Ureaplasma (urea form) are eubacteria which belong to the class Mollicutes. The class Mollicutes was established in the 1960s to include the mycoplasmas and related organisms and it now contains four orders, five families, eight genera, and more than 200 known species that have been detected in humans, vertebrate animals, arthropods, and plants. Originally, Ureaplasma were called "T-mycoplasma", but later the genus Ureaplasma was designated in view of their use of urea as a metabolic substrate. Humans are the primary host for Ureaplasma parvum (small, referring to its significantly smaller genome sizes compared to Ureaplasma urealyticum) and Ureaplasma urealyticum (urea-dissolving or urea-digesting) species.

Unique Features

While similar to mycoplasma (fungus form) in many respects, Ureaplasma are nutritionally unique, possessing the enzyme urease which splits urea. Another unique feature is associated with a higher concentration of cholesterol within the cell membranes protecting from the antibacterial activity of defensins. The lack of defensin killing effect may explain why Ureaplasma are commonly isolated from the canine genital tract, where it is present as normal microflora 7.

Large-sized Ureaplasm urealyticum, otherwise known as T-mycoplasma, colony.

Ureaplasma do not have cell walls and are thought to be the smallest free-living, self-replicating cells. They are limited by the lack of cell wall to a parasitic existence in eukaryotic cells.

Pathogenic Ureaplasma

Ureaplasma species are the most common bacteria implicated in human urogenital infections in men including male urethritis, prostatitis, epididymitis, urinary calculi, and pyelonephritis. Ureaplasma urealyticum is the most common microorganism found in infertile men and has been associated with a significantly lower sperm concentration 4.

In women, Ureaplasma causes bacterial vaginosis, infertility, spontaneous abortion, prematurity/low birth weight, intrauterine growth retardation, and postpartum/postabortion fever. It may indeed be an "underestimated enemy of human reproduction." Known transmission routes involve sexual contact or maternal-infant transfer. Ureaplasma has been implicated in neonatal disease and mortality including congenital pneumonia, preterm delivery, low birth weight and intrauterine growth retardation and it is thought to infect or colonise up to 37% of newborns 1,2.

Ureaplasma species are commonly isolated from respiratory secretions, gastric aspirates, blood, cerebrospinal fluid, lung and brain tissue. A role for Ureaplasma in neonatal brain injury is supported by recent studies in experimental animal models.

Clinically, Ureaplasma species have been isolated directly from kidney stones and have been linked to the formation of infection stones in the urinary tract, mediated by urease activity 3.

Ureaplasma Species In Domestic Animals

Named Ureaplasma species isolated from domestic animals include Ureaplasma canigenitalium (dog), U. felinum (cat), U. gallorale (poultry), and Ureaplasma species (sheep and goats). In cattle, Ureaplasma diversum has been isolated from herds with conjunctivitis.

Ureaplasma organism are among the few bacterial species causing sexually transmitted diseases in male dogs which include Mycoplasma and Brucella species. In addition, dog breeds, genetically predisposed to the formation of urinary stones, are more susceptible to urinary tract infections with urease-producing bacteria such as Ureaplasma 6. These organisms make the urine more alkaline which leads to precipitation of mineral ions, formation of crystals and urinary stone formation.


  1. Ureaplasma species: Role in Diseases of Prematurity
  2. Does Ureaplasma spp. cause chronic lung disease of prematurity: Ask the audience?
  3. Mycoplasmas and Ureaplasmas as Neonatal Pathogens
  4. Armand Zini, Ashok AgarwalSperm Chromatin: Biological and Clinical Applications in Male Infertility
  5. The Canine Oral Microbiome
  6. Albrecht Hesse, Reto Neiger. A Colour Handbook of Urinary Stones in Small Animal Medicine
  7. Yongming Sang, M. Teresa Ortega, Frank Blecha, Om Prakash, and Tonatiuh Melgarejo. Molecular Cloning and Characterization of Three Β-Defensins from Canine Testes


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