Prolonged stationary-phase growth of T-strain mycoplasmas in broth culture

The mycoplasmas

Images

Bromothymol blue broth: improved medium for detection of Ureaplasma urealyticum (T-strain mycoplasma)

Bromothymol blue (B) broth for the cultivation, detection, and identification of Ureaplasma urealyticum is described. In this medium, strains Cook and 960 had shorter generation times (60 min or less) and reached higher populations (over 10(8)) than have yet been reported for this species. Furthermore, the indicator changes color before the end of logarithmic growth, and the cultures retain viability for at least 1 day thereafter, greatly simplifying the handling of the organism. When the populations in cultures of these two strains and seven new isolates were determined, growth was detected earlier and proceeded to higher final titers in B broth than in urease test color medium (U-9 broth). The inclusion of antibiotics in B broth for use in clinical laboratories (B/NL broth) made the medium selective, specific, and more sensitive for the isolation of U. urealyticum. Comparison of B/NL broth with genital mycoplasma (GM) agar and U-9 broth for the primary isolation of U. urealyticum was made with 183 urethral swabs. All 70 isolates were detected on B/NL broth, but only 66 and 63 isolates were detected on GM agar and in U-9 broth, respectively. Moreover, the cultures in B/NL broth were pure and at titers that generally showed good correlation with colony counts on GM agar.

Effect of urea concentration on growth of Ureaplasma urealyticum (T-strain mycoplasma)

The effect of urea on growth of Ureaplasma urealyticum type VIII was studied by cultivating the organisms in a dialysate broth, prepared from soy peptone and autoclaved yeast, supplemented with 5% dialyzed horse serum, 100 mM 2-(N-morpholino)ethane sulfonic acid buffer (pH 5.75), and defined amounts of urea. Without urea, growth did not occur. Total growth was directly related to urea concentration. The least amount of urea that supported growth was 0.032 mM, which resulted in 3 x 10(4) colony-forming units per ml. The maximum yield of organisms, 8.0 x 10(7) colony-forming units per ml, was observed at 32 mM urea. Growth was limited not only by urea concentration, but also by the buffer capacity of the medium. The maximum amount of 2-(N-morpholino)ethane sulfonic acid buffer that could be employed was 100 mM; at higher concentrations, growth was inhibited. The yield of U. urealyticum was small even in medium with 32 mM urea and 100 mM 2-(N-morpholino)ethane sulfonic acid buffer: 0.63 mg of protein per liter of culture containing 5 x 10(10) total colony-forming units. The molar growth yield was 20 mg of protein per mol of urea. The growth rate was also a function of urea concentration. Generation times ranged from 8 h at 0.032 mM urea to 1.6 h at 3.2 mM urea, where the substrate level was saturating. The K(s) value for growth was 2.0 x 10(-4) M urea. Thus, urea is a growth-limiting factor for U. urealyticum, but remarkably large amounts of this substrate are required.

Effects of carbon dioxide, urea, and ammonia on growth of Ureaplasma urealyticum (T-strain mycoplasma)

By use of a simple device for continuous CO2 gassing of Ureaplasma urealyticum cultures growing in a liquid medium, we have been able to separate some of the effects of urea, CO2, ammonia, and pH on growth. The CO2 acted as a superior buffer in the pH range 5.7 to 6.8, which is optimal for Ureaplasma growth. It was, therefore, possible to observe the effect of repeated additions of urea to the culture without alkalinization of the growth medium. We found that the repeated additions of urea did not enhance Ureaplasma growth, and the resultant accumulation of ammonium ions (greater than 2,000 microng/ml) did not cause more rapid death under these conditions. By abruptly changing the gaseous environment from CO2 to N2, it was possible to cause a rapid pH change in the culture to a value above 8.0. This resulted in a more rapid death of the organisms.

Dialysis culture of T-strain mycoplasmas

Using dialyzing cultures of T-strain mycoplasmas, it was possible to make some observations relevant to the growth and metabolism of these organisms which would not be possible in nondialyzing cultures due to growth inhibition of the organisms by elevated pH and increased ammonium ion concentration in media containing urea. The rate of ammonia accumulation was found to be related to the initial urea concentration in the medium and could not be accounted for by any change in the multiplication rate of the organisms. More ammonia was generated than could be accounted for by the added urea alone, suggesting that an ammonia-producing activity other than urease may be present in T-strain mycoplasmas. Titers above 10(7) color change units per ml were achieved in dialysis cultures of a T-strain mycoplasma in the presence of urea, and such titers were maintained for approximately 60 h during dialysis culture in the absence of added urea.