Ureaplasma urealyticum

Microbiology

Members of the family Mycoplasmataceae are small pleomorphic bacteria that characteristically lack a cell wall. Shapes range from filamentous to spherical, with diameters up to 0.8 μm. The genus Ureaplasma is biochemically unique in that all members possess urease and therefore hydrolyze urea to produce adenosine triphosphate. Ammonia, which increases the pH and limits growth in culture, is also produced. Ureaplasma urealyticum was first described in 1950 by Shepard, who noted minute colonies growing amid larger Mycoplasma colonies in specimens taken from the urethra and urine of men with nongonococcal urethritis. These bacteria were initially called T-strain Mycoplasma because of their tiny colony size. Urease production led to the name U. urealyticum .

U. urealyticum , a human pathogen, has historically been divided into 14 serotypes, which are divided into 2 distinct biovars based on biochemical and genetic features. Genetic study suggests that the 2 biovars represent 2 separate species; U. urealyticum biovar 1 ( Ureaplasma parvum ) includes serovars 1, 3, 6, and 14; and U. urealyticum biovar 2 is further divided into 3 subtypes. Subtype 1 includes serovars 2, 5, 8, and 9; subtype 2 includes serovars 4, 10, 12, and 13; and subtype 3 includes serovars 7 and 11. The entire genome of U. urealyticum has been sequenced. It is the smallest sequenced prokaryotic genome, except for Mycoplasma genitalium , and consists of only 75 DNA kilobase pairs.

Epidemiology

Ureaplasma spp. colonize the urogenital tract of healthy adults and adolescents. Ureaplasma spp. can be found on the mucosal surfaces of the cervix or vagina of 40%–80% of healthy women. Reported rates of asymptomatic urethral carriage of U. urealyticum among men typically range from 20%–50%; however, most studies have assessed only sexually active men in the context of urologic evaluation or sexually transmitted infection. One report found that urethral carriage was detected in only 8 (7%) of 114 asymptomatic male volunteers recruited from hospital staff and from primary care practices. Although colonization occurs less frequently among adolescents and young children, its presence is related to both sex and sexual activity. Foy and colleagues isolated Ureaplasma spp. from the urine of 1% of adolescent boys and 15% of adolescent girls; girls who reported dating members of the opposite sex were more likely to be colonized. The organism was not recovered from any of 101 children <13 years of age. Approximately 50% of colonized mothers transmit the organisms to their infants. Peripartum colonization occurs most often in infants born >1 hour following rupture of membranes and in those weighing <1000 g. Sites of infant colonization, in order of decreasing frequency, include the vagina, nasopharynx and throat, rectum, and conjunctiva. Colonization persisted at 3 months of age in 37%, 68%, and 33% of infants with initial vaginal, throat, or conjunctival colonization, respectively, in one study. Other studies have noted disappearance of peripartum colonization by 2 years of age.

Clinical Manifestations

A causal relationship between U. urealyticum and various clinical syndromes has been difficult to confirm, given the relatively high frequency of asymptomatic carriage and the difficulty in collecting samples from normally sterile sites. Many published studies have failed to adjust for potentially important confounding variables or were underpowered to detect significant associations. Nevertheless, U. urealyticum has been shown to cause urethritis. In pregnant women, Ureaplasma spp. have been implicated as a cause of chorioamnionitis, spontaneous abortion, stillbirth, preterm delivery, and postpartum endometritis. U. urealyticum also has been associated with long-term sequelae such as chronic lung disease in preterm infants. Invasive infections also have been reported, predominantly in neonates and immunocompromised individuals. The reported association with infertility in adults is controversial.