Fresh overnight cultures of L. monocytogenes were mixed with a modified tryptone top agar(TTA,0.5% agar)and poured on a Luria Bertani bottom agar(LBBA,Luria Bertani broth(Neogen Corp.)with 1.5% agar)to create a bacterial lawn.<br>Filtrates were spotted(1 mL:10 mL, filtrate:host )onto the lawns of freshly prepared hosts in a row and incubated at 30 ° C for 18 to 24 h.<br>Clear spots of lysed agar were cut and suspended into phosphate buffer saline(PBS; Neogen Corp.),centrifuged,filtered,and stored as“spot filtrate”at 4 ° C.<br>
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