Inoculations were carried out from precultures grown for 24 h in trace iron GPP at inoculation rates of 0.1% v/v to minimize carryover of iron. The total initial cell counts of cultures
thus inoculated typically were 5 × 104 mL−1 and 3 × 103 mL−1 for C. albicans and C. vini, respectively. Incubation of flask cultures was carried out aerobically in a temperature-regulated shaker at 30 °C and 200 r.p.m. Media and stock solutions were kept in sterile plastic ware (polypropylene, Nalgene) for this work. Glassware used Saracatinib in vivo for incubations was first washed with a conventional detergent (Alconox, Fisher), followed by 24-h soaking in a 3% v/v solution of a commercial trace metal removal detergent (Citronox, Fisher) and nine rinses in deionized water. The growth of microorganisms was measured by following the OD600 nm of cultures in 1-cm light path cuvettes. For dry weight determinations, cells were harvested by centrifugation at 1200 g for 10 min and washed twice with deionized water. Then, the cell mass was determined after drying at 100 °C for 24 h, with cooling in a vacuum dessicator containing a granular desiccant (Drierite, Xenia, OH) on preweighed aluminium dishes
to a constant weight. The total cell counts were carried out using a 0.1-mm depth haemocytometer Selleck PLX4032 with improved Neubauer ruling (Brightline, Hausser Scientific, Horsham, PA). Trace iron and other trace metal concentrations in the media before and after extraction were determined in quadruplicate by high-resolution magnetic-sector old ICP-MS at the Environmental Chemistry & Technology and Wisconsin State Laboratory of Hygiene, University of Wisconsin-Madison. Table 1 shows the concentrations of iron and several other metals in the chemically defined medium prepared without any Fe addition before and after Fe extraction. Using an insoluble resin in a batch-contacting process, it was possible to reduce iron concentrations by >80% to 1.2 μg L−1 (0.021 μM) in the chemically defined medium used. The residual Fe content in the Fe-extracted medium was found to result in Fe-restricted growth for both C. albicans and C.
vini with increased lag phases and lower specific growth rates as compared with cultivations with added iron (Fig. 1a and b, respectively). Candida vini appeared to be more affected by low Fe concentrations than C. albicans. Accordingly, the maximum growth yields (Ymax) determined after 44-h growth exhibited a stronger dose dependence for added iron in the case of C. vini (Fig. 2). At the lowest iron concentration tested (0.02 μM), the maximum growth yield attained by C. vini was less than half the Ymax value obtained for C. albicans. The comparison of the effects of several iron chelators including the clinically relevant desferrioxamine and deferiprone at relatively low concentrations (0.25 g L−1) showed that the growth of C. albicans was not inhibited by desferrioxamine in comparison with the control treatment with no added iron chelator (Fig. 3).