sentence: Aliquots ( 7 μ l ) of 10-fold dilutions of colicin M ( 0.25 mg ml stock solution ) , phage T5 and phage ϕ 80 stock solutions , and a threefold dilution of an albomycin stock solution were spotted onto LB ( 10 g bacto tryptone , 5 g yeast extract , 5 g NaCl per l ) agar plates seeded with the strains to be tested , as described previously ( Braun et al ., 1974 ) .