AN UNUSUAL OUTBREAK OF MASTITIS CAUSED BY METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS (MRSA) IN A DAIRY HERD IN THE NORTH OF ISRAEL, WINTER 2018

Staphylococcus aureus is one of the major pathogens in both humans and animals, leading to a wide variety of infections, including bovine-mastitis (~3% in Israel). In a survey conducted in the Laboratory for Udder Health (LUH), 1-12 Methicillin-resistant Staphylococcus aureus (MRSA)-infected cows were diagnosed annually (2012-2017) in Israel. However, during February 2018, an increased number of MRSA isolates originating from clinical and sub-clinical milk samples from a cooperative dairy farm in the north of Israel was noted. For a better understanding on the prevalence of this pathogen, milk samples were aseptically collected from all lactating cows (1,062), and admitted to LUH for bacteriologic culture and susceptibility tests. The results indicated that 11% of the cows (119) were infected with S. aureus and 95% of them were further diagnosed as MRSA. Susceptibility tests indicated that all MRSA isolates were resistant to penicillin, oxacillin, ubrolexin (cefalexin & kanamycin) and marbofloxacin; and susceptible to cefquinome, micospectone (spectinomycin & lincomycin) and rifaximine. Representative isolates were genotyped and assigned to spa type t011, MLST CC398 and confirmed to be positive for mecA. These characteristics are typical to "livestock-associated MRSA" (LA-MRSA), a major cause of disease in a variety of livestock animals and humans, especially in Europe. This is an unusual case of high prevalence of LA-MRSA mastitis in Israel.