Virus dilution

Virus replication usually yields such quantities that titers are determined firstly by making accurate serial dilutions of virus suspensions, before assay.  Dilutions are usually in two-, five- or ten-fold series depending on the virus, and use a suitable diluent such as cell culture medium or phosphate-buffered saline (PBS). It is important to avoid  bacterial contamination (the virus assay may use cultured cells) by ensuring the use of aseptic technique and  sterile diluent, tubes, pipettes or pipette tips  for the  transfer of volumes between each dilution. Thorough mixing of each dilution before further transfer is essential and  must be done using a fresh  tip to avoid  carrying additional virus  into  the  new dilution from any liquid coating the outside surface of the tip (a microliter can carry several millions of virions, causing inaccuracies in the final titer). Once diluted, virus should be assayed as soon as possible, as most viruses rapidly lose infectivity at room temperature. All the assays described here would examine several dilutions at one testing, and each dilution would be tested in duplicate (at least) to allow for a mean titer to be derived, improving accuracy and compensating for experimental inaccuracies.