Since the M13K07 contains a Kanamycin resistance gene, the phage titer can be easily measured by infecting F+ cells and plating on kanamycin containing LB plates.

Dear Serge, thank you very much for your answer. We use TG-1 platelet on Minimal Medium 9 to keep the cells expressing the F-pilus. We will try your suggestion next week. Thanks again & regards, Philipp

You'll have some cell debris with PEG precipitation. So titer by infecting F+ cells as Serge suggested is more accurate than absorbance. And it's easier than the top agar method, too.

I've always used top agar quantification, because the antibiotic resistance and the infection of F+ cells allow you to remove contaminants