الفهرس 
ACKNOWLEDGEMENTOnly 14 pages are availabe for public view
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Abstract
A total of 225 cheese samples (Tallaga, Bramily and Ras cheese, 75 each) were collected from different dairy markets and shops in Assiut city, Egypt for the isolation of L. monocytogenes, Ps. aeruginosa and Staph. aureus.
The obtained results showed that Listeria spp. could be detected in 66.22% of the total examined samples, while L. monocytogenes was in 7.56%. Also, Pseudomonas spp. were detected in 43.11% of the examined samples, while Ps. aeruginosa was in 0.89%, and Staphylococci were detected in 41.78% of the examined samples, while Staph. aureus in 28% of the examined samples.
The isolates were identified using conventional methods, followed by PCR confirmation, in which 16S rRNA was positive for L. monocytogenes, 16S rDNA was positive for Ps. aeruginosa and 23S rRNA was positive for Staph. aureus.
Part II
(Experimental study)
Influence of some essential oils on the viability of the isolated potential pathogenic bacteria
The minimum inhibitory concentration (MIC) of the prepared cinnamon essential oil (CEO), rosemary essential oil (REO) and thyme essential oil (TEO) was detected in-vitro against the isolated L. monocytogenes, Ps. aeruginosa and Staph. aureus by using agar well diffusion method and tube dilution method, in which, the results revealed that the MIC were 1.56% for CEO, and 3.125% for both of REO and TEO.
Samples of Tallaga cheese were manufactured using MIC of the 3 prepared EOs separately. The CEO was the most effective against L. monocytogenes in which the count was decreased from 1.6 x 106 at 0 h to 5.5 x 102 during 1st week with reduction of 99.97%. Also, for Ps. aeruginosa, CEO, REO and TEO markedly reduced the count with the same reduction after curdling by 99.95%, although MIC of CEO was lower than MIC of both REO and TEO. Furthermore, the reduction done by CEO, REO and TEO on Staph. aureus was in parallel to the previous reduction for the studied L. monocytogenes and Ps. aeruginosa with reduction of 99.95% for CEO after 1st day.
The applied in-vivo study reflected the effectiveness of the used EOs against the investigated potential pathogenic bacteria. The sensory parameters of the manufactured cheese were of lower overall acceptability (OAA) in relation to the taste due to strong flavor of the used essential oil concentrations.