Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:…out using 20 ml of the following medium DY in a 22-mm-diameter test tube: 1 g of 2,6-dihydroxybenzoic acid, 1 g of yeast extract, 2 g of (NH4)2HPO4, 0.5 g of MgSO4·7H2O, 5 ml of metal solution (Uchida et al. 2003), and 5 ml of vitamin mixture (Yoshida et al. 2004a) in 1 l of tap water, pH 7.0.
Category: