الفهرس 
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Abstract
Staphylococcus species cause various diseases in animals and humans. This study investigated the prevalence of Staphylococcus spp. in animals and human samples in Beni-Suef Governorate, Egypt, determining their antimicrobial resistance profile, detecting some resistance and virulence-associated genes in multidrug resistant (MDR) isolates and studying the antibacterial effect of carvacrol oil on the MDR isolates and their resistance genes expression. A total of 216 samples were collected aseptically from subclinically mastitic cow’s milk (n=100), sheep abscesses (n=25) and human (n=91). A total of 154 Staphylococcus species were isolated (71.3%) represented as 75%, 52 and 72.5%, respectively. The most frequent bacterial isolates were S. aureus (42.9%), followed by S. schleiferi (25.3%), S. intermedius (12.3%), S. xylosus (11.7%), S. haemolyticus (4.5%), S. epidermidis (1.9%) and finally S. aurecularis (1.3%). Haemolytic activity and biofilm production were detected in 76.6 of isolates, respectively. Antimicrobial susceptibility testing of isolates showed high degrees of resistance to the most commonly used antimicrobials in human and veterinary practices. Application of PCR on MDR isolates revealed the presence of mecA, vanA, vanC1 resistance genes in 100,50 and 83.3% of isolates, respectively. Moreover, hla, icaA and icaD virulence genes were detected in 50, 83.3 and 75% of isolates, respectively. Additionally, spa gene was found in 58.3% of the tested S. aureus isolates, respectively. Carvacrol oil effectively inhibited the growth of all the tested isolates at concentrations of 0.1, 0.05 and 0.04% and 0.03% (MIC), 100% were inhibited Interestingly, some phenotypic changes were observed upon treatment with concentration of 0.02% carvacrol oil. All the treated MDR staphylococcus isolates were changed to either susceptible/intermediate susceptible to 2-3 antimicrobials than the parental bacterial isolates. Real-time PCR was applied for detection of differential expression of mecA and vanC1 genes before and after treatment with carvacrol oil revealed a mild reduction in both genes expression after treatment with fold changes ranged between 0.07-0.27 folds. It was concluded that staphylococci are more likely to spread from humans to animals and vice versa. Also, carvacrol and other EOs may be considered as a promising natural alternative to conventional antibiotics to be used to combat pathogens impacting human health and agriculture.