Resistance to Antimicrobials and Biofilm Formation in Staphylococcus aureus Isolated from Bovine Mastitis in Beni-Suef Governorate

STAPHYLOCOCCUS (S.) aureus is one of the most prevalent causes of clinical and subclinical bovine mastitis. A total of 400 lactating cows housed in 5 farms in Beni-Suef governorate, Egypt, were examined for presenceof eitherclinical or subclinical mastitis. The examination revealed that 20 (5%) and 78 (21.8%) of animals showed clinical and subclinical mastitis criteria, respectively. Twenty three S. aureus isolates were recovered from 98 milk samples in a prevalence of 23.5%. Antimicrobial susceptibility testing of them against 8 compounds revealed that only one isolate was susceptible to all the tested antibiotics while high percentage (n=14, 60.9%) were resistant to more than one antibiotic. The highest percentage of resistance (82.6%) was documented against penicillin. Multiple drug resistance was observed in 26.1% of the tested isolates. Additionally 11(47.8%) isolates were resistant to cefoxitin so they were categorized phenotypically as methicillin-resistant S.aureus. All the recovered isolates were seeded on congo red agar to evaluate their biofilm forming ability and 18 (78.3%) of them were recorded as biofilm producers. Investigation of icaA, icaD and bap genes among the recovered isolates revealed that icaA and icaD were coexisted in 21 isolates (91.3%) while bap gene was existed in only one isolate (4.3 %).