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:Autoaggregation and colony morphology changes induced by Ag43 (Diderichsen, 1980; Henderson et al., 1997a) occur only in certain genetic backgrounds (e.g. E. coli K-12) and are not pronounced properties of E. coli ML308-225 derivatives, a phenomenon probably related to the presence of different…
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