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:When the IF cells are mixed with paramecia, the bacteria are soon engulfed in the host digestive vacuoles, from which they escape to the host cytoplasm and penetrate the macronuclear envelope with the invasion tip (Fujishima & Fujita, 1985; Görtz & Wiemann, 1989; Iwatani et al., 2005).
Category: