SIGNIFICANCE OF TEMPERATURE AND PREINCUBATION TEMPERATURE ON SURVIVALOF LISTERIA-MONOCYTOGENES AT PH 4.8

Listeria monocytogenes is a food-borne pathogenic bacterium that can b e found in soft cheese. At the beginning of cheese ripening, the pH is about 4.85-4.90. The aim of this work was to study the influence of t emperature, preincubation temperature (temperature at which the inocul um was cultivated) and initial bacterial concentration on the survival of L. monocytogenes (strain Scott A) at pH 4.8. It was demonstrated i n an earlier study that these factors did influence growth kinetics. S urvival studies of L. monocytogenes were done in a laboratory broth si mulating cheese composition. Four test temperatures (2, 6, 10 and 14 d egrees C) and two preincubation temperatures were studied (30 degrees C or the test temperature). Listeria monocytogenes (strain Scott A) wa s unable to grow at pH 4.8 under all conditions tested. The time for 1 0% survival was about 11 and 2 d, at 2 degrees C with preincubation at 2 degrees C and 30 degrees C, respectively; 9 d at 6 degrees C with p reincubation at 6 degrees C; 4 d at 6 degrees C with preincubation at 30 degrees C; and 1 d at 14 degrees C with preincubation at 14 degrees C or at 30 degrees C. The results show that survival of L. monocytoge nes (strain Scott A) at pH 48 is not dependent on initial bacterial co ncentration but on both the test and preincubation temperatures.