الفهرس 
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Abstract
The study was done to investigate the foodborne pathogens and antimicrobial activities of essential oils.
Most of the foodborne pathogens were ubiquitous in nature as there is a possibility of cross contamination between one or several products during processing. Microbial foodborne infections occur when food contaminated with microbes is eaten and the bacteria continues to grow in the intestines,
setting up an infection which causes illness. Pathogenic foodborne were detected and evaluated in different foods samples. Different selective media were used as mentioned in material and methods to isolate and purify bacteria and fungi. These isolates were subjected to cultures and microscopic examination.
The bacterial isolates were found to be belong to eight species which included E. coli, Bacillus Cereus, Sal. Typhi, P. aeruginosa, S. aureus, Klebsiella pneumonia, Neisseria gonorrhoeae and Shigella bodyii. The isolated fungi were Asp. Flavus, Asp. Teries, Asp. Fumegatus, Asp. Niger, Fusarium, Fusarium, Rhizopus, Penicillium, Alternaria.
1) Seventy food samples were collected from different markets of health departments of ElSharkia governorate. According to the results, meat and poultry products were the most contaminated food type with foodborne pathogenic bacteria followed by dairy products, vegetable and fruit products and flour and bakery products respectively. While the least contaminated food type was canned products. Vegetable and fruit products were the most contaminated food type with fungi followed by bakery products, dairy products, Meat and poultry products.
2) Total count of bacterial and fungal isolates was estimated.
Seventy-six bacterial isolates were collected from different food samples. Bacterial isolates were identified using macromorphological characteristics on different specific media, micromorphological characteristics using gram stain and biochemical tests. According to identifications criteria, 21 isolates were identified as E. coli, 11 isolates as Samonella typhi, 6 as Shigella bodyii, 16 as Staphylococcus aureus, 7 as Bacillus Cereus, 9 as Pseudomonas aeruginosa, 3 as Neisseria gonorrhoeae and 3 as Klebsiella pneumonia.
3) Seventy-seven fungal isolates were recovered from different food sources. According to mirco and macromorphological criteria, 23 isolates were identified as Aspergillus flavus, 14 as Aspergillus terrus, 7 as Aspergillus fumigatus, 12 as Aspergillus Niger, 7 Fusarium, 7 Rhizopus, 5 Penicillium, 2 Alternaria.
4) Results of well diffusion assay revealed that most of tested essential oils possess antimicrobial activity against all isolated foodborne pathogenic bacteria and fungi except Olbanum and Cress which exhibit a weak inhibitory effect.
5) Lemongrass exhibited a great inhibitory effect against bacterial pathogens in approximately low concentrations especially against Pseudomonas aeroginosa (MIC 3.12 µl/ml and MBC 6.25µl/ml).
6) Similarly, Tea tree oil exposed its potency against fungal pathogens in extremely low concentrations especially against Aspergillus flavus with MIC value 1.56 µl/ml and MFC 3.12 µl/ml.
7) The mechanism of action of essential oils was analyzed by recording the changes in cell morphology and cell organelles of both tested pathogens using transmission electron microscope.
8) Results revealed that, lemongrass oil affected greatly P. aeruginosa cell morphology, they seem to be irregular with abnormal distribution of the cytoplasm and the cell wall became denser, moreover, part of the cytoplasmic material released through formation of cracks comparing with control rods cells that appeared normal, showing a multilayered cell surface consisting of an outer membrane, a peptidoglycan layer in the periplasmic space and a cytoplasmic membrane and cytoplasm was relatively uniform and that the plasma membrane was continuous close contact with the cell wall.
9) For Aspergillus flavus, cell wall and plasma membrane of the non-treated cells were smooth, uniform, surrounded by intact fibrillar layer and all organelles are suspended in highly dense cytoplasm having normal appearance while after tea tree oil treatment, cells showed remarkable accumulation of osmophil bodies closely under the plasma membrane which became rough and irregular with continuous folding in the cytoplasm and detachment of fibrillar layer. The hyphal tips were also collapsed and disintegrated.
10) Lemongrass and tea tree oils were purified and fractioned by TLC technique. The active antimicrobial fractions of lemongrass and tea tree oils were determined. The highest antimicrobial activity of lemongrass oil against Pseudomonas aeruginosa was obtained with active fraction of Rf value 0.45 with inhibition zone 46 mm. Whereas, tea tree oil exhibited the highest activity against Aspergillus flavus at Rf value 0.72 with 39 mm inhibition zone diameter.
11) Active fractions of both essential oils were analyzed using Trace GC1310-ISQ mass spectrometer (Thermo Scientific, Austin, TX, USA). GC-MS analyses revealed the most active fraction of the lemongrass oil was citral, and for TTO was Terpinen-4-ol.
12) The GC-MS chromatogram of lemongrass oil showed two high peaks at retention time of 12.9 and 13.8 min which was corresponding to 22 and 34% relative intensity. It was identified according to its molecular mass to be neral and geranial, respectively.
13) Citral (C11H16O), 3,7-dimethyl-2,6-octadienal, is a monoterpene aldehyde mixture of geranial, cis-isomers, and neral, trans-isomers, with 152.23 g/mol molecular mass.
14) Tea tree oil active fraction showed high peaks at retention time of 7.25 min which was corresponding to 15.21% relative intensity. It was identified according to its molecular mass 154.2493 to be Terpinen-4-ol (C10H18O), 4-methyl-1-propan-2-ylcyclohex-3-en-1-ol.
15) The inhibitory effect of (lemongrass oil and citral) & (tea tree oil and Terpinen 4-ol) on production of some food degrading enzymes by Pseudomonas aeruginosa and Aspergillus flavus, respectively were assessed. It was found that lemongrass and tea tree oils possess powerful inhibitory effect on production of proteinases, amylase, lipase and lactase enzymes with inhibition percentages among 80 and 90%.
16) Essential oils and their active compounds are considered a good choice for preservation of food and food products, as they safely inhibit microbial growth and destroy enzymes in microbes that cause food spoilage