Effect of polyoxyethylene sorbate compounds (Tweens) on colonial morphology, growth, and ultrastructure of Mycobacterium paratuberculosis.

Polyoxyethylene sorbate (Tween) compounds were tested to compare their growth stimulation effects on Mycobacterium paratuberculosis. Three low passage and three high passage clinical isolates and ATCC strain 19698 were used. Tween 20, 40, 60, and 80 were tested at concentrations of 0, 0.001, 0.01, 1.0, and 3.0% (w/v) in radiometric broth culture media and in Middlebrook 7H9 agar plates. Scanning and transmission electron microscopy were used to examine cell wall appearance and ultrastructure, respectively. In broth culture, 0.1% (w/v) Tween 60 most dramatically enhanced growth of M. paratuberculosis ATCC strain 19698. The effects of Tween 40 and 80 on growth took a bimodal form, enhancing growth at concentration ranges of 0-0.01% and 0.1-1.0% (w/v) but suppressing growth at concentrations of 0.01-0.1% (w/v). Two of three high passage clinical isolates grew optimally in the presence of 1.0% (w/v) Tween 80, while the remaining high passage isolate and all three low passage isolates grew best in media containing 0.1% (w/v) Tween 80. Colonial morphology of all strains grown on Middlebrook 7H9 agar without Tween 80 was irregular and granular whereas colonies on plate media containing greater than 0.01% (w/v) Tween 80 were entire, smooth, and domed. Scanning electron microscopy also revealed a transition from rough to smooth cell walls with increasing Tween 80 concentration. Transmission electron microscopy showed the presence of low electron dense intracellular vacuoles in Tween 80 grown M. paratuberculosis cells. Thus, Tweens altered colonial morphology, the cell wall surface, and ultrastructure of M. paratuberculosis and stimulated its growth in vitro in a concentration-dependent, and often bimodal, fashion.(ABSTRACT TRUNCATED AT 250 WORDS)