الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Ready to Eat (RTE) foods are types of foods that require no further cooking by the consumer. These include salads, dairy products, ready- to- eat deli meats, raw fruits and vegetables. Nowadays RTE foods are being consumed in increasing quantities due to the worldwide change in life style toward both easily and quickly prepared.
Listeriosis caused by L. monocytogenesis low in incidence but its mortality rate can be as high as 30%. The ability to persist in food-processing environments and multiply under refrigeration temperatures makes L. monocytogenes a significant threat to public health. The presence of Listeria species in food is an indicator of poor hygiene. In animals, L. monocytogenes and L. ivanovii may cause septicemia, meningoencephalitis and abortion.
This study aimed at studying the occurrence of L. monocytogenesin RTE foods and salads in some Alexandria markets. A total of 250 RTE samples were equally collected from East, Centre, West, Montazah, and Amriyah districts of Alexandria governorate, Egypt. Fifty samples were collected from each target area (20 salads, 24 processed meats and poultry products, 6 sandwiches).
Collected samples were subjected to L.monocytogenesisolation and identification procedure according to FDA-BAM. selective enrichment of L. monocytogenes on BLEB was done, followed by simultaneous culture on Oxford and chrOMagar plates for 48 H at 37oC.Suspected colonies on either of them were subcultured on TSAYE agar for more purification of isolate before subjecting it to biochemical confirmatory tests.
The present study showed the following results
1. Out of 250 RTE food samples, 42.8% recovered Listeria spp. On Oxford agar, 98 samples (39.2%) were positive for Listeria spp. On chrOMagar, only13 samples had the typical colony morphology of L. monocytogenes/ivanovii (5.2%) and 41 were Listeria spp. other than monocytogenes/ivanovii (16.4%).
2. No L. monocytogenes were recovered from samples after biochemical confirmatory tests were applied to all the suspected colonies from Oxford and chrOMagar.
3. The isolation of Listeria spp.showed significant difference between districts of collection (p<0.005).
4. There was no significant association between the type of RTE food and the isolation of Listeria spp.
5. There was a significant association between the type of processed meat and Listeria isolation (p=0.022). The most contaminated type of processed meat by Listeria spp. were luncheon samples (14.2%) followed by pastrami by the isolation rate of 11.7%. All isolates of L.ivanovii(n=5) were recovered from pastrami samples, and these contributed to 4.2% of all pastrami samples.
6. Kappa test showed a poor agreement between Oxford agar and chrOMagar.
7. There was no statistically significant difference in rate of Listeria spp. isolation and storage temperature.
In conclusion, Listeria spp. as a poor hygiene marker were present in more than 40% of studied RTE food samples which denotes poor sanitary condition of the RTE food samples. This was particularly true for luncheonsamples regarding Listeriaspp isolation, and pastrami samples which were the highest in L. ivanoviiandL.seelgeriisolation. The low specificity of chrOMagar does not allow it to be a sole diagnostic culture medium for Listeria spp. If chrOMagar is to be used, biochemical tests should follow it for confirmation.