Simple method to observe the adaptive response of Listeria monocytogenes in food.
A simple, novel method for determining stress-adaptive response of Listeria monocytogenes in food systems is presented. The method involves plating samples on Listeria-selective agar (LSA) acidified to pH 5.25 with incubation at 36 degrees C for 60 h to detect acid adaptation and plating on LSA with 70 gl-1 NaCl and incubation at 7 degrees C for 7 d to detect cold-osmotic adaptation. Adapted cells produced larger colonies (> 1 mm) under these conditions than unadapted cells. Scot A (97%) and Brie-1 (100%) cells incubated in milk at pH 5 for 3 h manifested the acid-adapted colony type compared with 6% and 21% of viable cells in the unstressed control population. After a 5-d adaptation period at 4 degrees C in milk with 80 gl-1 salt, 29% of Scot A and 91% of Brie-1 viable cells exhibited the adapted colony type compared with < 1% of the unstressed control population. Stress-adapted L. monocytogenes were isolated from soft cheese held for 42 d at 10 C.
Bolton
L F
LF
Department of Food Science and Technology, University of Georgia, Athens, GA, USA.
Frank
J F
JF
D000222:Adaptation, Physiological; D000818:Animals; D001431:Bacteriological Techniques; D002611:Cheese / Q000382:microbiology*; D003080:Cold Temperature; D003470:Culture Media; D006863:Hydrogen-Ion Concentration; D008089:Listeria monocytogenes / Q000254:growth & development*; D008892:Milk / Q000382:microbiology; D012965:Sodium Chloride
D003470:Culture Media; D012965:Sodium Chloride