الفهرس 
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Abstract
7. It is important to note that the presence of enterotoxigenic Staphylococcus aureus in cheese products poses a potential health risk. Consumption of contaminated cheese can lead to staphylococcal food poisoning. Therefore, 120 random cheese samples including damietta, kariesh, spreadable processed, and Ras cheese (30 samples of each) were collected from different supermarkets and street- vendors at Kafr El-Sheikh governorate for detection of enterotoxigenic Staph. aureus, identification of MRSA strains through detection of mecA gene using PCR technique and studying antibiotic susceptibility test for isolated strains. In addition, studying the impact of natural additives, such as nisin, lactoferrin, and thyme oil on the growth and viability of the isolated enterotoxigenic Staph. aureus during the manufacturing process of kariesh cheese.
The obtained results summarized in the following items:
7.1. Incidence of Staph. aureus in cheese varieties.
Staphylococcus aureus was found in Damietta, kariesh, processed cheese, and Ras cheese at rates of 20%, 23.33%, 26.67%, and 26.67%, respectively. The overall incidence rate of staph. aureus in all examined cheese samples was 24.17%.
Incidence of coagulase- positive Staphylococcus aureus in the examined Damietta, kariesh, processed cheese, and Ras cheese samples were 6.67%, 16.67%, 13.33%, and 13.33%, respectively. The overall incidence rate of coagulase-positive Staphylococcus aureus across all cheese samples was 12.5%.
According to Egyptian standards, 93.33%, 83.33%, 86.67%, and 86.67% of the examined Damietta, kariesh, processed cheese, and Ras cheese samples, respectively, were following these standards.
Occurrence of 23S rRNA in 10 out of 15 Staphylococcus aureus isolates from tested samples of damietta, kariesh, processed cheese, and Ras cheese were 6.67%, 10%, 6.67%, and 10% respectively. Furthermore, Seb was detected in a single Staphylococcus aureus isolated from kariesh, processed cheese, and Ras cheese, while Sea could not detect in examined Staph. aureus isolates.
MRSA phenotypically, and genotypically was detected in 8.33%, and 8.33% of examined Staph. aureus strains isolated from all examined cheese samples. mecA gene was detected in the examined Staph. aureus strains from damietta, kariesh, processed, and Ras cheese, with percentages of 6.67, 10, 6.67, and 10% respectively with overall prevalence in all examined samples was 8.33%.
All MRSA isolates were resistant completely(100%) to amoxicillin, while the most effective antimicrobials against MRSA isolates were chloramphenicol, streptomycin, rifampicin, and erythromycin showing sensitivity 100% for each type.
all MRSA isolates resistant for more than three antibiotics with MAR index ranged from 0.27 to 0.63.
7.2. Antibacterial effect of natural additives to control growth and viability of inoculated Staph. aureus during kariesh cheese manufacturing:
7.2.1. Nisin (10 ppm, 12.5 ppm):
Staph. aureus count in kariesh cheese with 1% salt treated with 10 ppm nisin decreased from 8.28± 0.02 to 6.43± 0.08 cfu/gm on the 15th day, resulting in a reduction of 14.15%. Similarly, when treated with 12.5 ppm nisin, the count decreased from 8.26± 0.02 to 6.09± 0.09 cfu/gm on the 15th day, with a higher reduction percentage of 18.69%.
Staph. aureus count in kariesh cheese with 5% salt treated with 10 ppm nisin decreased from 8.27± 0.01 to 5.97± 0.03 cfu/gm on the 15th day, resulting in a reduction of 19.32%. Similarly, when treated with 12.5 ppm nisin, the count decreased from 8.26± 0.01 to 5.75± 0.03 cfu/gm on the 15th day, with a higher reduction percentage of 22.29%.
7.2.2. Lactoferrin (10 and 20 ppm):
The count of Staph. aureus in kariesh cheese with 1% salt treated with 10 ppm lactoferrin decreased from 8.29± 0.02 to 6.84± 0.02 cfu/gm on the 15th day, resulting in a reduction of 8.67%. Similarly, when treated with 20 ppm lactoferrin, the count decreased from 8.27± 0.01 to 6.42±0.09 cfu/gm on the 15th day, with a higher reduction percentage of 14.28%.
Staph. aureus count in kariesh cheese control group with 5% salt decreased from 8.27± 0.01 to 7.40± 0.02 cfu/gm on the 15th day. However, when treated with 10 ppm lactoferrin, there was a gradual decrease in the staphylococcal count from 8.28± 0.01 to 6.01± 0.05 cfu/gm on the 15th day, resulting in a reduction of 18.78%. Similarly, with treatment using 20 ppm lactoferrin, the count decreased from 8.27± 0.01 to 5.91± 0.02 cfu/gm on the 15th day, showing a higher reduction percentage of 20.13%.
7.2.3. Thyme oil 1%:
Staph. aureus count in kariesh cheese with 1% salt and treated with 1% thyme oil, on the 15th day of storage, the count decreased from 8.29 ± 0.01 to 6.94 ± 0.02 cfu/gm, resulting in a reduction of 7.34%. In comparison to the control group which showed a decrease from 8.29 ± 0.01 to 7.49 ± 0.05 cfu/gm on the 15th day.
Also, the decline in Staph. aureus count in kariesh cheese with 5% salt and treated with 1% thyme oil, on the 15th day of storage, was from 8.29 ± 0.01 to 6.27 ± 0.11 cfu/gm, resulting in a reduction of 15.27%, compared to the control group that exhibited a decrease from 8.27 ± 0.01 to 7.40 ± 0.02 cfu/gm on the 15th day.