∞ generated and posted on 2017.03.19 ∞
∞ updated on 2022.06.05 ∞
Determinations of phage concentrations that are based on the ability of added phage virions to directly kill bacteria, as useful also for assaying phages that cannot replicate.
Please cite as:
Stephen T. Abedon
Killing Titer Calculator.
killingtiter.phage-therapy.org
Click here for calculator or see immediately below for further explanation and discussion.
| Crucial for this calculation is that either phage adsorption goes to a reasonable approximation of completion (e.g., > 95%) or instead you know what fraction has adsorbed. The latter, however, is not considered here in the calculation but instead adsorption to completion is assumed. Generally this means that phages have been given a fairly long amount of time to adsorb, e.g., not just a minute or two, and that bacterial concentrations are fairly high (e.g., 108/ml). For discussion of killing titers, see phage-therapy.org/writings/killing_titers.html. -------------------------------------- An error that might be commonly made is to assume that phage adsorption really will go to completion even if you are starting with relatively few bacteria (e.g., < 107/ml) and relatively short adsorption durations. Trust me on this, that's not going to happen unless you are willing to wait a fairly long period of time (e.g., hours, days, weeks, months, or even years depending on bacterial concentrations). It therefore can be helpful to compare killing titers with phage titers that are determined in a more 'traditional' manner. If the latter is significantly larger than the former, then your adsorption probably is not going to completion. For example, if your killing titer calculation is one of 106 phages/ml but your titer calculation using a plaque assay is 108 phages/ml, then you can be fairly sure that only 1% of your phages have adsorbed in the course of the assay. Alternatively, per the link above, if your killing titer determinations are greater than as determined using plaques, then it may be that phages have replicated to higher titers in the course of your determination. You also can compare calculated input multiplicities of infection (MOIinput) with calculated actual multiplicities of infection (MOIactual) using the Multiplicity of Infection Calculator to get a sense of whether bacterial concentrations and adsorption times are sufficient to achieve an approximation of 100% adsorption, i.e., such that MOIactual comes to approximation MOIinput. (With this killing titer calculator, however, the two are equal no matter what since 100% adsortion is assumied.) -------------------------------------- Lastly, don't forget to be consistent with your units. Mixing per milliliter with per liter, or absolute numbers with concentrations simply will not do! |