Serial 10-fold dilutions of the filtered samples (100 l) were
combined with 100 l of fresh log-phase S. Typhimurium, 67.5 l of 1 M CaCl2,
and 3 ml of nutrient agar (5%) overlay (containing 50 g/ml nalidixic acid). The
phage-overlay solution was then added to nutrient agar plates and incubated
overnight at 37°C. One isolate from each wastewater treatment plant (n 14)
was plaque purified three times, suspended in SM buffer (0.1 M NaCl, 1 mM
MgSO4, 0.2 M Tris [pH 7.5], 0.01% gelatin) containing 1% chloroform, and
stored at 80°C until further use.