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:jejuni 81-176, a virulent strain able to produce gastroenteritis in human volunteers and promote commensal colonization of the chick gastrointestinal tract (Black et al., 1988; Hendrixson and DiRita, 2004).
Category: