الفهرس 
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Abstract
The current study was carried out in Beheira province for a period of 8 months from November 2016 to June 2017 for isolation, identification and molecular characterization of methicillin resistant Staphylococcus aureus from human and dairy cattle.
A total of 127 nasal and hand swabs were randomly collected from healthcare workers (89) and farm workers (38). Samples of healthcare workers were collected from 4 different hospitals mainly from surgical department. Data of each sample was recorded including; sex, age, health status, last antibiotic intake, animal contact, exposure to sterilization and presence of skin lesions. In addition, a total of 266 different samples were collected including nasal swabs of from dairy cattle (135), milk (89) and milking machine swabs (42). Bacteriological examination of the collected samples was carried out at the Laboratory of Animal Health Research Institute (AHRI), Behera branch. Isolation of MRSA was attempted on ORSAB and the obtained isolates were identified by biochemical tests. Also, the antibiotic sensitivity of the obtained isolates was investigated. Finally, MRSA isolates were screened by PCR for presence of mecA, mecC and PLV genes.
The recorded results showed that the overall estimated prevalence of MRSA in the examined human and cattle samples was 31.5 and 48.87%, respectively. Concerning human samples, the effects of some demographic factors on the estimated prevalence of MRSA were studied and revealed the following:
• The effect of nature of occupation on the estimated prevalence of MRSA clarified that the prevalence of MRSA healthcare workers and farm workers was 29.2 and 36.8%, respectively.
• Sex related prevalence showed that females (32.05%) had slightly higher prevalence than males (30.61%).
• The age wise positivity of MRSA in the examined human samples cleared that the age group (20 – 40 years) scored the highest MRSA prevalence (38.46%) followed by the age group (> 40 years) (23.25%) and lastly the age group (< 20 years) (0.0%) that was in harmony with the active age of working.
• The recorded prevalence of MRSA in relation to health status of the examined workers clarified that both apparently healthy workers and those with history of chronic diseases had MRSA with prevalence of 34.4 and 23.53%, respectively.
• The effect of animal contact on the prevalence of MRSA showed that the group with history of animal contact (30.67%) had slightly lower prevalence than the other group with history of no animal contact (32.69%).
• Prevalence of MRSA in healthcare workers in relation to contact with different animal species revealed that workers with history of cattle contact scored the highest prevalence (100%) followed by those with history of pet animals contact (27.27%) then those with history of poultry contact (20.83%) and lastly those with history of equine contact (0.0%).
• Prevalence of MRSA in farm workers in relation to contact with different animal species revealed that workers with history of poultry contact scored the highest prevalence (56%) followed by those with history of equine contact (40%) then those with history of cattle contact (36.84%) and lastly those with history of pet animals contact (0.0%).
• The effect of application of antiseptics by health workers under investigation on the prevalence of MRSA showed that workers informing that they used antiseptics had higher prevalence (33.33%) that those informing that they did not use antiseptics (20.69%).
• All farm workers under investigation informed that they did not use any antiseptic during their work and all of them were positive for presence of MRSA with a prevalence of 36.84%.
• The prevalence of MRSA in human contacts in relation to the last antibiotic intake clarified that the highest prevalence of MRSA in healthcare workers was recorded in the group informing that their last antibiotic intake was more than 1 year before sampling (40%) while the lowest prevalence was observed in the group informing that their last antibiotic intake was between 2 months and one year before sampling (23%).
• On the other side, the highest prevalence of MRSA in farm workers was recorded in the group informing that their last antibiotic intake was between 2 months and one year before sampling (58%) while the lowest prevalence was observed in the group informing that their last antibiotic intake was within 1 to 7 days before sampling (0.0%) highlighting the relationship between antibiotic administration and MRSA colonization.
• The antibiotic resistance of MRSA positive human isolates was carried out and it was observed that most isolates showed higher resistance for cefoxitin (92.5%) followed by tetracycline resistance (42.5%). In addition, linezolid resistance was observed in 25% of isolates that could be considered as increased percentage because linezolid resistance was very rare. Moreover, vancomycin resistance was observed in 12.5% of human isolates.
Concerning dairy cattle farms, 89 milk samples collected from dairy cattle farms were examined for detection of MRSA and 27 samples were identified as MRSA (30.33%). Also, swabs from 42 cups of milking machine were examined for MRSA and 38 were identified as MRSA contaminated (90.47%) that was considered very high percentage and could transmit MRSA to milk and handlers by contact. In addition, 135 cattle nasal swabs were tested and MRSA was identified in 65 (48.14%). These positive cows could be considered a potential source of MRSA to other cows and human. The relationship between occurrence of MRSA and mastitis in both milk samples and cattle was studied. It was found that MRSA was detected in milk samples collected from mastitic and healthy cows with the percentage of 70.37 and 29.63%, respectively. The antibiotic resistance of MRSA isolates obtained from cattle sources was studied and it was observed that most isolates showed higher resistance for cefoxitin (80.00%) in examined MRSA isolates followed by tetracycline (30.77%), vancomycin (16.92%) then linezolid (12.31%). Two samples were found to be resistant for the four antibiotics.
Finally, conventional polymerase chain reaction (PCR) was performed on 16 recovered isolates of MRSA for the presence of mecA gene and it was noticed that primer mecA was found in all the recovered isolates of MRSA. On contrary, a total of 10 isolates were screened for presence of PVL detection but they did not give the characteristic band for PVL and 4 isolates of MRSA were screened for presence of mecC gene but they did not give the characteristic band indicating the absence of target gene.