for listeria monocytogenes component concentration______________________________________ difco bacto columbia blood agar base 39 g l difco bacto agar 5 g l sigma l0505 lithium chloride anhydrous 7 5 g l sigma f5879 ferric ammonium citrate 0 5 g l sigma c1511 colistin methane sulfonate 10 g l i u 11 500 mg eli lilly iii0814 ceftazidime acid pentahydrate 20 mg l______________________________________final ph 7 0 base layer 10 ml no horse blood overlay 5 ml 4 horse blood______________________________________ l monocytogenes selectively cultured on the surface of the overlay will lyse the blood in the overlay creating clear colorless zones surrounding the colonies easily visible when light from a normal light or ambient source such as a window transmitting light desk lamp etc is transmitted to the bottom of petri dishes holding the medium the following procedure is used to select and isolate l monocytogenes in a food source twenty five g portions of each test sample were inoculated into 225 ml listeria enrichment broth leb used by the fda and university of vermont uvm broth used by the usda food safety and inspection service fsis after 24 48 h incubation at 30 u00b0 c a 0 1 ml portion from each enrichment broth was plated on selective agars with the usda enrichment method mcclain and lee 39 s modification of uvm was used when testing extended beyond 24 h in this procedure a 0 1 ml portion from uvm was inoculated into 10 ml of uvm 2 which has an increased concentration of acriflavine hcla hemolytic ceftazidime lithium chloride agar the formula for this medium is.