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:Interestingly, the entry of non-zippering pathogens, Salmonella typhimurium and Shigella flexneri, was found to be independent of clathrin (Bonazzi and Cossart, 2006), suggesting that pathogens have evolved alternate strategies to gain access to the intracellular environment.
Category: