الفهرس 
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Abstract
In the present study, 150 random samples of raw meat were collected from various butcher’s and retail’s shops in Assiut city Egypt. The samples were tested for the presence of Salmonella spp., E.coli serotypes and Listeria spp.
The bacteriological examination of the meat samples revealed that 29 samples were positive for Salmonella spp. with an incidence (19.33%) identified as, Typhimurium (27%), S. Enteritidis (31%), S. Infantis (20%) and S. Tevei (6.8%) S. Kentukey (3.4%), S. paratyphi A (3.4%), S. Heidel burg (3.4%) and S. Tokoradi (3.4%).
Also, 36 samples (24%) were positive for E. coli; represented as EHEC strains O157:H7, O111:H2, O26:H11 and O55:H6 incidence were 2.77%, 11.11%, 16.16% and 2.77%, respectively. ETEC strains O127:H2, O124 incidence were 13.88%, 2.77% respectively. The other serogroups of E. coli EIEC strains O124, (5.55%). The last strains of EPEC incidence were O17:H18, O146: H21, O78, O8, O1: H7, O135:H2 and O114: H4 were 5.55, 5.55, 8.33, 2.77, 2.77, 2.77 and 2.77 % respectively.
Additionaly, 40 isolates of Listeria spp. with a percentage (26%) were isolated and represented as L. monocytogenes (35%), L. innocua (25%), L. ivanovii (17.5%) and L. grayi (10%), L. welshimeri (7.5%) and L. seeligeri (5%).
Moreover, Chitosan NPs and OEO loaded chitosan NPs were prepared and then characterized by Zeta sizer, FTIR and TEM.
The antibacterial activity of OEO, chitosan NPs and OEO loaded chitosan NPs was evaluated against the isolated strains of S. Typhimurium, E. coli O157:H7 and L. monocytogenes.
The antibacterial activity of OEO loaded chitosan NPs was investigated against S. Typhimurium, E. coli O157:H7 and L. monocytogenes in meat samples. The findings revealed that in the presence of Chitosan NPs (MIC1), the mean reduction rate after 24, 48 hours of storage period were (99.25 and 99.8 %), (99.5 and 100%) and (95.71and 99.57) for S. Typhimurium, E. coli serotypes, and L. monocytogenes, respectively. Moreover, In the presence of a dose equal to MIC2, the reduction rate values were equal to (99.75, 100%), (99.75, 100%) and (99.99, 100%) for S. Typhimurium, E. coli O157:H7, and L. monocytogenes, respectively. In the presence of OEO loaded chitosan NPs (MIC1), the reduction rate were (99.98, 100%), (99.75, 100%) and (98.57, 99.99%) for S. Typhimurium, E. coli O157:H7 and L. monocytogenes, respectively. In the presence of a dose equal to MIC2, the reduction rate values were (100, 100%), (99.93, 100%) and (99.96, 100%) for S. Typhimurium, E. coli O157:H7 and L. monocytogenes, respectively.
Furthermore, compared to the control and usage of OEO, a statistically significant reduction (P < 0.05) was noted in the reduction rate of bacterial growth of MIC1 and MIC2 of Chitosan NPs and OEO loaded chitosan NPs for the all tested strains.
Public health significance of the isolated food poisoning microorganisms, Salmonella spp. E. coli serotypes and Listeria spp. as well as methods for protecting consumers were discussed.