Mass spectra of ADD standard and the cholesterol metabolite produced by R. equi USA-18ΔB8. The strain was cultivated in medium containing 0.2% cholesterol and 0.2% Tween 20 at 37°C, 200 rpm, for 8 days. The broth was extracted with ethyl acetate and the extract was analyzed by HPLC and tandem mass spectrometry. (A) ADD standard, (B) the metabolite with retention time of 5.3 min in the HPLC profile (see Figure 4). The spectrum in the upper half of a panel indicates the molecular weights of the analyzed compounds, while that in the lower half shows the fragmentation pattern of the compound with 285.2 m/z.