Citrobacter is a genus of gram-negative bacteria, members of Enterbacteriaceae family. There are 11 genotypically and biochemically diverse Citrobacter species that are commonly found in water, sewage, soil, and foods. Citrobacter species are also part of normal and pathogenic microbial flora of a number of animals, including cold-blooded vertebrates, humans, dogs, cats, horses, cows, birds, and tortoises. They are also considered to be important pathogens in fish (trout, bass, channel catfish, and tropical aquarium fish). C. rodentium causes bowel disease in laboratory mice and bloody diarrhea in gerbils.2

Citrobacter abscessA painful abscess caused by Citrobacter species
Source: PubMed Central

Human Pathogens

In humans Citrobacter species have been linked to relatively infrequent cause of bacterial infections in hospitalized patients including surgical wound infections, cellulitis, as well as urinary tract and blood infections. Most patients who develop these infections have underlying risk factors such as prolonged hospital stays, immunosuppression, malignancies, liver and gallbladder disease, and invasive devices.3 The most common and most antibiotic-resistant species isolated from clinical samples is C. freundii.4,5 Citrobacter species are often present in bacterial cultures from persons with "swimmer's ear", the most common ear inflammatory disease faced by swimmers.1

Newborn babies are at increased risk of infection, typically from C. koseri (formerly C. diversus), C. freundii, and C. sedlakii. These organisms tend to cause sepsis and inflammation of the brain ventricles with frequent multiple brain abscesses. They have a unique ability to penetrate, survive, and replicate in the cells of blood vessel and macrophages.6

Food Contaminants

Citrobacter species have been recovered from farm products such as vegetables, dairy products, and shellfish. C. freundii produces a toxin identical to the heat-stable toxin of enterotoxigenic E. coli (ETEC). This toxin interferes with water and electrolyte absorbing mechanism in the intestines which results in severe diarrheal disease with vomiting, fever, and pain. The symptoms may develop within 12-24 hours of consuming contaminated food.7


  1. David Schlossberg. Infections of Leisure
  2. J. Michael Janda, Sharon L. Abbott. The Enterobacteria
  3. Robert C. Owens, Ebbing Lautenbach. Antimicrobial resistance: problem pathogens and clinical countermeasures
  4. Mark Shirtliff, Jeff G. Leid. The Role of Biofilms in Device-Related Infections
  5. Paul G. Engelkirk, Janet L. Duben-Engelkirk. Laboratory diagnosis of infectious diseases: essentials of diagnostic microbiology
  6. Paul S. Babyn. Teaching atlas of pediatric imaging
  7. Morton Satin. Food alert!: the ultimate sourcebook for food safety



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