A comparison of the sterol content of multiple isolates of the Candida albicans Darlington strain with other clinically azole-sensitive and -resistant strains.

The mechanism of azole resistance of Candida albicans NCPF 3310 (the deposited culture of the Darlington strain) has been investigated but never fully explained. Seven isolates of this strain, from various sources, were examined by gas chromatography-mass spectrometry to detect changes in the sterol composition following passage through many laboratories over several years. Five of the seven, including one recently isolated from the patient, were found to be similar to each other in sterol content, containing large amounts of fecosterol. Of the remaining two, one was thought to be a sensitive variant, both produced only small quantities of fecosterol and resembled the normal clinical strains and other azole-resistant strains in sterol content. The sterol composition of the Darlington strain was unique and apparently stable to prolonged in vitro experimentation and passage through the patient.