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3101735/
  • https://www.sciencedirect.com/science/article/pii/S1201971216000345
  • https://www.frontiersin.org/articles/10.3389/fped.2020.00362/full
  • https://www.onehealthjournal.org/Vol.7/No.1/1.pdf
  • https://www.onehealthjournal.org/Vol.7/No.1/1.pdf
  • https://www.bjid.org.br/en-raoultella-ornithinolytica-causing-fatal-sepsis-articulo-S141386701500032X
  • https://www.sciencedirect.com/science/article/abs/pii/S1341321X23000351
  • https://www.scielo.br/j/bjid/a/nsSsyK7Nhyf7Zf3WkCYckdx/
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