Morphology of Ureaplasma urealyticum (T-mycoplasma) organisms and colonies

Abstract

The morphology of U. urealyticum in broth cultures was studied by phase-contrast microscopy. Most organisms appeared singly or in pairs. Long filaments and long chains of cocci, common in classical mycoplasma cultures, were not observed. On solid medium U. urealyticum produced fried-egg colonies which developed according to the previously suggested scheme for the morphogenesis of the classical mycoplasma colonies. The formation of the peripheral zone of the colonies followed that of the central zone only when growth conditions were adequate. Hence, the appearance of peripheral zones, and consequently the larger colony size, can be taken as an indicator of improved growth conditions. Incubation in an atmosphere of 100% CO2 resulted in significantly larger colonies than in an atmosphere of N2, O2 or air. CO2 acts as a buffer, keeping the pH at the optimal range for Ureaplasma growth (pH 6.0-6.5) in the presence of the NH3 produced from the urea hydrolyzed by the organisms. The addition to the medium of 0.01 M urea with 0.01 M putrescine enabled better growth than with urea alone. Small amounts of phosphate improved growth in a CO2 atmosphere, apparently fulfilling a nutritional role. Under N2 higher phosphate concentrations were required for good growth, apparently serving as a buffer and a nutrient. NaCl and sucrose which were added to increase the tonicity of the medium inhibited growth > 0.1 M. An increase in the agar concentration > 2% resulted in decreased colony size. Likewise, prolonged drying of the agar plates caused a marked decrease in colony size, mostly affecting the peripheral zone. The addition of urea and putrescine to the growth medium and incubation in a humidified CO2 atmosphere are recommended for improved growth and formation of fried-egg colonies of U. urealyticum on agar. These experiments were carried out with a laboratory-adapted strain.