Staphylococcus aureus bacteria were obtained in
freeze-dried form (ATCC, Manassas, VA). The cell pellet was
rehydrated in 1 ml LB (10 g tryptone, 5 g yeast extract, 5 g
NaCl per liter of distilled water, Sigma-Aldrich, St. Louis, MO)
and transferred to a test tube of 6ml fresh LB. Cells were
propagated at 37" C until they reached a stationary phase (24 h)
and were then passed to another tube of 6 ml LB at a 1:200
ratio. Once the second pass reached a stationary phase (24 h),
the second passage was frozen in one part LB and one part 50%
glycerol. This was used in cell experiments.