Isolation and Identification of Listeria monocytogenes from Retail Meats in Beijing.

To determine the contamination of retail meats by Listeria monocytogenes in Beijing, 70 meat samples (25 pork, 10 beef, 14 lamb, and 21 chicken) were analyzed between January and March in 1990. Eight (11%) samples were positive for L. monocytogenes , and 39 (56%) samples were found to contain other Listeria spp. Seven pork and one chicken sample contained L. monocytogenes , whereas all beef and lamb were free of L. monocytogenes . Meanwhile, 15 (60%) pork, 11 (52%) chicken, 7 (70%) beef, and 6 (43%) lamb samples were positive for other Listeria spp. The eight confirmed isolates of L. monocytogenes were serologically typed. Six (5 from pork and 1 from chicken) were serotype l/2a, and the other two isolates (2 pork) were serotype l/2c and l/2b. No isolates were of serotypes 3 and 4. All positive samples for L. monocytogenes were frozen meats, and the incidence of Listeria spp. was greater for frozen samples than for fresh. Sixty of 70 samples (22 pork, 8 beef, 11 lamb, and 19 chicken) were used to compare the effectiveness of Oxford medium and Palcam medium for the isolation of L. monocytogenes from meat samples. L. monocytogenes was isolated from seven samples by Palcam medium, while five samples were positive by Oxford medium, indicating that Palcam medium was more effective for recovering L. monocytogenes than Oxford medium.