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:This is in agreement with some results where different antibiotics led to less negatively charged zeta potential in Gram-negative bacteria as a consequence of modification or complete loss of LPS and/or lipid A from the outer membrane (Winfield et al., 2005; Gooderham and Hancock, 2009; Moffatt et al., 2010).
Category: