In this exercise, you have the opportunity to: (1) amplify (increase the numbers of) phages in the sewage sample by allowing them to infect and reproduce within fresh E. coli, (2) collect the phages from the culture by centrifugation and filtration, and (3) detect and titer the amplified, isolated phages using a plaque assay. The assay is based on the fact that each plaque on a lawn of bacteria, although it contains 106 to 107 virions along with bacterial debris, represents a single infecting phage that entered one cell at the start of the culture. The infection then “spread” as the viruses reproduced and cells lysed, eventually forming a visible plaque (figure 37.3). The titer of a phage suspension, therefore, is determined
by counting the number of plaques that form from a given volume of suspension. Phage titer is expressed as laqueforming
units (PFU) per milliliter (ml).
In this exercise, you have the opportunity to: (1) amplify (increase the numbers of) phages in the sewage sample by allowing them to infect and reproduce within fresh E. coli, (2) collect the phages from the culture by centrifugation and filtration, and (3) detect and titer the amplified, isolated phages using a plaque assay. The assay is based on the fact that each plaque on a lawn of bacteria, although it contains 106 to 107 virions along with bacterial debris, represents a single infecting phage that entered one cell at the start of the culture. The infection then “spread” as the viruses reproduced and cells lysed, eventually forming a visible plaque (figure 37.3). The titer of a phage suspension, therefore, is determinedby counting the number of plaques that form from a given volume of suspension. Phage titer is expressed as laqueformingunits (PFU) per milliliter (ml).
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