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:These bacteria encase themselves in a hydrated matrix of polysaccharide and protein, causing their inherent resistance to antibiotic therapy, neutrophil function, phagocytes, and antibodies.(18,19) Another part of this biofilm that is composed of hostderived glycoproteins, such as fibrinogen, fibronectin, collagen, and laminin, enhances bacterial adherence to foreign material.
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