Titering my lysates

Planning today's work:

Titering the phage lysates should be a no-brainer, but it's been a long time since I worked with phage so I'd better think things through before I do it.

I have 15 µl of each of 5 phage stocks ('lysates').  The original titers (plaque-forming units/ml, pfu/ml) are written on the tubes - they range from 6x10^5 pfu/ml to 2x10^11 pfu/ml.  But the lysates are probably quite old (maybe 2 years, maybe more), so their titers may have dropped a lot.

I think I'll do one poured-lawn plate of each, using an amount of lysate that should be about 1000 pfu according to the original titer.  And I'll do a spotted-lawn plate for each phage, using undiluted lysate  and a range of dilutions.

I'll dilute the lysates in the same YPS medium I've grown the cells in.  It has calcium and magnesium added so should be fine for typical phage.