Proteus is a group of rod-shaped pathogenic bacteria, family Enterbacteriaceae, which cause urinary tract, infections, meningitis in newborns and infants, wound infections, rheumatoid arthritis, and gastroenteritis, but are rarely associated with foodborne illnesses.2

Proteus are Gram-negative non-sporeforming coccobacilli many of which have long, curved, filamentous forms. They are arranged in single, in pairs, or in short chains. Proteus colonies on nutrient media emit characteristic "fishy" odor. The organism has the ability to transform from a single cell form to a multi-cell elongated (swarmer) form and its colonies spread on the surface of a culture medium in successive waves (swarming pattern).3,5

Proteus species are widespread in nature, they can be found in polluted water, soil, and manure. Due to their ability to break down urea to ammonia and carbon dioxide, these organisms play an important role in decomposing organic matter of animal origin. Therefore, they are frequently isolated from animal and human feces. Proteus mirabilis is a common inhabitant of dogs, cows, pigs, and birds; Proteus vulgaris is often recovered from cows and birds.

Human Pathogen

Proteus mirabilis is part of the intestinal microbial community of humans and animals. It can also be found in decomposing meat and sewage. The organism possesses a powerful enzyme urease that breaks down urea (present in large quantities in urine) to form ammonia. This results in elevated urinary pH level and, therefore, urinary tract infections. High urinary pH can contribute directly to kidney toxicity and increased urinary stone formation. Urinary stones can result in further kidney damage by obstructing urine flow.2,4 Proteus is often the cause of bacterial invasion of the bloodstream often associated with diabetes, heart and lung disease, or cancer.4 Proteus are regarded to be an undesired element of intestinal microflora, as the bacteria may also become a causative agent of diarrhea.

While the causes of rheumatoid arthritis (RA) are not comprehensively understood, it is generally accepted that it is an autoimmune disorder which is triggered by specific microbial infections in genetically susceptible individuals, with human gut Proteus mirabilis acting as a trigger for RA. Thus, limiting the levels of gastrointestinal P. mirabilis would prevent RA initiation and minimize its downstream effects. Many antibiotics are already known to inhibit Proteus growth and/or have bactericidal effects toward Proteus species. However, the development of super-resistant bacterial strains has resulted in currently used antibiotic agents failing to end many bacterial infections. For this reason, the development of new anti-P. mirabilis chemotherapeutic agents for the prevention and treatment of RA has received recent attention. Tasmannia lanceolata (Mountain Pepper) fruit extracts were the most effective P. mirabilis growth inhibitors.6

Food Contaminant

Proteus species are commonly isolated from freshwater and saltwater fish. Contaminated fish consumption leads to a disease known as scombroid poisoning.

Animal Pathogen

Urinary tract infections caused by Proteus mirabilis are frequent in dogs and cats. In these animals, an infection with the organism can lead to formation of struvite stones in kidneys. Proteus species are occasionally involved in ear infections in dogs and cats and are thought to cause diarrhea in mink, lambs, calves, goats, and puppies.6 Proteus species colonize also amphibians and reptiles (water turtles) and are reported as a common inhabitant both in the oral cavity and in the cloaca.

Cockroaches are regarded as common vectors of different microorganisms, including P. mirabilis and P. vulgaris, carrying them on their bodies and posing a threat of their dissemination, food contamination, and spoiling as well as infection of humans. Other insects which may carry Proteus species bacteria in the intestines are bees. It is suggested that the source of the bacteria is pollen consumption and bees in the colony are infected one by one during food exchange. Honey pollution by Proteus spp. may pose a threat to consumers.

The occurrence of P. mirabilis and P. vulgaris human pathogens in oysters and shrimp poses a health risk if the shellfish are consumed raw. Proteus species rods are found in marine fishes (Atlantic mackerel, tilapias) and marine animals (tiger shrimp, cobia marine fish, snubnose pompano marine fish, and ornate spiny lobster).7


  1. Microterrors. Tony Hart
  2. Molecular Detection of Foodborne Pathogens. Dongyou Liu
  3. Textbook of Microbiology & Immunology. Parija
  4. Case files: Microbiology. Eugene C. Toy, Audrey Wanger
  5. Essentials of veterinary bacteriology and mycology. Gordon R. Carter, Darla J. Wise
  6. The potential of selected Australian medicinal plants with anti-Proteus activity for the treatment and prevention of rheumatoid arthritis (2015)
  7. Significance and Roles of Proteus spp. Bacteria in Natural Environments. Dominika Drzewiecka Microb Ecol. 2016; 72(4): 741–758. via PubMed Central
Proteus, a Gram-negative bacterium from the family Enterobacteriaceae, and is part of the normal flora of human gastrointestinal tract.
Proteus mirabilis
Source: CDC

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