The optical density (600 nm) of each well was recorded at 30-min intervals for
24 h. Duplicate samples of each MOI and control were used for the contemporaneous
enumeration of Salmonella bacteria and phages in the suspension at 1-h
intervals for 10 h and again at 24 h. For enumeration of salmonellas, decimal
dilutions of each suspension were spread plated (100 l) onto BG agar in
triplicate and incubated at 37°C for 24 h before examination for Salmonella
colonies. For bacteriophage enumeration, a 1-ml aliquot of each suspension was
subjected to centrifugation at 13,000 g for 5 min. The supernatant was then
filtered through a 0.45-m-pore-size filter to remove any remaining bacteria.
Decimal dilutions of this filtrate were prepared in SM buffer and subsequently
spotted (20 l) onto lawns of the appropriate Salmonella host as described above.