Listeria spp. and Enterobacteriaceae Group in Sandwiches of Meat and Meat Products

Abstract

Aims: To evaluate the Egyptian street-vended sandwiches of meat and meat products for the presence of Listeria monocytogenes and Enterobacteriaceae group. To evaluate the microbiological quality of street-vended sandwiches of meat and meat products sold in Cairo-Egypt. Place and Duration of Study: Department of Food Microbiology, National Research Center, Cairo, at during the period of January 2011 to September 2012. Methology: Seventy sandwiches of meat and meat products including ten samples each of burger, hawawshi, kofta, liver, luncheon, sausages and shawerma sandwiches were randomly collected from the street-vendors and food shops in Great-Cairo governorate. Samples were investigated for their loads of Enterobacteriaceae counts as well as the presence of L. monocytogenes. Enterobacteriaceae counts was done using the conventional International method (FDA), however isolation and identification of L. monocytogenes was carried out using three different microbiological examination methods including classic selective conventional media, chromogenic media, as well as rapid identification method “food-system kits”. 168 isolates of Listeria spp were identified following the biochemical identification tests (Bergey’s Manual) and confirmed using Hi Listeria identification kits and latex test kits. Results: Enterobacteriaceae group were detected in 51% of the examined samples with an average counts of 37x102 cfu/g. Listeria spp. were detected in range between 24% and 36%, depended on the method used, with numbers ranged from 16x102 to 23x102 cfu/g. All samples that were contaminated with Listeria spp. harboured L. monocytogenes. Listeria spp. was not detected in all the examined Hawawshi sandwiches with an exception of one positive sample detected using the chromogenic media. The obtained results indicated that 37 out 68 (54%) isolates, picked up from classic selective conventional media, and 62 out of 100 (62%) isolates from chromogenic medium were confirmed as L. monocytogenes indicating that chromogenic medium may be the superior for isolation of the pathogen from ready-to-eat sandwiches of meat and products. Conclusion: The obtained results indicated that these foods presented a source of infection to the consumer. Measures to control the quality of the raw material, environmental and hygienic conditions during preparation and serving should be taken. The chromogenic media was the most efficient for the isolation of the pathogen during this course of study.